1. Ginsburg/Ogunnika 6.376 Final Presentation1 Adjustable Linear Range Operational Transconductance Amplifier with Noise Compensation Overall topology –Basic WLR with bulk drive, gate degeneration, source degeneration –Variable gain amplifier between drain and gate of the source degeneration transistor to lower source degeneration –Gate of input transistor driven with a weighted sum of its drain (for gate degeneration) and the input voltage –Current steering sets the V L and is compensated to keep noise low Theoretical linear range: –Actual linear range varies from 73mV to 1.25 V N varies from 5.5 to 13.7 Brian Ginsburg, Muyiwa Ogunnika

2. Ginsburg/Ogunnika 6.376 Final Presentation2 Block Diagram 0<A<1 g mb + + gmgm A1-A V in gsgs 1/g mn -A/g mp g mp + i out

3. Ginsburg/Ogunnika 6.376 Final Presentation3 Variable Linear Range Performance Linear range varies from 73mV to 1.248V Each OTA has 45 transistors Common mode input range is from 1.25V to 3 V at highest current levels; increases to 0.85V-3V at low bias current levels In resonant filter, f 90 can vary from 100Hz to 10kHz, and Q can be variable from 1 to 6, though not for all V L

4. Ginsburg/Ogunnika 6.376 Final Presentation4 Stability of the OTA No load capacitor 1kHz bandwidth 100mV linear range Unity-gain feedback <5% overshoot in step response OTA also stable with 10% component mismatch Power with 5pF cap and 10kHz bandwidth <3.47μW

5. Ginsburg/Ogunnika 6.376 Final Presentation5 Circuit Details Variable Gain Amplifier 2I BS k s I LVL k s Gate Drive Weighted Adder I HVL k g I LVL k g

6. Ginsburg/Ogunnika 6.376 Final Presentation6 Noise Impact of V L Variation Observations –For fixed V L, as I B drops, noise improves for fixed I BS –As V L decreases, noise shoots up Solutions –For fixed V L, have I BS =k b I B –Make k b inversely dependent on V L –I BS =(1+6(1-A))I B /20 –Power overhead varies from 30% to 130% Effective number of noise sources from gate drive circuit: Theoretical N vs. V L Actual N vs. V L Dashed: Fixed k b Solid: Variable k b At Q=2, 10kHz –V L =1.25, N=5.4 –21.3μW 0.4dB variation from unity in passband, >50dB attenuation at high frequencies

7. Ginsburg/Ogunnika 6.376 Final Presentation7 Final Layout Fits in less than one quarter of the chip! Most of the additional circuitry is kept very small Conclusions Questions