U.S. patent application number 15/425262 was filed with the patent office on 2018-08-09 for high swing transmitter driver with voltage boost.
The applicant listed for this patent is Euhan Chong, Yingying Fu. Invention is credited to Euhan Chong, Yingying Fu.
Application Number | 20180227001 15/425262 |
Document ID | / |
Family ID | 63014014 |
Filed Date | 2018-08-09 |
United States Patent
Application |
20180227001 |
Kind Code |
A1 |
Chong; Euhan ; et
al. |
August 9, 2018 |
HIGH SWING TRANSMITTER DRIVER WITH VOLTAGE BOOST
Abstract
A transmitter driver is disclosed. The transmitter driver
includes first and second voltage mode drivers and a secondary data
path. The secondary data path is connected in parallel with the
first and second voltage mode drivers. A high frequency booster
provides a high frequency path for boost current from the current
source, to enable a high frequency voltage boost at the output
ports.
Inventors: |
Chong; Euhan; (Ottawa,
CA) ; Fu; Yingying; (Toronto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chong; Euhan
Fu; Yingying |
Ottawa
Toronto |
|
CA
CA |
|
|
Family ID: |
63014014 |
Appl. No.: |
15/425262 |
Filed: |
February 6, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 25/0298 20130101;
H04L 25/0272 20130101; H04L 27/04 20130101 |
International
Class: |
H04B 1/04 20060101
H04B001/04; H03K 17/687 20060101 H03K017/687; H04L 27/04 20060101
H04L027/04; H04L 25/02 20060101 H04L025/02 |
Claims
1. A transmitter driver comprising: a first voltage mode driver
coupled to receive a first differential input signal from a first
input port of the transmitter driver, and coupled to provide a
first differential output signal at a first output port of the
transmitter driver; a second voltage mode driver coupled to receive
a second differential input signal from a second input port of the
transmitter driver, and coupled to provide a second differential
output signal at a second output port of the transmitter driver; a
secondary data path having first input and output ports connected
in parallel with the first voltage mode driver, and having second
input and output ports connected in parallel with the second
voltage mode driver, the secondary data path receiving boost
current from a current source; and a high frequency booster
connected to the first and second input ports of the transmitter
driver, and connected between the current source and the secondary
data path, the high frequency booster providing a high frequency
path for the boost current from the current source.
2. The transmitter driver of claim 1, wherein the high frequency
booster comprises: a respective RC network connected to each of the
first and second input ports of the transmitter driver to provide
the high frequency path, each of the respective RC network
connected to each of the first and second input ports of the
transmitter driver including a feedforward capacitor and a
resistor.
3. The transmitter driver of claim 2, wherein the resistor of each
of the respective RC network connected to each of the first and
second input ports of the transmitter driver is a variable
resistor.
4. The transmitter driver of claim 3, wherein resistance of each of
the variable resistor of the respective RC network connected to
each of the first and second input ports of the transmitter driver
is controllably variable in the range of about 0 ohms to about 1000
ohms.
5. The transmitter driver of claim 2, wherein capacitance of each
of the feedforward capacitor of the respective RC network connected
to each of the first and second input ports of the transmitter
driver is in the range of about 10 femtofarad (fF) to about 100
fF.
6. The transmitter driver of claim 2, wherein each of the
feedforward capacitor of the respective RC network connected to
each of the first and second input ports of the transmitter driver
is a variable capacitor.
7. The transmitter driver of claim 1, further comprising: a first
set of control switches connected to the high frequency booster to
enable or disable the high frequency path.
8. The transmitter driver of claim 7, further comprising: a second
set of control switches connected to the secondary data path to
enable or disable receiving of the boost current.
