U.S. patent application number 10/250171 was filed with the patent office on 2004-06-10 for voltage-controlled delay line with reduced timing errors and jitters.
Invention is credited to Chang, Hsiang-Hui, Liu, Shen-Iuan, Sun, Chih-Hao.
Application Number | 20040108872 10/250171 |
Document ID | / |
Family ID | 32466593 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040108872 |
Kind Code |
A1 |
Liu, Shen-Iuan ; et
al. |
June 10, 2004 |
VOLTAGE-CONTROLLED DELAY LINE WITH REDUCED TIMING ERRORS AND
JITTERS
Abstract
A voltage controlled delay line having a plurality of delay
cells is used to delay a first reference clock by a predetermined
delay time to generate an in-phase first delay clock and to delay a
second reference clock by the predetermined delay time to generate
an in-phase second delay clock. Each delay cell has a first input
port, a second input port, a first output port, and a second output
port. The first output port of one delay cell and the second input
port of another one delay cell having the same phase are
electrically connected or the second output port of one delay cell
and the first input port of another one delay cell having the same
phase are electrically connected so that the first and second input
port of each delay cell are not connected to the first and second
output port of an adjacent delay cell.
Inventors: |
Liu, Shen-Iuan; (Taipei
City, TW) ; Sun, Chih-Hao; (Taipei Hsien, TW)
; Chang, Hsiang-Hui; (Tao-Yuan Hsien, TW) |
Correspondence
Address: |
NAIPO (NORTH AMERICA INTERNATIONAL PATENT OFFICE)
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
32466593 |
Appl. No.: |
10/250171 |
Filed: |
June 10, 2003 |
Current U.S.
Class: |
326/93 |
Current CPC
Class: |
H03K 5/133 20130101;
H03K 5/1504 20130101; H03L 7/0891 20130101; H03L 7/0816 20130101;
H03K 2005/00032 20130101; H03K 2005/00208 20130101 |
Class at
Publication: |
326/093 |
International
Class: |
H03K 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2002 |
TW |
091135601 |
Claims
What is claimed is:
1. A clock adjustment circuit comprising: a clock generator for
generating a first reference clock signal and a second reference
clock signal; and a voltage controlled delay line for delaying the
first reference clock signal by a predetermined delay time to
generate a first delay clock signal and delaying the second
reference clock signal by the predetermined delay time to generate
a second delay clock signal, the first reference clock signal and
the first delay clock signal being in phase, the second reference
clock signal and the second delay clock signal being in phase, the
voltage controlled delay line comprising a plurality of delay cells
each delay cell comprising a first input port, a second input port,
a first output port, and a second output port, the delay cells
comprising: a first delay cell, a first input port of the first
delay cell electrically connected to the clock generator for
receiving the first reference clock signal; a second delay cell, a
first input port of the second delay cell electrically connected to
a first output port of the first delay cell through a first input
port and a first output port of at least a fifth delay cell, a
first output port of the second delay cell electrically connected
to a second input port of the first delay cell, a second input port
of the second delay cell electrically connected to a second output
port of the first delay cell through a first input port and a first
output port of at least a sixth delay cell and a second input port
and a second output port of at least a fifth delay cell; a third
delay cell, a first input port of the third delay cell electrically
connected to the clock generator for receiving the second reference
clock signal a second input port of the third delay cell
electrically connected to a second output port of the second delay
cell; and a fourth delay cell, a first input port of the fourth
delay cell electrically connected to a first output port of the
third delay cell through a second output port and a second input
port of at least a fifth delay cell and a first output port and a
first input port of at least a sixth delay cell, a second input
port of the fourth delay cell electrically connected to a second
output port of the third delay cell through a second input port and
a second output port of at least a sixth delay cell, a first output
port of the fourth delay cell used for outputting the first delay
clock signal, a second output port of the fourth delay cell used
for outputting the second delay clock signal; wherein a total
amount of the fifth delay cells is equal to a total amount of the
sixth delay cells.
2. The clock adjustment circuit of claim 1 wherein the first
reference clock signal and the second reference clock signal are
out of phase, and a period of the first reference clock signal is
equal to a period of the second reference clock signal.
3. The clock adjustment circuit of claim 2 wherein the
predetermined delay time is equal to the period of the first
reference clock signal.
4. The clock adjustment circuit of claim 1 being used in a delay
lock loop (DLL).
5. The clock adjustment circuit of claim 1 wherein loading
corresponding to a wire connected to a first output port of each
delay cell is equal to loading corresponding to a wire connected to
a second output port of each delay cell.
