U.S. patent application number 12/071485 was filed with the patent office on 2009-08-27 for preamplifier for receiver and method thereof.
This patent application is currently assigned to HIMAX TECHNOLOGIES LIMITED. Invention is credited to Chih-Haur Huang, Chung-Ming Huang.
Application Number | 20090212864 12/071485 |
Document ID | / |
Family ID | 40942663 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090212864 |
Kind Code |
A1 |
Huang; Chih-Haur ; et
al. |
August 27, 2009 |
PREAMPLIFIER FOR RECEIVER AND METHOD THEREOF
Abstract
A preamplifier used in a receiver is provided. The preamplifier
comprises an input circuit and an output circuit. The input circuit
receives an input differential voltage pair, pulls it down when the
common voltage of the input differential voltage pair is higher
than a reference voltage. The output circuit receives the input
differential voltage pair outputted from the input circuit to pull
high or low an output voltage accordingly.
Inventors: |
Huang; Chih-Haur; (Tainan
County, TW) ; Huang; Chung-Ming; (Tainan County,
TW) |
Correspondence
Address: |
RABIN & Berdo, PC
1101 14TH STREET, NW, SUITE 500
WASHINGTON
DC
20005
US
|
Assignee: |
HIMAX TECHNOLOGIES LIMITED
Tainan County
TW
|
Family ID: |
40942663 |
Appl. No.: |
12/071485 |
Filed: |
February 21, 2008 |
Current U.S.
Class: |
330/258 |
Current CPC
Class: |
H03F 2203/45616
20130101; H03F 3/3022 20130101; H03F 3/4521 20130101; H03F 3/45704
20130101; H03F 2203/45008 20130101; H03F 2203/45586 20130101; H03F
2203/45074 20130101; H03F 2203/45078 20130101 |
Class at
Publication: |
330/258 |
International
Class: |
H03F 3/45 20060101
H03F003/45 |
Claims
1. A preamplifier used in a receiver, comprising: an input circuit
receiving an input differential voltage pair, pulling it down when
the common voltage of the input differential voltage pair is higher
than a reference voltage; and an output circuit receiving the input
differential voltage pair outputted from the input circuit to pull
high or low an output voltage accordingly.
2. The preamplifier according to claim 1, wherein the input circuit
keeps the input differential voltage pair unchanged when the common
voltage of the input differential voltage pair is not higher than
the reference voltage.
3. The preamplifier according to claim 1, wherein the input circuit
comprises: a comparator comparing the common voltage of the input
differential voltage pair with the reference voltage; and a level
adjustment circuit pulling down the input differential voltage pair
when the common voltage of the input differential voltage pair is
higher than the reference voltage.
4. The preamplifier according to claim 3, wherein the level
adjustment circuit comprises two source followers, each of which
pulling down one voltage of the input differential voltage pair
when the common voltage is higher than the reference voltage.
5. The preamplifier according to claim 3, wherein the input circuit
comprising a voltage divider generating the common voltage of the
input differential voltage pair to the comparator.
6. The preamplifier according to claim 3, wherein the input circuit
comprises a first switch, a second switch, a third switch and a
fourth switch, the first and the second switches transfer the input
differential voltage pair to the level adjustment circuit when the
common voltage is higher than the reference voltage, the third and
the fourth switches transfer the differential voltage pair directly
to the output circuit when the common voltage is not higher than
the reference voltage.
7. The preamplifier according to claim 1, wherein the output
circuit comprises: a first stage amplifier, powered by a high
supply voltage, receiving the input differential voltage pair
outputted from the input circuit and amplifying the input
differential voltage pair to output an internal differential
voltage pair; and a second stage amplifier, powered by a low supply
voltage and amplifying the internal differential voltage pair to
pull high or low a first output voltage.
8. The preamplifier according to claim 1, wherein the output
circuit further comprises: an inverter pulling high or low a second
output voltage based on the first output voltage.
9. A preamplifier used in a receiver, comprising: an input circuit
receiving an input differential voltage pair, pulling it down when
the common voltage of the input differential voltage pair is higher
than a reference voltage, and keeping it unchanged when the common
voltage is not higher than the reference voltage; and an amplifier
comprising: a first stage amplifier, powered by a high supply
voltage, for receiving and amplifying the input differential
voltage pair outputted from the input circuit to output an internal
differential voltage pair; and a second stage amplifier, powered by
a low supply voltage, for receiving and amplifying the internal
differential voltage pair to pull high or low an output
voltage.