9. A transmitter for transmitting differential signals, comprising:
a transmitter driver comprising: a first voltage mode driver
coupled to receive a first differential input signal from a first
input port of the transmitter driver, and coupled to provide a
first differential output signal at a first output port of the
transmitter driver; a second voltage mode driver coupled to receive
a second differential input signal from a second input port of the
transmitter driver, and coupled to provide a second differential
output signal at a second output port of the transmitter driver; a
secondary data path having first input and output ports connected
in parallel with the first voltage mode driver, and having second
input and output ports connected in parallel with the second
voltage mode driver, the secondary data path receiving boost
current from a current source; and a high frequency booster
connected to the first and second input ports of the transmitter
driver, and connected between the current source and the secondary
data path, the high frequency booster providing a high frequency
path for the boost current from the current source; and a processor
coupled to the transmitter driver for controlling operation of the
transmitter driver.
10. The transmitter of claim 9, wherein the high frequency booster
comprises: a respective RC network connected to each of the first
and second input ports of the transmitter driver to provide the
high frequency path, each of the respective RC network connected to
each of the first and second input ports of the transmitter driver
including a feedforward capacitor and a resistor.
11. The transmitter of claim 10, wherein the resistor of each
respective RC network connected to each of the first and second
input ports of the transmitter driver is a variable resistor, and
wherein the processor is coupled to control resistance of each
variable resistor.
12. The transmitter of claim 11, wherein resistance of each of the
variable resistor of the respective RC network connected to each of
the first and second input ports of the transmitter driver is
controllably variable in the range of about 0 ohms to about 1000
ohms.
13. The transmitter of claim 10, wherein capacitance of each of the
feedforward capacitor of the respective RC network connected to
each of the first and second input ports of the transmitter driver
is in the range of about 10 femtofarad (fF) to about 100 fF.
14. The transmitter of claim 10, wherein each of the feedforward
capacitor of the respective RC network connected to each of the
first and second input ports of the transmitter driver is a
variable capacitor, and wherein the processor is coupled to control
capacitance of each variable capacitor.
15. The transmitter of claim 9, further comprising: a first set of
control switches connected to the high frequency booster to enable
or disable the high frequency path; wherein the processor is
coupled to turn on or off the first set of control switches.
16. The transmitter of claim 15, further comprising: a second set
of control switches connected to the secondary data path to enable
or disable receiving of the boost current; wherein the processor is
coupled to turn on or off the second set of control switches.
17. The transmitter of claim 9, wherein the transmitter is coupled
to a receiver via differential communication lines.
Description
FIELD
[0001] The present disclosure is related to transmitter drivers, in
particular transmitter drivers for high speed transmission.
BACKGROUND
[0002] Pulse amplitude modulation (PAM) is a form of signal
modulation where bit values are encoded in the amplitude of signal
pulses. PAM4 is a form of PAM in which four distinct amplitude
levels are used, each amplitude level encoding a different
combination of two bits. PAM4 signaling has shown promise for high
speed signaling (e.g., greater than 56 Gbps), compared to
non-return to zero (NRZ) signaling.
[0003] A challenge of PAM4 signaling, compared to NRZ signaling, is
that in PAM4 signaling the signal swing is decreased by 1/3 (or 9.5
dB) compared to NRZ signaling. This is even more problematic when
considering technologies that require low power supplies and low
breakdown voltages. In addition, bandwidth limitation at high data
rates (e.g., greater than 56 Gbps) has been found to degrade the
vertical eye opening in the eye diagram.
[0004] There have been attempts to increase the output swing using
a high efficiency voltage mode driver in combination with a current
mode logic (CML) current boost circuit. However, the increase to
voltage swing achieved in these attempts may not be sufficient,
particularly at high frequencies (e.g., greater than 56 Gbps). A
finite impulse response (FIR) filter may be used to provide some
voltage boost, however this requires significant power and physical
area to implement. The use of a FIR filter may also be limited by
the number of taps that must be implemented.
SUMMARY
[0005] The present disclosure describes a circuit for increasing
the bandwidth of a transmitter driver, without directly loading the
transmitter output.