6. A clock adjustment circuit comprising: a clock generator for
generating a first reference clock signal and a second reference
clock signal; a voltage controlled delay line for delaying the
first reference clock signal by a predetermined delay time to
generate a first delay clock signal and delaying the second
reference clock signal by the predetermined delay time to generate
a second delay clock signal, the first reference clock signal and
the first delay clock signal being in phase, the second reference
clock signal and the second delay clock signal being in phase, the
voltage controlled delay line comprising a 2 n delay cells, each
delay cell comprising a first input port, a second input port, a
first output port, and a second output port, a first input port of
a m.sup.th delay cell within the 2 n delay cells either
electrically connected to the clock generator for receiving the
first reference clock signal or electrically connected to a first
output port of a (m-1).sup.th delay cell, a second input port of
the m.sup.th delay cell electrically connected to a first output
port of a (n+m-1).sup.th delay cell, a first output port of the
m.sup.th delay cell electrically connected to a first input port of
a (m+1).sup.th delay cell, a second output port of the m delay cell
either electrically connected to a second input port of the
(m+1).sup.th delay cell or electrically connected to a first input
port of a (n+m+1).sup.th delay cell, a first input port of a
(n+m).sup.th delay cell either electrically connected to a second
output port of the (m-1).sup.th delay cell or electrically
connected to the clock generator for receiving the second reference
clock signal, a second input port of the (n+m).sup.th delay cell
electrically connected to a second output port of the
(n+m-1).sup.th delay cell, a first output port of the (n+m).sup.th
delay cell electrically connected to a first input port of the
(n+m+1).sup.th delay cell, electrically connected to a second input
port of the (m+1).sup.th delay cell, or used for outputting the
first delay clock signal, a second output port of the (n+m).sup.th
delay cell electrically connected to a second input port of the
(n+m+1).sup.th delay cell or used for outputting the second delay
clock signal.
7. The clock adjustment circuit of claim 6 wherein the first
reference clock signal and the second reference clock signal are
out of phase, and a period of the first reference clock signal is
equal to a period of the second reference clock signal.
8. The clock adjustment circuit of claim 7 wherein the
predetermined delay time is equal to the period of the first
reference clock signal.
9. The clock adjustment circuit of claim 6 being used in a delay
lock loop (DLL).
10. The clock adjustment circuit of claim 6 wherein loading
corresponding to a wire connected to a first output port of each
delay cell is equal to loading corresponding to a wire connected to
a second output port of each delay cell.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a voltage-controlled delay
line. More specifically, the present invention discloses a
voltage-controlled delay line with an improved interconnection
among delay cells for reducing timing errors and jitters.
[0003] 2. Description of the Prior Art
[0004] Processing, exchanging, and distributing digital information
exists in a broad spectrum of fields. For example, digital devices
such as mobile phones, personal digital assistants (PDAs),
information applicants (IAS) that are connected to a computer
network, and personal computers are utilized to conveniently handle
digital information. When the digital device processes, exchanges,
and distributes digital information, the digital device requires
triggers generated from a clock signal to process digital data that
are sequentially transmitted. For instance, a central processing
unit (CPU) of a personal computer coordinates data transmitted
among digital circuits and data processed among the digital
circuits with the help of triggers generated from a clock signal.
In addition, with regard to a mobile phone, a clock signal is
necessary to let the mobile phone correctly transmit and receive
Wireless signals. Suppose that the mobile phone functions as a
receiver to receive incoming digital signals. In the beginning, the
mobile phone has to establish a local clock signal synchronized
with a timing associated with the incoming digital signals
outputted from a base station. Therefore, the mobile phone
successfully transmits wireless signals to the base station and
correctly receives-wireless signals outputted from the base station
according to the local clock signal synchronized with clock signal
used by the base station.
[0005] During a digital information processing procedure triggered
by clock signals, a well-known technique for generating a
synchronous clock signal based on a reference clock signal is
widely adopted. In digital circuits, a frequency associated with
one of two synchronous clock signals is multiplied or divided to
further obtain two synchronous clock signals with different
frequencies for conveniently handling digital data. In addition, it
is possible to generate a synchronous clock signal with a greater
driving capacity according to a reference clock signal. With regard
to a digital mobile communication system, when a mobile phone,
which functions as a receiver, needs to establish a local clock
signal according to timing of received signals, the received
signals have weak amplitudes so that the driving capacity of the
received signals is poor. Therefore, a synchronous clock having a
greater driving capacity and corresponding to timing of received
signals is necessary to drive the mobile phone to work
properly.