10. The preamplifier according to claim 9, wherein the input
circuit comprises: a comparator comparing the common voltage of the
input differential voltage pair with the reference voltage; and a
level adjustment circuit pulling down the input differential
voltage pair when the common voltage of the input differential
voltage pair is higher than the reference voltage.
11. The preamplifier according to claim 10, wherein the level
adjustment circuit comprises two source followers, each of which
pulling down one voltage of the input differential voltage pair
when the common voltage is higher than the reference voltage.
12. The preamplifier according to claim 10, wherein the input
circuit comprising a voltage divider generating the common voltage
of the input differential voltage pair to the comparator.
13. The preamplifier according to claim 10, wherein the input
circuit comprises a first switch, a second switch, a third switch
and a fourth switch, the first and the second switches transfer the
input differential voltage pair to the level adjustment circuit
when the common voltage is higher than the reference voltage, the
third and the fourth switches transfer the differential voltage
pair directly to the output circuit when the common voltage is not
higher than the reference voltage.
14. The preamplifier according to claim 9, wherein the output
circuit further comprises: an inverter pulling high or low a second
output voltage based on the first output voltage.
15. A method for preamplifying an input differential voltage pair,
used in a receiver, comprising: pulling down the input differential
voltage pair when the common voltage of the input differential
voltage pair is higher than a reference voltage; amplifying the
input differential voltage pair to output an internal differential
voltage pair; and amplifying the internal differential voltage pair
to pull high or low a first output voltage.
16. The method according to claim 15, wherein before the step of
amplifying the input differential voltage pair, the method further
comprises: when the common voltage of the input differential
voltage pair is not higher than the reference voltage, keep the
input differential voltage pair unchanged.
17. The method according to claim 15, wherein in the step of
amplifying the input differential voltage pair, amplify the input
differential voltage pair to output an internal differential
voltage pair by a first stage amplifier powered by a high supply
voltage.
18. The method according to claim 15, wherein in the step of
amplifying the internal differential voltage pair, amplify the
internal differential voltage pair by a second stage amplifier
powered by a low supply voltage.
19. The method according to claim 15, wherein the method further
comprises: amplifying the first output voltage to pull high or low
a second output voltage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates in general to a preamplifier for a
receiver and a method thereof, and more particularly to a
preamplifier with wide range of the common voltage of the input
differential voltage pair.
[0003] 2. Description of the Related Art
[0004] FIG. 1 is a circuit diagram of a conventional rail-to-rail
preamplifier for a receiver. The conventional rail-to-rail
preamplifier 100 includes amplifiers 110 and 120 and an inverter
130. The amplifiers 110 and 120 each amplify a differential voltage
pair VN and VP and produce one voltage of the amplified
differential voltage pair for the inverter 130. The inverter 130
then pulls its output voltage Vo high or low based on these inputs.
The transistors in amplifiers 110 and 120 are complementary, so
that the preamplifier 100 is capable of amplifying the differential
voltage VN and VP with wide common voltage range.
[0005] However, the amplifiers 110 and 120 are powered by a high
voltage supply power HVDD, which is for analog power, while the
inverter 130 is powered by a low voltage supply power LVDD, which
is for digital power. The high supply voltage HVDD is around 3.3V,
and the low supply voltage LVDD is around 1.8V. The low supply
voltage LVDD is even lower than the high supply voltage HVDD minus
a threshold voltage of a transistor 121 in amplifier 120. Thus, the
transistor 131 in the inverter 130 is cut off, which causes the
rail-to-rail preamplifier to become disabled.
SUMMARY OF THE INVENTION
[0006] A preamplifier used in a receiver includes an input circuit,
an output circuit. The input circuit receives an input differential
voltage pair and pulls it down when the common voltage of the input
differential voltage pair is higher than a reference voltage. The
output circuit receives the input differential voltage pair
outputted from the input circuit to pull high or low an output
voltage accordingly.
[0007] A preamplifier used in a receiver includes an input circuit
and an amplifier. The input circuit receives an input differential
voltage pair, pulls it down when the common voltage of the input
differential voltage pair is higher than a reference voltage, and
keeps it unchanged when the common voltage is not higher than the
reference voltage. The amplifier includes a first stage amplifier
and a second stage amplifier. The first stage amplifier, powered by
a high supply voltage, receives and amplifies the input
differential voltage pair outputted from the input circuit to
output an internal differential voltage pair. The second stage
amplifier, powered by a low supply voltage, receives and amplifies
the internal differential voltage pair to pull high or low an
output voltage.