[0006] A continuous time high-pass filter response is added to the
transmitter output, using an AC-coupled feed-forward path. The
capacitor-coupled path causes the voltage at the current source to
change, such that more current is injected to the output at data
transmission. This additional current helps to boost the voltage of
high frequency signals, and has little or no effect on low
frequency signals.
[0007] In some examples, the transmitter driver includes control
switches to enable the bandwidth to be adapted for different data
rates.
[0008] According to a first aspect of the invention, there is
described, a transmitter driver comprising a first voltage mode
driver coupled to receive a first differential input signal from a
first input port of the transmitter driver, and coupled to provide
a first differential output signal at a first output port of the
transmitter driver. The driver further comprises a second voltage
mode driver coupled to receive a second differential input signal
from a second input port of the transmitter driver, and coupled to
provide a second differential output signal at a second output port
of the transmitter driver. The driver further comprises a secondary
data path having first input and output ports connected in parallel
with the first voltage mode driver, and having second input and
output ports connected in parallel with the second voltage mode
driver, the secondary data path receiving boost current from a
current source. Also, the driver comprises a high frequency booster
connected to the first and second input ports of the transmitter
driver, and connected between the current source and the secondary
data path, the high frequency booster providing a high frequency
path for the boost current from the current source.
[0009] According to a second aspect of the invention, there is
described a transmitter for transmitting differential signals,
comprising a transmitter driver including a first voltage mode
driver coupled to receive a first differential input signal from a
first input port of the transmitter driver, and coupled to provide
a first differential output signal at a first output port of the
transmitter driver. The transmitter also comprises a second voltage
mode driver coupled to receive a second differential input signal
from a second input port of the transmitter driver, and coupled to
provide a second differential output signal at a second output port
of the transmitter driver. The transmitter further comprises a
secondary data path having first input and output ports connected
in parallel with the first voltage mode driver, and having second
input and output ports connected in parallel with the second
voltage mode driver, the secondary data path receiving boost
current from a current source. Still further the transmitter
comprises a high frequency booster connected to the first and
second input ports of the transmitter driver, and connected between
the current source and the secondary data path, the high frequency
booster providing a high frequency path for the boost current from
the current source; and a processor coupled to the transmitter
driver for controlling operation of the transmitter driver.
[0010] According to an implementation of the previous aspects, the
high frequency booster comprises a respective RC network connected
to each of the first and second input ports of the transmitter
driver to provide the high frequency path, each of the RC networks
including a feedforward capacitor and a resistor.
[0011] According to an implementation of the previous
implementation, the resistor of each RC network is a variable
resistor.
[0012] According to an implementation of the previous
implementation, resistance of each variable resistor is
controllably variable in the range of about 0 ohms to about 1000
ohms.
[0013] According to an implementation of any of the previous
implementations, capacitance of each feedforward capacitor is in
the range of about 10 fF to about 100 fF.
[0014] According to an implementation of any of the previous
implementations each feedforward capacitor is a variable
capacitor.
[0015] According to an implementation of any of the previous
implementations, this implementation further comprises a first set
of control switches connected to the high frequency booster to
enable or disable the high frequency path.
[0016] According to an implementation of the previous
implementation, this implementation further comprises a second set
of control switches connected to the secondary data path to enable
or disable receiving of the boost current.
[0017] According to an implementation of the second aspect or any
implementation thereof, the transmitter is coupled to a receiver
via differential communication lines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Reference will now be made, by way of example, to the
accompanying drawings which show example embodiments of the present
application, and in which:
[0019] FIG. 1 is a schematic diagram of an example transmitter and
receiver system for high speed communication;
[0020] FIGS. 2A and 2B are simplified diagrams illustrating effect
of a boost current for a transmitter driver;
[0021] FIG. 3 is a schematic diagram of an example circuit for a
transmitter driver, in which high frequency boost is provided;
[0022] FIG. 4 is a schematic diagram of another example circuit for
a transmitter driver, in which high frequency boost is
provided;
[0023] FIGS. 5A and 5B are plots showing the effects of a high
frequency boost in the example circuit of FIG. 4;
[0024] FIG. 6 is a plot showing the effect of different resistance
values on an output pulse in the example circuit of FIG. 3;
[0025] FIG. 7 is a plot showing the effect of different resistance
values on the rise time of an output pulse in the example circuit
of FIG. 3; and
[0026] FIG. 8 is a plot showing the effect of different resistance
values on the peaking voltage of an output pulse in the example
circuit of FIG. 3.