[0006] A circuit, which is capable of generating a synchronous
clock signal according to a reference clock signal, is called a
phase lock loop (PLL). One embodiment of the prior art PLL is a
so-called delay lock loop (DLL). Please refer to FIG. 1, which is
block diagram of a prior art DLL 10. The DLL 10 has a clock
generator 11, a voltage-controlled delay line 12, a phase detector
14, a charge pump 16, and two differential-to-single-ended
converters 18a, 18b. The clock generator 11 simultaneously outputs
a first reference clock signal CLK_REF+ and a second reference
clock signal CLK_REF-, where a phase difference between the first
reference clock signal CLK_REF+ and the second reference clock
signal CLK_REF- is equal to 180 degrees. That is, the first
reference clock signal CLK_REF+ and the second reference clock
signal CLK_REF- are out of phase. The voltage-controlled delay line
12, therefore, respectively delays the first reference clock signal
CLK_REF+ and the second reference clock signal CLK_REF- to generate
a first delay clock signal CLK_DL+ and a second delay clock signal
CLK_DL-. The differential-to-signal-ended converter 18a outputs a
first comparison signal CLK1 based on a magnitude difference
between the first reference clock signal CLK_REF+ and the second
reference clock signal CLK_REF-. A period of the first comparison
signal CLK1 is identical to a period of the first reference clock
signal CLK_REF+, and the period of the first comparison signal CLK1
is identical to a period of the second reference clock signal
CLK_REF- as well. Similarly, the differential-to-single-ende- d
converter 18b outputs a second comparison signal CLK2 based on a
magnitude difference between the first delay clock signal CLK_DL+
and the second delay clock signal CLK_DL-.
[0007] A period of the second comparison signal CLK2 is
theoretically identical to a period of the first delay clock signal
CLK_DL+, and the period of the second comparison signal CLK2 is
identical to a period of the second delay clock signal CLK_DL- as
well. Then, the phase detector 14 judges if the first delay clock
signal CLK_DL+ and the first reference clock signal CLK_REF+ are in
phase according to phases of the first comparison signal CLK1 and
the second comparison signal CLK2. In addition, the phase detector
14 also judges if the second delay clock signal CLK_DL- and the
second reference clock signal CLK_REF- are in phase according to
phases of the first comparison signal CLK1 and the second
comparison signal CLK2. When either rising edges or falling edges
of the first delay clock signal CLK_DL+ and the first reference
clock signal CLK_REF+ differ by an integral multiple of the period
of first reference clock signal CLK_REF+, the first delay clock
signal CLK_DL+ and the first reference clock signal CLK_REF+ are in
phase. Similarly, when either rising edges or falling edges of the
second delay clock signal CLK_DL- and the second reference clock
signal CLK_REF- differ by an integral multiple of the period of
second reference clock signal CLK_REF-, the second delay clock
signal CLK_DL- and the second reference clock signal CLK_REF- are
in phase.
[0008] After the phase detector 14 compares phases of the first
reference clock signal CLK1 and the second reference clock signal
CLK2, the phase detector 14 outputs control signals UP, DOWN to the
charge pump 16 according to the reference clock signal CLK1 leading
the second reference clock signal CLK2 or the reference clock
signal CLK1 lagging the second reference clock signal CLK2. After
the charge pump 16 receives the control signal DOWN, the charge
pump 16 raises voltage level of a control voltage Vpump. With
regard to voltage-controlled delay line 12, the increased control
voltage Vpump drives the voltage-controlled delay line 12 to delay
the first reference clock signal CLK_REF+ and the second reference
clock signal CLK_REF- through a longer delay time. On the other
hand, after the charge pump 16 receives the control signal UP, the
charge pump 16 lowers voltage level of the control voltage Vpump.
With regard to voltage-controlled delay line 12, the decreased
control voltage Vpump drives the voltage-controlled delay line 12
to delay the first reference clock signal CLK_REF+ and the second
reference clock signal CLK_REF- through a shorter delay time.
[0009] Please refer to FIG. 2 and FIG. 3. FIG. 2 is a first timing
diagram illustrating a phase lock process, and FIG. 3 is a second
timing diagram illustrating the phase lock process. Within FIG. 2
and FIG. 3, the waveforms from top to bottom respectively represent
the first comparison signal CLK1, the second comparison signal
CLK2, the control signal UP, the control signal DOWN, and time. For
example, the first reference clock signal CLK_REF+ and the second
reference clock signal CLK_REF-, which correspond to the first
comparison clock CLK1, are inputted into the voltage-controlled
delay line 12 at time t1. The voltage-controlled delay line 12
outputs the first delay clock signal CLK_DL+ and the second delay
clock CLK_DL-, which correspond to the second comparison signal
CLK2, after a delay time (t2-t1).
[0010] As shown in FIG. 2, the rising edge of the second comparison
clock CLK2 at time t2 leads the rising edge of the first comparison
signal CLK1 at time t3. That is, the phase of the second comparison
signal CLK2 leads the phase of the first comparison signal CLK1. In
other words, the delay time (t2-t1) introduced by the
voltage-controlled delay line 12 is less than the period (t3-t1)
corresponding to the first reference clock signal CLK_REF+ and the
second reference clock signal CLK_REF-. Therefore, the currently
adopted delay time should be increased. Therefore, the phase
detector 14 outputs the control signal DOWN at time t2 to the
charge pump 16 for raising the control voltage Vpump.
[0011] The first comparison signal CLK1 forms a rising edge at time
t3. At the same time, the control signal UP is issued by the phase
detector 14 during an interval . While the phase detector 14 resets
the control signal UP, the control signal DOWN is reset as well.