[0008] A method for preamplifying an input differential voltage
pair, used in a receiver, includes the following steps. Firstly,
the input differential voltage pair is pulled down when the common
voltage of the input differential voltage pair is higher than a
reference voltage. Next, the input differential voltage pair is
amplified to output an internal differential voltage pair. Then,
the internal differential voltage pair is amplified to pull high or
low a first output voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a circuit diagram of a conventional rail-to-rail
preamplifier for a receiver.
[0010] FIG. 2 shows a circuit diagram of the preamplifier according
to a first embodiment of the invention.
[0011] FIG. 3 shows a circuit diagram of the preamplifier according
to a second embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0012] FIG. 2 shows a circuit diagram of the preamplifier 200
according to the first embodiment of the invention. The
preamplifier 200 is for preamplifying an input differential voltage
pair VIN and VIP to pull an output voltage Vo1 for a receiver high
or low.
[0013] preamplifier 200 includes an input circuit 210 and an output
circuit 220. The input circuit 210 receives the input differential
voltage pair VIN and VIP. In the first embodiment, when the common
voltage Vcom of the input differential voltage pair VIN and VIP is
higher than a reference voltage Vr, the input circuit 210 pulls the
input differential voltage pair VIN and VIP down to produce a
differential voltage pair VIN' and VIP' and then transfers the
differential voltage pair VIN' and VIP' to the output circuit
220.
[0014] When the common voltage Vcom of the input differential
voltage pair VIN and VIP is not higher than the reference voltage
Vr, the input circuit 210 directly transfers the input differential
voltage pair VIN and VIP as the input differential voltage pair
VIN' and VIP' to the output circuit 220 without pulling the input
differential voltage pair VIN and VIP down. The output circuit 220
then takes the input differential voltage pair VIN' and VIP' and
pulls the output voltage Vo1 high or low.
[0015] The input circuit 210 is now described in detail. The input
circuit 210 includes a comparator 230 and a level adjustment
circuit 240 and switches 261, 262, 263 and 264. The comparator 230
compares the common voltage Vcom of the input differential voltage
pair VIN and VIP with the reference voltage Vr. The switches 261 to
264 are turned on or off based on the comparing result of the
comparator 230.
[0016] When the common voltage Vcom is higher than the reference
voltage Vr, the switches 263 and 264 are turned on to transmit the
input differential voltage pair VIN and VIP to the level adjustment
circuit 240. Meanwhile, the switches 261 and 262 are turned off
with the result that the input differential voltage pair will not
be directly transmitted to the output circuit 220. The level
adjustment circuit 240 then pulls the input differential voltage
pair VIN and VIP down. The pulled-down input differential voltage
pair VIN and VIP is then transferred to the first stage amplifier
270 in the output circuit 220.
[0017] In this embodiment, the level adjustment circuit 240
includes source followers 241 and 242, which are for pulling down
the voltages VIN and VIP, respectively, of the input differential
voltage pair when the common voltage Vcom is higher than the
reference voltage Vr. The source follower 241 includes transistors
243 and 244. When the common voltage Vcom is higher than the
reference voltage Vr, the gate of the transistor 243 receives the
voltage VIP. The drain of the transistor 243 receives the high
supply voltage HVDD and its source is connected to the drain of the
transistor 244. The transistor 244 has its source grounded.
[0018] When the transistor 243 receives the voltage VIP, the
transistor 243 pulls down the voltage VIP by an amount equal to its
gate-source cross voltage to produce the voltage VIP' at its source
which is connected to the output circuit 220.
[0019] Similarly, when the common voltage Vcom is higher than the
reference voltage Vr, the gate of the transistor 245 receives the
voltage VIN. Then the transistor 245 pulls down the voltage VIN by
an amount equal to its gate-source cross voltage to produce the
voltage VIN' at its source which is connected to the output circuit
220.