[0027] Similar reference numerals may have been used in different
figures to denote similar components.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0028] Examples described herein may be implemented in a high speed
(e.g., 56 Gbps or higher) communication system. Other applications
may include other communication systems and transmitters that would
benefit from a transmission boost at high frequencies.
[0029] FIG. 1 is a schematic diagram of an example high speed
communication system 100, including a transmitter 102 and a
receiver 104. The transmitter transmits differential signals to the
receiver over differential communication lines 106. The use of
differential signals may help to reduce the level of noise in
signals received by the receiver 104, particularly where there is
greater distance between the transmitter 102 and the receiver
104.
[0030] In the example shown, the transmitter 102 includes a
transmitter driver 108. Although shown as a single symbol in FIG.
1, the transmitter driver 108 may include more than one circuit
component, as discussed further below. As well, the transmitter 102
may include other components in addition to the transmitter driver
108. The transmitter 102 receives input data signals at transmitter
input ports DO and DOb, and outputs differential signals at
transmitter output ports Tx_m and Tx_p. The differential signals
are transmitted over the differential communication lines 106 and
received by the receiver 104 at receiver input ports Rx_m and
Rx_p.
[0031] To assist in understanding the present disclosure, FIGS. 2A
and 2B are now discussed. FIG. 2A is a simplified diagram
illustrating a source-series-terminated (SST) transmitter driver
200, and FIG. 2B shows the SST transmitter driver 200 with a DC
voltage boost. In FIG. 2A, first and second voltage mode
transmitters 202, 204 are connected to respective resistors Rout_TX
(assuming fixed output resistance). The voltage mode transmitters
202, 204 each receive respective differential input signals, as
shown. The current from each voltage mode transmitter 202, 204 is
I_sst. Far-end termination resistors are shown as Rtermination, and
the output signals of the transmitter driver 200 are the
differential signals at Voutp and Voutm. The peak-to-peak voltage
of the output signals, also referred to as voltage swing, is
limited by the voltage supply (Vsupply) as follows:
Vout_pp = 2 * Rtermination 2 * Rtermination + 2 * Rout_TX * Vsupply
* 2 ##EQU00001##
[0032] To increase the voltage swing, a DC current boost may be
added, as shown in FIG. 2B, where a current source I_boost is
connected to the outputs of each voltage mode transmitter 202, 204.
Thus, the total current the transmitter driver 200 delivers to the
termination resistors Rtermination is I_sst+I_boost. The DC voltage
boost at the output Voutp and Voutm is dependent on the values of
Rout_TX, Rtermination and I_boost. In the case were Rout_TX and
Rtermination have the same resistance R, the voltage swing boost
achieved is 2*I_boost*R. The following table shows example
simulation results demonstrating the effect of I_boost on the
output voltage swing, in the case where Rout_TX and Rtermination
are both 50 ohms and the transmitter driver consumes about 5
mA.
TABLE-US-00001 I_boost (mA) Vswing (Vppd) V_boost (mV) 0 1 0 2.2
1.2 220 3.3 1.3 330
[0033] where Vswing is the peak-to-peak voltage of the voltage
output and V_boost is the additional voltage boost resulting from
I_boost (that is, the additional peak-to-peak voltage of Vswing
provided by I_boost, compared to the case where I_boost is 0 mA).