Therefore, the control signal UP and the control signal DOWN are
both reset at time t3+. As shown in FIG. 2, the delay time is now
adjusted to be (t4-t3). Because the rising edge of the second
comparison signal CLK2 at time t4 still leads the rising edge of
the first comparison signal CLK1 at time t5, the phase detector 14
outputs the control signal DOWN at time t4 to the charge pump
16.
[0012] When the first comparison signal CLK1 generates the rising
edge at time t5, the phase detector 14 outputs the control signal
UP during the interval . Then, the control signal UP and the
control signal DOWN are both reset at time t5+. The first
comparison signal CLK1 and the second comparison signal CLK2 are in
phase at time t6. That is, the first comparison signal CLK1 and the
second comparison signal CLK2 form rising edges simultaneously at
time t6. Therefore, the phase detector 14 outputs the control
signals UP, DOWN to the charge pump 16 during the same interval .
In other words, the control signals UP, DOWN are both reset at time
t6+.
[0013] Because the both control signals UP, DOWN have the same
power to affect the control voltage Vpump, the charge pump 16
therefore holds currently adopted control voltage Vpump without
being altered to drive the voltage-controlled delay line 12 for
locking the first and second reference clock signals CLK_REF+,
CLK_REF- and the in phase first and second delay clock signals
CLK_DL+, CLK_DL- corresponding to the first and second reference
clock signals CLK_REF+, CLK_REF-.
[0014] Please refer to FIG. 3, the first reference clock signal
CLK_REF+ and the second reference clock signal CLK_REF-, which
correspond to the first comparison clock CLK1, are inputted into
the voltage-controlled delay line 12 at time t1. The
voltage-controlled delay line 12 outputs the first delay clock
signal CLK_DL+ and the second delay clock CLK_DL-, which correspond
to the second comparison signal CLK2, after a delay time (t2-t1).
As shown in FIG. 3, the rising edge of the second comparison clock
CLK2 at time t3 lags the rising edge of the first comparison
signal. CLK1 at time t2. That is, phase of the second comparison
signal CLK2 lags phase of the first comparison signal CLK1. In
other words, the delay time (t3-t1) introduced by the
voltage-controlled delay line 12 is greater than the period (t2-t1)
corresponding to the first reference clock signal CLK_REF+ and the
second reference clock signal CLK_REF-. Therefore, the currently
adopted delay time should be cut down. Therefore, the phase
detector 14 outputs the control signal UP at time t2 to the charge
pump 16 for decreasing the control voltage Vpump.
[0015] The second comparison signal CLK1 forms a rising edge at
time t3. At the same time, the control signal DOWN is issued by the
phase detector 14 during an interval . While the phase detector 14
resets the control signal DOWN, the control signal UP is reset as
well. Therefore, the control signal UP and the control signal DOWN
are both simultaneously reset at time t3+. As shown in FIG. 3, the
delay time is now adjusted to be (t5-t2). Because the rising edge
of the second comparison signal CLK2 at time t5 still lags the
rising edge of the first comparison signal CLK1 at time t4, the
phase detector 14 outputs the control signal UP at time t4 to the
charge pump 16. When the second comparison signal CLK2 generates
the rising edge at time t5, the detector 14 outputs the control
signal DOWN during the interval . Then, the control signal UP and
the control signal DOWN are both reset at time t5+.
[0016] The first comparison signal CLK1 and the second comparison
signal CLK2 are in phase at time t6. That is, the first comparison
signal CLK1 and the second comparison signal CLK2 form rising edges
simultaneously at time t6. Therefore, the phase detector 14 outputs
the control signals UP, DOWN to the charge pump 16 during the same
interval. In other words, the control signals UP, DOWN are both
reset at time t6+.
[0017] Because the both control signals UP, DOWN have the same
power to affect the control voltage Vpump, the charge pump 16,
therefore, holds currently adopted control voltage Vpump without
being altered to drive the voltage-controlled delay line 12 for
locking the first and second reference clock signals CLK_REF+, CLK
REF- and the in phase first and second delay clock signals CLK_DL+,
CLK_DL- corresponding to the first and second reference clock
signals CLK_REF+, CLK_REF-.
[0018] Please refer to FIG. 4 and FIG. 5. FIG. 4 is a diagram of
the voltage-controlled delay line 12 shown in FIG. 1, and FIG. 5 is
a circuit diagram of a delay cell 20 shown in FIG. 4. The
voltage-controlled delay line 12 has a plurality of delay cells 20
that are cascaded in series. An output port out+ of a delay cell 20
is electrically connected to an input port in+ of a following delay
cell. Similarly, an output port out- of a delay cell 20 is
electrically connected to an input port in- of a following delay
cell. As shown in FIG. 5, the delay cell 20 corresponds to a
symmetrical circuit structure, and has a first circuit 22, a second
circuit 24, and a current source 26. A voltage Vb is used to
control current value provided by the current source 26, and the
control voltage Vpump outputted from the charge pump 16 is used to
control current values corresponding to the first circuit 22 and
the second circuit 24. However, with development of the
semiconductor process, the size of chips have become smaller.