[0020] When the common voltage Vcom is not higher than the
reference voltage Vr, the switches 261 and 262 are turned on to
transfer the voltages VIN and VIP to the output circuit 220 as the
voltages VIN' and VIP', respectively,. Meanwhile, the switches 263
and 264 are turned off with the result that the level adjustment
circuit 240 will not receive the input differential voltage pair
VIN and VIP. Therefore, when the common voltage Vcom is not higher
than the reference voltage Vr, the input differential voltage pair
VIN and VIP is not pulled down but directly transferred to the
output circuit 220.
[0021] In this embodiment, the input circuit 210 further includes a
voltage divider 250 to generate the common voltage Vcom of the
input differential voltage pair VIN and VIP to the comparator 230.
In the first embodiment, the voltage divider 250 is a resistor
string including resistors 251 and 252 which are serially
connected. The voltage divider 250 is coupled between the voltage
VIN and the voltage VIP to divide the voltage therebetween. In the
first embodiment, the resistances of the resistors 251 and 252 are
the same. Thus, the common voltage Vcom of the input differential
voltage pair VIN and VIP is produced at the connection of the
resistors 251 and 252.
[0022] The output circuit 220 is now described in detail. In the
first embodiment, the output circuit 220 is an amplifier. The
output circuit 220 includes a first stage amplifier 270 and a
second stage amplifier 280. In the first embodiment, the first
stage amplifier 270 is powered by the high supply voltage HVDD,
which is for analog power, while the second stage amplifier 280 is
powered by the low supply voltage LVDD, which is for digital power.
The first stage amplifier 270 receives and amplifies the input
differential voltage pair VIN' and VIP' produced by the input
circuit 210 and produces an internal differential voltage pair Vin
and Vip. The second stage amplifier 280 receives and amplifies the
internal differential voltage pair Vin and Vip to pull the output
voltage Vo1 high or low.
[0023] The first stage amplifier 270 includes transistors 271, 272,
273. The transistor 271 is for receiving the high supply voltage
HVDD and providing a bias current for the first stage amplifier
270. The transistors 272 and 273 are for receiving the voltages
VIN' and VIP', respectively. The source-drain cross voltage of the
transistor 271 is Vsd. The source-gate cross voltage of the
transistors 272 and 273 are Vsg.
[0024] The second stage amplifier 280 includes transistors 281,
282, 283, and 284. The transistors 281 and 282 form a current
mirror. The transistors 283 and 284 receive the voltage Vip and
Vin, respectively.
[0025] In the first embodiment, the output circuit 220 further
includes an inverter 290 for amplifying the output voltage Vo1 to
produce an inverted output voltage Vo2.
[0026] When the voltage VIP is higher than the voltage VIN, that
is, the voltage VIP' is higher than the voltage VIN', the amplifier
280 pulls the output voltage Vo1 low, and the inverter 290 then
pulls the output voltage Vo2 high. When the voltage VIP is lower
than the voltage VIN, that is, the voltage VIP' is lower than the
voltage VIN', the amplifier 280 pulls the output voltage Vo1 high
and the inverter 290 then pulls the output voltage Vo2 low.
[0027] Therefore, the preamplifier 200 receives the input
differential voltage pair VIN and VIP and pulls the output voltages
Vo1 and Vo2 high or low according to the input differential
voltage.
[0028] However, when the common voltage of the input differential
voltage pair VIN' and VIP' is higher than the voltage HVDD-Vsd-Vsg,
the transistors 272 and 273 will be cut off, which causes the
output circuit 220 to be disabled. Therefore, by applying the input
circuit 210, which pulls down the input differential voltage pair
VIN and VIP when the common voltage Vcom of the input differential
voltage pair VIN and VIP is too high, the transistors 272 and 273
are therefore enabled to receive the pulled-down input differential
voltage VIN' and VIP' so as to be kept turned on.
[0029] In the first embodiment, the reference voltage Vr is set to
about HVDD/2, which ensures that the pulled down input differential
voltage pair VIN' and VIP' are not to cut off to the transistors
272 and 273.
[0030] Conversely, when the common voltage Vcom of the input
differential voltage pair VIN and VIP is not higher than the
reference voltage Vr, the input circuit 210 simply reproduces VIN
and VIP as the differential voltage pair VIN' and VIP' at its
output, in which case the transistors 272 and 273 will not be cut
off.
[0031] Therefore, even if the common voltage Vcom of the input
differential voltage pair VIN and VIP is high, the common voltage
of the input differential voltage pair VIN' and VIP' produced by
the input circuit 210 will not be higher than the voltage
HVDD-Vsd-Vsg, so that the output circuit 220 works properly. Thus,
the preamplifier 200 according to the first embodiment is capable
of properly preamplifying the input differential voltage pair even
with wide range of common voltage.