As noted above, the voltage boost provided is a DC voltage boost,
meaning that it is not specific to high frequency output. Because a
current boost gives rise to an output voltage boost, in the present
disclosure both the terms "current boost" and "voltage boost" may
be used interchangeably, and the term "boost" may be used generally
to refer to both current boost and voltage boost. A high frequency
boost may generally refer to current and voltage boost for high
frequency input signals (e.g., signals at frequencies up to 14
GHz). A high frequency boost may be observed as a transient boost
in signal amplitude at the top of a rise in a pulse signal, and
this boost at the top of a rise may be referred to as
"peaking".
[0034] FIG. 3 shows a schematic diagram of an example circuit 300
for the transmitter driver, in which a high frequency voltage boost
is enabled. The circuit 300 includes first and second voltage mode
transmitters 302, 304 (which may also be referred to collectively
as differential voltage mode transmitters 302, 304) and a secondary
data path 306 connected in parallel.
[0035] The first voltage mode transmitter 302 is coupled to the
input port DO of the transmitter driver, to receive a first
differential input signal, and coupled to the output port Tx_m of
the transmitter driver, to output a first differential output
signal. The second voltage mode transmitter 304 is coupled to the
input port DOb of the transmitter driver, to receive a second
differential input signal, and coupled to the output port Tx_p of
the transmitter driver, to output a second differential output
signal. In the example shown, each of the first and second voltage
mode transmitters 302, 304 includes an inverter 308 and a resistor
310. Each inverter 308 receives input from the input port DO, DOb,
respectively, and is coupled to the output port Tx_m, Tx_p,
respectively, via the respective resistor 310. The resistance value
of each of the resistor 310 may be selected to match the expected
impedance of the transmission line coupled to the output ports
Tx_m, Tx_p. For example, the resistors 310 may each have a
resistance of 50 ohms.
[0036] The secondary data path 306 has first input and output ports
connected in parallel with the first voltage mode transmitter 302,
and second input and output ports connected in parallel with the
second voltage mode transmitter 304. The secondary data path 306
includes a first transistor differential pair, formed by a first
pair of PMOS transistors 312. The gate of each of the PMOS
transistors 312 is connected to the input port DO, DOb,
respectively, and the drain of each PMOS transistor 312 is
connected to the output port Tx_m, Tx_p, respectively. The
secondary data path 306 drives the same output as the voltage mode
transmitters 302, 304. The secondary data path 306 also includes a
second transistor differential pair, formed by a second pair of
PMOS transistors 314. The second pair of PMOS transistors 314 is
connected to transistor current source.
[0037] The secondary data path 306 receives a boost current from a
DC current source 326. The boost current provided by the DC current
source 326 results in a boost at the output ports Tx_m, Tx_p. The
example circuit 300 also includes a high frequency booster 320. The
high frequency booster is connected to the input ports DO, DOb, and
is connected between the current source 326 and the secondary data
path 306. Thus, the current or drive strength of the secondary data
path 306 is determined by the high frequency booster 320. The high
frequency booster 320 provides a high frequency path for the boost
current, enabling a high frequency boost at the output ports Tx_m,
Tx_p. The high frequency booster 320 also enables adjustment of the
high frequency boost, via variable resistors, described below.
[0038] In the high frequency booster 320, the boost current from
the current source 326 is split into two currents to the first pair
of PMOS transistors 312 of the secondary data path 306. The high
frequency path is provided by a RC network for each of the two
differential signals. Each RC network includes a feedforward
capacitor 322 and a variable resistor 324. The feedforward
capacitor 322 is connected between each transmitter input port DO,
DOb and the source terminal of the first pair of PMOS transistors
312. The feedforward capacitor 322 may have capacitance in the
range of about 10 fF to about 100 fF and the variable resistor 324
may have resistance variable between about 0 ohms to about 1000
ohms, for example. The addition of the feedforward capacitors 322
provides a path for additional boost current at high frequencies.