Therefore, the circuits formed on the same chip are much closer
together than before. With regard to the deep sub-micro process,
one circuit component might easily affect another circuit
component.
[0019] For the first circuit 22 and the second circuit 24,
operational characteristics of both circuits are mismatched owing
to the advanced semiconductor process. That is, when the same
control voltage Vpump is inputted to the delay cell 20, the first
circuit 22 and the second circuit 24 generate different voltage
variations so that currents passing through the first circuit 22
and the second circuit 24 differ. Not only is the delay time
associated with the input port in+ and the output port out+
different from the delay time associated with the input port in-
and the output port out-, but the phase difference between the
input port in+ and the output port out+ and the phase difference
between the input port in- and the output port out- both deviate
from a predetermined value. For instance, if the voltage-controlled
delay line 12 has ten delay cells 20, and the input port and the
corresponding output port of each delay cell 20 corresponds to a
delay time Td. The voltage-controlled delay line 12 has a delay
cell 20 with mismatched first and second circuits 22, 24.
Therefore, with regard to the first circuit 22, the corresponding
delay time becomes Td+dT instead. On the other hand, the delay time
of the second circuit 24 then becomes Td-dT owing to the
above-mentioned symmetrical circuit structure.
[0020] It is shown in FIG. 4 that the voltage-controlled delay line
12 delays the first reference clock signal CLK_REF+ by a total
delay time 10*Td+dT for outputting the first delay clock signal
CLK_DL+. However, the voltage-controlled delay line 12 delays the
second reference clock signal CLK_REF- by a total delay time
10*Td-dT for outputting the second delay clock signal CLK_DL-. It
is obvious that each delay cell having mismatched first and second
circuits 22, 24 corresponds to a specific degree of influence upon
the associated delay time. In the end, problems with respect to
timing errors between the first and second reference clock signals
CLK_REF+, CLK_REF- and the first and second delay clock signals
CLK_DL+, CLK_DL- are introduced.
[0021] At the same time, the timing errors certainly cause the
periods corresponding to the delay clock signals CLK_DL+, CLK_DL-
to change continuously. Therefore, the jitters corresponding to the
delay clock signals CLK_DL+, CLK_DL- are great. If the component
size is increased to prevent the above-mentioned mismatch problem
when utilizing the deep sub-micro process to manufacture the DLL
10, the chip size increases and the related parasite capacitance
increases owing to an enlarged trace width. However, if an
additional calibration circuit is utilized to solve the
above-mentioned mismatch problem without increasing component size,
the hardware complexity will increase to raise an overall product
cost.
SUMMARY OF INVENTION
[0022] It is therefore a primary objective of this invention to
provide a voltage-controlled delay line capable of reducing timing
errors and jitters.
[0023] Briefly summarized, the preferred embodiment of the claimed
invention discloses a voltage-controlled delay line. The
voltage-controlled delay line includes a clock generator for
generating a first reference clock signal and a second reference
clock signal, and a voltage-controlled delay line for delaying the
first reference clock signal by a predetermined delay time to
generate a first delay clock signal and delaying the second
reference clock signal by the predetermined delay time to generate
a second delay clock signal. The first reference clock signal and
the first delay clock signal are in phase and the second reference
clock signal and the second delay clock signal are in phase.
[0024] The voltage-controlled delay line includes a plurality of
delay cells, and each delay cell has a first input port, a second
input port, a first output port, and a second output port. The
delay cells include a first delay cell, a second delay cell, a
third delay cell, and a fourth delay cell. A first input port of
the first delay cell is electrically connected to the clock
generator for receiving the first reference clock signal. A first
input port of the second delay cell is electrically connected to a
first output port of the first delay cell through a first input
port and a first output port of at least a fifth delay cell. A
first output port of the second delay cell is electrically
connected to a second input port of the first delay cell. A second
input port of the second delay cell is electrically connected to a
second output port of the first delay cell through a first input
port and a first output port of at least a sixth delay cell and a
second input port and a second output port of at least a fifth
delay cell. A first input port of the third delay cell is
electrically connected to the clock generator for receiving the
second reference clock signal a second input port of the third
delay cell electrically connected to a second output port of the
second delay cell. A first input port of the fourth delay cell is
electrically connected to a first output port of the third delay
cell through a second output port and a second input port of at
least a fifth delay cell and a first output port and a first input
port of at least a sixth delay cell. A second input port of the
fourth delay cell is electrically connected to a second output port
of the third delay cell through a second input port and a second
output port of at least a sixth delay cell. A first output port of
the fourth delay cell is used for outputting the first delay clock
signal. A second output port of the fourth delay cell is used for
outputting the second delay clock signal. In addition, a total
amount of the fifth delay cells is equal to a total amount of the
sixth delay cells.