Second Embodiment
[0032] FIG. 3 shows a circuit diagram of the preamplifier 300
according to the second embodiment. In the second embodiment, when
the common voltage Vcom' of the input differential voltage pair DIN
and DIP is lower than a reference voltage Vr', the input circuit
310 pulls the input differential voltage pair DIN and DIP up to
produce a differential voltage pair DIN' and DIP' and then
transfers the differential voltage pair DIN' and DIP' to the output
circuit 320.
[0033] When the common voltage Vcom' of the input differential
voltage pair DIN and DIP is not lower than the reference voltage
Vr', the input circuit 310 directly transfers the input
differential voltage pair DIN and DIP as the input differential
voltage pair DIN' and DIP' to the output circuit 320 without
pulling the input differential voltage pair DIN' and DIP' up. The
output circuit 320 then takes the input differential voltage pair
DIN' and DIP' and pulls the output voltage Vo1' high or low.
[0034] The detailed description of the input circuit 310 is
explained as follows. In the input circuit 310, when the common
voltage Vcom' is lower than the reference voltage Vr', the switches
363 and 364 are turned on to transmit the input differential
voltage pair DIN and DIP to the source followers 342 and 341 in the
level adjustment circuit 340, respectively. Meanwhile, the switches
361 and 362 are turned off. The transistors 346 and 344 in the
source followers 342 and 341 then pulls the voltages DIN and DIP
up, respectively, by amounts equal to the gate-drain cross voltages
of the transistors 346 and 344. The pulled-up input differential
voltage pair DIN' and DIP' is then transferred to the first stage
amplifier 370 in the output circuit 320.
[0035] In the input circuit 310, when the common voltage Vcom' is
not lower than the reference voltage Vr', the switches 361 and 362
are turned on to transmit the voltage DIN and DIP as the voltage
DIN' and DIP' directly to the output circuit 320. Meanwhile, the
switches 363 and 364 are turned off, so that the level adjustment
circuit 340 will not receive the input differential voltage pair
DIN and DIP.
[0036] In the output circuit 320, the first and second stage
amplifiers 370 and 380 are both powered by the same supply voltage,
for example, one of the high and low supply voltages HVDD and LVDD.
The functions of transistors 371 to 373 in the first stage
amplifier 370 in FIG. 3 are similar to the function of the
transistors 271 to 273 in the first stage amplifier 270 in FIG. 2,
respectively. The functions of the transistors 381 to 384 are
similar to those of the transistors 281 to 284, respectively. The
corresponding transistors in the output circuits 320 and 220 are
complementary. For example, the transistor 371 is NMOS, while its
corresponding transistor 271 is PMOS. The function of the inverter
390 is similar to that of the inverter 290.
[0037] In the output circuit 320, the drain-source cross voltage of
the transistor 371 is Vds, and the gate-source cross voltage of the
transistors 372 and 373 are Vgs. When the common voltage of the
input differential voltage pair DIN' and DIP' is lower than the
voltage equal to Vds+Vgs, the transistors 372 and 373 will be cut
off, which causes the output circuit 320 to be disabled. Therefore,
by applying the input circuit 310, which pulls up the input
differential voltage pair DIN and DIP when the common voltage Vcom'
of the input differential voltage pair DIN and DIP is too low, the
transistors 372 and 373 therefore receive the pulled-up input
differential voltage DIN' and DIP' so as to be kept turned on.
[0038] Consequently, even if the common voltage Vcom' of the input
differential voltage pair DIN and DIP is too low, the common
voltage of the input differential voltage pair DIN' and DIP'
produced by the input circuit 310 will not be lower than the
voltage Vds+Vgs, so that the output circuit 320 works properly.
Thus, the preamplifier 300 according to the second embodiment is
capable of properly preamplifying the input differential voltage
pair even with wide range of common voltage.
[0039] While the invention has been described by way of example and
in terms of a preferred embodiment, it is to be understood that the
invention is not limited thereto. On the contrary, it is intended
to cover various modifications and similar arrangements and
procedures, and the scope of the appended claims therefore should
be accorded the broadest interpretation so as to encompass all such
modifications and similar arrangements and procedures.
* * * * *