The variable resistors 324 are connected between the feedforward
capacitors 322 and a bias voltage for the PMOS transistors 312. The
variable resistors 324 are controllable (e.g., via a control signal
from a processor (not shown)) to adjust the resistance value of the
variable resistors 324, which may enable adjustment of the settling
time of the boost current. The peaking frequency may be tuned by
adjusting the values of the feedforward capacitors 322 and/or the
variable resistors 324. The resistance of the variable resistors
324 may be adjusted dynamically. Simulation results discussed
further below illustrate how varying the variable resistors 324
affects the output response. The addition of the high frequency
booster 320 introduces relatively little overhead to the circuit
300 for the transmitter driver 108.
[0039] In some examples, the feedforward capacitors 322 may be
variable capacitors, which may be controllable (e.g., via a control
signal from a processor (not shown)) to adjust the capacitance
values. The ability to control and adjust the capacitance values of
the feedforward capacitors 322 may enable additional control of the
high frequency response.
[0040] In some examples, it may be useful to control whether or not
voltage boost should be provided. FIG. 4 is a schematic diagram of
another example circuit 400 for the transmitter driver 108. The
example circuit 400 is similar to the circuit 300 of FIG. 3, with
the addition of control switches 402, 404 to control whether or not
voltage boost at DC and/or high frequency is enabled. The operation
of the control switches 402, 404 may be controlled via control
signals from a processor (not shown), for example. The control
switches 402, 404 may be turned on or off dynamically. The first
set of control switches 402 is provided in the high frequency
booster 320, to control whether there is high frequency boost
provided. When the first set of control switches 402 are all turned
off, the input ports DO, DOb are disconnected from the current
source 326, so input data transitions are not used to control the
current source 326 to increase the high frequency current, and no
high frequency boost is enabled. The second set of control switches
404 is provided at the gates of the first and second pairs of
transistors 312, 314, to control whether there is any voltage boost
provided. When the second set of control switches 404 are all
turned off, the current path for the boost current is open and no
boost current (and hence no voltage boost) is enabled.
[0041] When both sets of control switches 402, 404 are turned off,
no path is provided for the boost current, and the transmitter
driver 108 operates without any voltage boost. When the first set
of control switches 402 is turned off and the second set of control
switches 404 is turned on, only a DC path is provided for the boost
current, and the output of the transmitter driver 108 is provided
with a DC voltage boost, but without high frequency voltage boost.
When both the first and second sets of control switches 402, 404
are turned on, the circuit 400 functions equivalently to the
circuit 300 of FIG. 3, where both DC and high frequency voltage
boost are enabled. When the first set of control switches 402 is
turned on and the second set of control switches 404 is turned on,
the transistors 312, 314 are off and no boost is provided. In some
examples, only the first set of control switches 402 may be
provided, such that the DC voltage boost is always enabled but the
high frequency voltage boost can be enabled or disabled.
[0042] By enabling the selection of whether or not to provide high
frequency boost, independently of whether any DC voltage boost is
enabled, the example circuit 400 may help to lower power
consumption at low data rates, where the benefits of the high
frequency boost may not be needed.
[0043] To help in understanding the present disclosure, some
example simulation results are now discussed. It should be
understood that these simulation results are provided for the
purpose of illustration only, and are not intended to be limiting
or promissory.
[0044] FIGS. 5A and 5B show simulation results for the example
circuit 400 of FIG. 4, with only DC boost (grey solid line) and
with additional high frequency boost (black dotted line). FIG. 5A
shows the current at location ID indicated in FIG. 4, and FIG. 5B
shows the output voltage at output ports Tx_m and Tx_p. As can be
seen in these plots, when high frequency boost is enabled,
additional current is injected when the input signal has a rising
transition, resulting in a transient boost in the output voltage at
the top of each rise.