[0025] It is an advantage of the claimed invention that the claimed
voltage-controlled delay line either connects a first output port
of one delay cell and a second input port of another delay cell
where the first output port of one delay cell and the second input
port of another delay cell correspond to the same phase, or
connects a first input port of one delay cell and a second output
port of another delay cell where the first output port of one delay
cell and the second input port of another delay cell correspond to
the same phase. In other words, the first and second input ports of
a delay cell are not simultaneously connected to the corresponding
first and second output ports of an adjacent delay cell. Therefore,
the timing errors associated with adjacent delay cells are
independent so that the timing errors and the corresponding jitters
are reduced.
[0026] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment, which is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is block diagram of a prior art delay lock loop.
[0028] FIG. 2 is a first timing diagram illustrating a phase lock
process.
[0029] FIG. 3 is a second timing diagram illustrating the phase
lock process.
[0030] FIG. 4 is a diagram of a voltage-controlled delay line shown
in FIG. 1.
[0031] FIG. 5 is a circuit diagram of a delay cell shown in FIG.
4.
[0032] FIG. 6 is a diagram of a voltage-controlled delay line
according to the present invention.
[0033] FIG. 7 is a phase diagram of output signals generated from
delay cells shown in FIG. 6.
DETAILED DESCRIPTION
[0034] Please refer to FIG. 6 and FIG. 7. FIG. 6 is a diagram of a
voltage-controlled delay line 30 according to the present
invention, and FIG. 7 is a phase diagram of output signals
generated from delay cells 20 shown in FIG. 6. The
voltage-controlled delay line 30 includes a plurality of delay
cells 20. Please note that the delay cell 20 on the preferred
embodiment has a circuit structure identical to the circuit
structure shown in FIG. 5. In addition, in order to describe
conveniently features of the present invention, the
voltage-controlled delay line 30 in the preferred embodiment only
has delay cells whose amount corresponds to an even number such as
ten. That is, ten delay cells DL1.about.DL10 within the
voltage-controlled delay line 30 are used to illustrate
functionality of the voltage-controlled delay line 30.
[0035] As mentioned above, the voltage-controlled delay line 30 is
primarily used to delay the first reference clock signal CLK_REF+
to output the first delay clock signal CLK_DL+ where the first
reference clock signal CLK_REF+ and the first delay clock signal
CLK_DL+ are in phase. In other words, the rising edge of the first
delay clock signal CLK_DL+ is synchronized with the rising edge of
the first reference clock signal CLK_REF+. Therefore, an interval
between the rising edge of the first delay clock signal CLK_DL+ and
the rising edge of the first reference clock signal CLK_REF+ is
equal to an integralmultiple of the period of the first reference
clock signal CLK_REF+. The first reference clock signal CLK_REF+
and the second reference clock signal CLK_REF- are out of phase so
that phase of the first reference clock signal CLK_REF+ and phase
of the second reference clock signal CLK_REF- differs by 180
degrees.
[0036] Similarly, the voltage-controlled delay line 30 also delays
the second reference clock signal CLK_REF- to output the second
delay clock signal CLK_DL- where the second reference clock signal
CLK_REF- and the second delay clock signal CLK_DL- are in phase. In
other words, the rising edge of the second delay clock signal
CLK_DL- is synchronized with the rising edge of the second
reference clock signal CLK_REF-. Therefore, an interval between the
rising edge of the second delay clock signal CLK_DL- and the rising
edge of the second reference clock signal CLK_REF- is equal to an
integralmultiple of the period of the second reference clock signal
CLK_REF-. It is noteworthy that period of the first reference clock
signal CLK_REF+ is equal to period of the second reference clock
signal CLK_REF-.
[0037] The following description associated with the preferred
embodiment describes the voltage-controlled delay line 30 locking
one period T of the first reference clock signal CLK_REF+.
Therefore, each of the delay cells DL1.about.DL10 corresponds to a
delay time (1/10)*T. From the viewpoint of the phase relationship,
each delay cell DL1.about.DL10 makes an output signal and an input
signal correspond to a phase difference (360.degree./10). It is
known that the first reference clock signal CLK_REF+ and the first
delay clock signal CLK_DL+ are in phase. As shown in FIG. 7, when
the first reference clock signal CLK_REF+ corresponds to phase
0.degree., the first delay clock signal CLK_DL+ corresponds to
phase 0.degree.as well. Each of the delay cells DL1.about.DL10
corresponds to the phase difference (360.degree./10) when
processing the first reference clock signal CLK_REF+. Therefore,
output signals CLK1+.about.CLK9+ outputted from delay cells
DL1.about.DL9 counterclockwise divide the 360 degrees associated
with one period T, and the distribution result of the output
signals CLK1+.about.CLK9+ is shown in FIG. 7.
[0038] The-first reference clock signal CLK_REF+ and the second
reference clock signal CLK_REF- are out of phase so that the phase
difference between the first reference clock signal CLK_REF+ and
the second reference clock signal CLK_REF- is equal to 180 degrees.
