Transcript High Gain Transimpedance Amplifier with Current

High Gain Transimpedance Amplifier
with Current Mirror Load
By:
Mohamed Atef
Electrical Engineering Department
Assiut University
Assiut, Egypt
Outline
• Nanometer CMOS Optical Receivers
• High Gain TIA with Current Mirror Load
• Post Amplifiers and Output Driver
• Simulation Results
• Conclusions
Outline
• Nanometer CMOS Optical Receivers
• High Gain TIA with Current Mirror Load
• Post Amplifiers and Output Driver
• Post Layout Simulation Results
• Conclusions
Nanometer CMOS Optical Receivers
 The TIA is the most critical building block at the optical receiver side in an
optical communication system.
 CMOS silicon integrated circuits appear to be the best technology that can
achieve the required level of integration with reasonable speed, cost, and yield.
 As CMOS technology is downscaled, the peak transit frequency of the transistors
is increased.
 However, the supply voltage of nanometer CMOS chips must be decreased
to prevent destructive breakdown in the MOSFETs and to save power in digital
circuits.
 Also, the transistor output resistance decreased with down scaling the
transistors, as a result the intrinsic voltage gain of a transistor will be smaller.
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Nanometer CMOS Optical Receivers
Therefore, Multistage TIA is needed for high-gain high-speed amplifiers, which
increase the overall power consumption and may affect the amplifier stability.
 The CS-TIA sensitivity essentially depends on the input-node capacitance, the
transconductance of the input transistors, and therefore the current through
them, has to be maximized for minimum noise.
The proposed TIA employs a CS amplifier with a current mirror active load to
achieve a high gain and bandwidth at low power consumption.
The proposed TIA employs an CS amplifier with a current mirror active load to
achieve a higher gain at lower power consumption than with the normal CS-TIA.
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Outline
• Nanometer CMOS Optical Receivers
• High Gain TIA with Current Mirror Load
• Post Amplifiers and Output Driver
• Simulation Results
• Conclusions
High Gain TIA with Current Mirror Load
Fig.1. Common source TIA with shunt feedback resistor and current mirror load
High Gain TIA with Current Mirror Load
The transimpedance gain transfer function of the TIA in Fig.1 is given by the following relation:
High Gain TIA with Current Mirror Load
The transimpedance gain transfer function of the TIA in Fig.1 is given by the
following relation:
For low frequency the transimpedance gain is
As the PD capacitance is larger than the other capacitances (); the bandwidth
is determined by the input dominant pole:
Outline
• Nanometer CMOS Optical Receivers
• High Gain TIA with Current Mirror Load
• Amplifiers and Output Driver
• Post Layout Simulation Results
• Conclusions
Post Amplifiers and Output Driver
Fig.2. Single ended to differential converter, differential post amplifier and output driver
High Gain TIA with Current Mirror Load
The differential output stage is preferred over a single-ended one due to its
higher rejection to common mode and power supply noise.
The TIA’s output (single-ended) is fed to the input of single ended to differential
the converter (M1 and R1). The second input of the single-ended to differential
converter is biased through a low-pass filter (Cs and Rs) coming from the TIA
output.
The next stage after the first differential post amplifier is a pre-driver stage (M2
and R2) to increase the gain and make the interface to the 50Ω driver.
The last stage in the optical receiver is a 50 Ω differential output driver (M3 and
R3 = 50 Ω) to make the interface between integrated optical receiver chip and the
measurement setup.
Outline
• Nanometer CMOS Optical Receivers
• High Gain TIA with Current Mirror Load
• Post Amplifiers and Output Driver
• Simulation Results
• Conclusions
Simulation Results
The proposed optical receiver has been integrated in a 130nm CMOS technology
with one single supply voltage 1.8V.
The optical receiver is optimized for an off-chip large area photodiode with 1.3pF
capacitance and a responsivity of 1 A/W.
The ESD protection and input pad have together a 700fF capacitance. The
bonding wires are modeled by 0.7nH inductors. The proposed current mirror load
TIA consumes 2.1mA.

The simulated frequency response of the TIA obtained is shown in Fig. 3. The
TIA has a bandwidth equal to 1.05 GHz. The transimpedance gain is 64.5 dBΩ
Simulation Results
The simulated frequency response of the TIA obtained is shown in Fig. 3.
The TIA has a bandwidth equal to 1.05 GHz. The transimpedance gain is 64.5 dBΩ.
Fig. 3. Transimpedance gain for proposed current mirror load TIA.
Simulation Results
The equivalent input noise current density is shown in Fig.4. The average input
referred noise current density is 16pA/√Hz and the integrated input referred noise
current is 682nA.
Fig. 4. Input noise current density for proposed current mirror load TIA.
Simulation Results
A sensitivity of -20.3 dBm is obtained for the presented optical receiver for BER=1012 at a data rate of 1.25 Gbit/s. Figure 5 shows the eye diagram at 1.25 Gbit/s with
PRBS=215-1 and an input photodiode current of 9.3µA.
Fig. 5. Eye diagram at data rate of 1.25Gbit/s with PRBS = 215 – 1 and 9.3 µA
peak to peak input photodiode current
Simulation Results
The transimpedance bandwidth and gain are calculated for 1000 runs, see Fig. 6.
The mean (µ) value of the transimpedance gain is calculated to be 64.44 dBΩ with
standard deviation (ϭ) of 1.41 dBΩ, and bandwidth mean value is 1.055 GHz with
standard deviation of 83.27 MHz.
Fig. 6. Monte-Carlo simulation for proposed current mirror load TIA (a) Transimpedance gain (b) Bandwidth
Simulation Results
Table I: Comparison with recently published Gigabit implemented CMOS technology
Conclusions
 A 1.25 Gb/s high gain transimpedance amplifier in 130 nm
CMOS is presented.
 The presented TIA shows a 682nA integrated input
referred noise current and 3.78 mW power consumption.
 The introduced current mirror load TIA shows a high
performance compared to the conventional TIAs due to the
higher gain coming from the current mirror active load.
 By using the active load TIA an optical receiver with higher
bandwidth and sensitivity can be designed at low power
consumption
Mohamed Atef
Electrical Engineering Department
Assiut University
[email protected]
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