[0045] FIG. 6 is a plot showing a single pulse of a differential
output voltage of the example circuit 300 of FIG. 3, illustrating
the transient response when the variable resistors are set at
different resistance values. As can be seen from the plot, the
higher the resistance value the greater the high frequency boost
(although this may cause a longer settling time, which may result
in intersymbol interference). The rise time is also shorter for
higher resistance values.
[0046] FIG. 7 is a plot showing the rise time of a single pulse of
a differential output voltage in the example circuit 300 of FIG. 3,
when the variable resistors 324 are set at different resistance
values. As illustrated in FIG. 7, when high frequency boost is
enabled, the rise time may be reduced by up to about 2.2 ps
compared to when no high frequency boost is provided. Thus, the
addition of the high frequency booster may enable quicker output
response, which may be useful for high speed signaling.
[0047] FIG. 8 is a plot showing the peaking voltage of a single
pulse of a 1V differential output voltage in the example circuit
300 of FIG. 3, when the variable resistors 324 are set at different
resistance values. As illustrated in FIG. 8, by varying the
resistance value of the variable resistors 324 from about 200 ohms
to about 1000 ohms, the peaking voltage can be controlled to vary
between about 10 mV to about 75 mV.
[0048] In various examples described herein, a transmitter driver
circuit is described in which the output voltage swing is boosted.
A high frequency booster is added to the conventional transmitter
driver circuit to help improve rise/fall time and help provide a
high frequency boost. The use of variable resistors enables control
of the frequency range at which high frequency boost is provided.
The variable resistors also enable control of rise time and
settling time. In some examples, fixed resistors may be used
instead of variable resistors (e.g., where the ability to
dynamically tune the peaking frequency is not needed). In some
examples, control switches may be added to enable the DC voltage
boost and high frequency voltage boost to be independently enabled
or disabled.
[0049] Compared to other solutions that have been attempted (such
as described by Bassi et al., "3.5 A 45 Gb/s PAM-4 transmitter
delivering 1.3 Vppd output swing with 1V supply in 28 nm CMOS
FDSOI", ISSCC 2016; and Joy et al., "Analog-DFE-based 16 Gb/s
SerDes in 40 nm CMOS that operates across 34 dB loss channels at
Nyquist with a baud rate CDR and 1.2 Vpp voltage-mode driver",
ISSCC 2011), the examples described herein may provide greater
voltage boost at high frequencies (e.g., greater than 56 Gbps).
Further, the example circuits described herein may enable voltage
boost with a smaller overhead and overall smaller size
requirements.
[0050] Although the present disclosure describes examples
implemented in differential transmitters, the present disclosure
may also be adapted for single-ended transmitters (e.g., using only
high frequency booster with only one feedforward capacitor and one
variable resistor).
[0051] Various examples described herein may be used to implement
PAM4 signaling in various high speed communication systems,
including network, storage, computing and mobile systems. The
examples described herein may be applicable to standards for high
speed communication, for both electrical and optical produces.
[0052] Although described in the context of high speed PAM4
signaling, the examples disclosed herein may be useful in other
applications where an output voltage boost, in particular a high
frequency voltage boost, would be desirable.
[0053] The present disclosure may be embodied in other specific
forms without departing from the subject matter of the claims. The
described example embodiments are to be considered in all respects
as being only illustrative and not restrictive. Selected features
from one or more of the above-described embodiments may be combined
to create alternative embodiments not explicitly described,
features suitable for such combinations being understood within the
scope of this disclosure.
[0054] All values and sub-ranges within disclosed ranges are also
disclosed. Also, although the systems, devices and processes
disclosed and shown herein may comprise a specific number of
elements/components, the systems, devices and assemblies could be
modified to include additional or fewer of such
elements/components. For example, although any of the
elements/components disclosed may be referenced as being singular,
the embodiments disclosed herein could be modified to include a
plurality of such elements/components. The subject matter described
herein intends to cover and embrace all suitable changes in
technology.
* * * * *