Design of Low Power Instrumentation Amplifier

Instrumentation Amplifier

Design Goal I want to design an amplifier with more than 40 dB in Gain Less than 10 uA of current

Top Level Schematic 1 st stage amplifier 2 nd stage Bias circuit

Design Strategy Get a voltage gain of 10 from the first stage (By choosing R1 and RG carefully) Get the rest of the gain from the second stage Reuse amplifier cell

Active Loaded Differential Amplifier 2 uA of current Voltage gain of 24.56

Biasing of M3 2 uA of current

Testing of the ECG Circuit (Biasing Circuit)

Low Voltage Cascode Bias Cicuit To keep M2 in saturation: V x >V b -V th →V x +V th2 >V b To keep M1 in saturation: V A >V x -V th1 Since V A =V b -V GS2, V b >V x -V th1 +V GS2 Design criteria for M2

Vb Requirement Vb=VOD3+VGS4 to produce a minimum output Voltage of VOD3 and VOD4. By design, VGS4=VGS2, VA=VB Vb=V OD2 +V TH2 +V OD1.

Vb Generation Requirement: Vb=V OD2 +V TH2 +V OD1 V GS5 =V GS2 V OD1 =V GS6 -V TH7 Problem: M5 suffers from no body effect M2 suffers from body effect Design M7 (Large W 7 /L 7 ) so that VGS7 is approx. VTH7 Need to have sufficiently large VGS6, otherwise M6=triode since M7=Sat.

Testing of the ECG Circuit (Biasing Circuit)

Biasing Circuitry

Top Level Schematic 1 st stage amplifier 2 nd stage Bias circuit 2 uA

Gain of the Amplifier

Trasient Simulation Vin,diff=2 mV Vout,single=336 mV Vout,single/Vin,diff=168