Therefore, when the first reference clock signal CLK_REF+
corresponds to 0.degree., the second reference clock signal
CLK_REF- then corresponds to 180.degree.. Similarly, the output
signals CLK1,-.about.CLK9- outputted from delay cells DL1.about.DL9
counterclockwise divide the 360 degrees associated with one period
T, and the distribution result of the output signals
CLK1-.about.CLK9- is shown in FIG. 7. It is obvious that one phase
corresponds to different output signals. For instance, the output
signal CLK1- generated from the delay cell DL1 and the output
signal CLK6+ generated from the delay cell DL6 are in phase. In
other words, the output signal CLK1- and output signal CLK6+ are
capable of substituting for each other without affecting
functionality of the voltage-controlled delay line 30.
[0039] In the preferred embodiment, the output signal CLK1- is used
to the output signal CLK6+ outputted from the delay cell DL6 for
driving the next delay cell DL7, and the output signal CLK6+ is
then used to replace the output signal CLK1- generated from the
delay cell DL1 for driving the next delay cell DL2. Similarly, each
group of the output signals CLK2-, CLK7+, the output signals CLK3-,
CLK8+, and the output signals CLK4-, CLK9+ corresponds to the same
substitution rule mentioned above to establish the interconnection
within the voltage-controlled delay line 30 shown in FIG. 6.
[0040] It is noteworthy that the total amount of delay cells 20
needs to equal an even number in order to make output signals
correspond to the phase relation shown in FIG. 7. In other words,
any phase shown in FIG. 7 is capable of corresponding to a
plurality of output signals. In addition, the voltage-controlled
delay line 30 shown in FIG. 6 is a preferred embodiment where the
above-mentioned substitution rule is applied to each group of the
output signals CLK1-, CLK6+, output signals CLK2-, CLK7+, output
signals CLK3-, CLK8+, and output signals CLK4-, CLK9+. However,
based on the phase relation shown in FIG. 7, different output
signals corresponding to the same phase (the output signals CLK2-,
CLK7+ for example) can substitute for each other to adjust
interconnection between delay cells 20 within the prior art
voltage-controlled delay line 12 shown in FIG. 4.
[0041] Operation of the voltage-controlled delay line 30 is
described as follows. As shown in FIG. 4, it is obvious that the
first circuit 22 and the second circuit 24 are symmetrical and are
electrically connected to the same current source 26. For example,
if one delay time is equal to Td+, another delay time is certainly
equal to Td- owing to the symmetrical circuit structure. On the
other hand, if one delay time is equal to Td-, another delay time
is certainly equal to Td+ owing to the symmetrical circuit
structure. That is, when output port out+ and input port in+ in
each of the delay cells DL1.about.DL10 correspond to a delay time
Td.+-., output port out- and input port in- in each of the delay
cells DL1.about.DL10 will correspond to a delay time Td
[0042]
[0043] Suppose that an ideal delay time for each of the delay cells
DL1.about.DL10 is equal to Td. However, if at least one delay cell
(delay cell DL1 for example) has the above-mentioned mismatch
problem, the corresponding delay times become Td.+-.1 and Td
[0044] 1 that deviate from the ideal delay time Td. Please note
that only the delay cell DL1 with the deviation .+-.1 is used to
illustrate operation of the claimed voltage-controlled delay line
30 for simplicity. However, each of the delay cells DL1.about.DL10
actually has a corresponding deviation owing to its own mismatched
circuit structure.
[0045] After the first reference clock signal CLK_REF+ is inputted
into the delay cell DL1, the delay cell DL1 imposes the delay time
Td.+-.1 on the first reference clock signal CLK_REF+ to generate
the output signal CLK1 + that is then transmitted to the next delay
cell DL2. With the contribution of the delay cell DL2, the total
delay time for the first reference clock signal CLK_REF+ becomes 2
Td.+-.1. Similarly, with the help of the following delay cells DL3,
DL4, DL5, the total delay time for the first reference clock signal
CLK_REF+ becomes 5 Td.+-.1. Please note that output signal CLK5+ of
the delay cell DL5 is substituted for the second reference clock
signal CLK_REF-, and the output signal CLK5+ is then inputted into
the delay cell DL1. Therefore, the total delay time imposed on the
first reference clock signal CLK_REF+ becomes 6 Td, that is, 5
Td.+-.1+Td 1. At the same time, output signal CLK1- of the delay
cell DL1 substitutes the output signal CLK6+ of the delay cell DL6,
and is transmitted to the delay cell DL7. Therefore, with
contribution of the delay cell DL7, the total delay time becomes 7
Td. Based on the circuit structure shown in FIG. 6, the delay cells
DL1, DL2, DL3, DL4, DL5, DL1, DL7, DL3, DL9, DL5, DL6 DL7, DL8,
DL9, DL10 are sequentially activated to delay the first reference
clock signal CLK_REF+ for generating the second delay clock signal
CLK_DL-.
[0046] It is obvious that the total delay time imposed on the first
reference clock signal CLK_REF+ is equal to 15 Td. Therefore, the
simultaneously introduced deviations +1 and -1 owing to the
mismatched circuit structure inside the delay cell DL1 are
automatically cancelled during the whole delay process for
generating the second delay clock signal CLK_DL-. In addition,
after the second reference clock signal CLK_REF- is inputted into
the delay cell DL6, the delay cells DL6, DL2, DL8, DL4, DL10 are
sequentially activated to delay the second reference clock signal
CLK_REF- for generating the first delay clock signal CLK_DL+
according to the circuit structure shown in FIG. 6. Therefore, when
the first delay clock signal CLK_DL+ is outputted, the total delay
time corresponding to the first delay clock signal CLK_DL+ is equal
to 5 Td.
[0047] With regard to timing errors caused by the symmetrical
circuit structure within each of the delay cells DL1.about.DL10 of
the voltage-controlled delay line 30, each of the delay cells
DL1.about.DL10 in the preferred embodiment is not sequentially
activated to delay received signals. The preferred embodiment
alters interconnection among the delay cells DL1.about.DL10 in the
prior art voltage-controlled delay line 12 to adjust the prior art
execution sequence associated with the delay cells DL1.about.DL10
in the prior art voltage-controlled delay line 12. According to the
phase relation shown in FIG. 7, the output signals corresponding to
the same phase can substitute each other to further average timing
errors such as +1 and -1 so the timing errors affecting the
voltage-controlled delay line 30 are greatly reduced.
[0048] Within the prior art voltage-controlled delay line 12 shown
in FIG. 4, the delay cells DL1.about.DL10 are cascaded in series.
In other words, one delay cell generates a timing error, and
directly introduces the timing error to the next delay cell for
superposing the timing error on the timing error of the next delay
cell. Therefore, the timing errors associated with adjacent delay
cells are dependent. However, within the claimed voltage-controlled
delay line 30, two input ports in+, in- of one delay cell are
electrically connected to output ports out+, out- respectively
belonging to different delay cells. Taking the delay cell DL2 shown
in FIG. 6 for example, one input port is electrically connected to
one output port of the delay cell DL1, but another input port of
the delay cell DL2 is electrically connected to output port of the
delay cell DL6. In other words, the timing errors of adjacent delay
cells are independent.
[0049] According to H. Gian, R. Raf, "A 65-mW, 10-bit, 40-M samples
BiCMOS Nyquist ADC in 0.8 mm.sup.2", IEEE J.Solid-State Circuits,
Vol. 34, no. 12, pp. 1796.about.1802, December 1999, it is
well-known that if a random timing error associated with the delay
cell in the prior art voltage-controlled delay line 12 is equal to
.quadrature., a random timing error associated with the delay cell
in the claimed voltage-controlled delay line 30 then becomes
[0050] Because the timing errors make the periods of the first and
second delay clock signals CLK_DL+, CLK_DL- alter continuously,
jitters associated to the first and second delay clock signals
CLK_DL+, CLK_DL- are generated. Therefore, when the random timing
error is reduced to be the original random timing error, a jitter
corresponding to the claimed voltage-controlled delay line 30 is
certainly reduced to be of the original jitter corresponding to the
prior art voltage-controlled delay line 12.
[0051] In addition, an experimental result of a peak-to-peak jitter
corresponding to a worst case associated with adjacent periods
shows that the claimed voltage-controlled delay line 30 is capable
of greatly reducing jitters. It is noteworthy that the traces
connecting the delay cells introduce parasite capacitance to the
voltage-controlled delay line 30. Therefore, the circuit layout for
the claimed voltage-controlled delay line 30 is designed to make
both output ports of one delay cell correspond to the same loading
to prevent the traces from being mismatched to affect operation of
the claimed voltage-controlled delay line 30.
[0052] In contrast to the prior art voltage-controlled delay line,
the claimed voltage-controlled delay line either connects a first
output port of one delay cell and a second input port of another
delay cell where the first output port of one delay cell and the
second input port of another delay cell correspond to the same
phase, or connects a first input port of one delay cell and a
second output port of another delay cell where the first output
port of one delay cell and the second input port of another delay
cell correspond to the same phase. In other words, the first and
second input ports of a delay cell are not simultaneously connected
to the corresponding first and second output ports of an adjacent
delay cell. The claimed voltage-controlled delay line only alters
interconnection among delay cells of the prior art
voltage-controlled delay line. Therefore, no additional circuit
component is needed. It is easy to implement the desired
interconnection within the claimed voltage-controlled delay line,
and the timing errors and jitters are greatly reduced to improve
performance of the prior art voltage-controlled delay line.
[0053] Those skilled in the art will readily observe that numerous
modifications and alterations of the device may be made while
retaining the teachings of the invention. Accordingly, the above
disclosure should be construed as limited only by the metes and
bounds of the appended claims.
* * * * *