V to I Buffer for Bias Reference CurrentsYusuf Matcheswala

May 08, 2009

Electrical specifications

• Conditions for in-spec operation:– 3.0V ≤ VDD ≤ 3.6V– Temperature: -40C to 150C– Reference voltage: 500mV

• Design goals– Good regulation.– Good PSRR.– Better than 60 degree phase margin for good stability.– Low quiescent current.

Device Parameters

File: top_params.pdf

REF node

Voltage at this node tracks REF node

Matched

Buffer

File: amp_params.pdf

Input Level Shifters

Folded cascode

Common source output stage

Bias stage

Tail current sink

Miller compensation

NMOS load

Current Mirror

File: bias_params.pdf

Cascode device

Bias device

Current source for buffer

File: cs_params.pdf

Iptat

DC analysis

Simulation setup(mos=ss, bipolar=s res=s, -40C, 3.0V)

File:top_ssss_m40C_3p0.pdf

6uA

3uA

501.6mV

500mV

Buffer(mos=ss, bipolar=s res=s, -40C, 3.0V)

File:amp_ssss_m40C_3p0.pdf

1.5uA

6uA

2.3uA

Current mirror (mos=ss, bip=s res=s, -40C, 3.0V)

File:bias_ssss_m40C_3p0.pdf

6uA 3uA

Current source for buffer(mos=ss, bipolar=s, res=s, -40C, 3.0V)

File:cs_ssss_m40C_3p0.pdf

4.7uA4.8uA

AC/Stability analysis

PM GM(dB)

MOS ss,

Bipolar s, Resistor ss,

-40C, VDD=3.0V

101.2 16.4

MOS ff, Bipolar=f, Resistor ff, 150C, VDD=3.0V

86.9 37.8

Nominal 116.0 25.4

Stability summary

Stability response

File:loopgain.pdf

miller compensation cap adds a zero.

PSRR

File:psrr.pdf

Transient analysis

File:trans.pdf

No ringing, smooth transitions on buffer output

Pulse on Vref node

Conclusions

• Good stability over process and temperature.• Good regulation over process and temperature.• PSRR

– ~-47dB upto 200KHz– ~-39dB upto 6MHz

• Low buffer quiescent current (~35uA-80uA)

End of main presentation

Additional slides

Simulation setup(mos=ff, bip=f res=f, 150C, 3.0V)

Iin=20.18uA

Iref1=10.1uA

Vfb=499.76mV

Vref1=500.76mV

File:top_ffff_150_3p0.pdf

V to I Buffer (mos=ff, bip=f res=f, 150C, 3.0V)

File:amp_ffff_150_3p0.pdf

Current mirror (mos=ff, bip=f res=f, 150C, 3.0V)

File:bias_ffff_150_3p0.pdf

Current source for buffer (mos=ff, bip=f res=f, 150C, 3.0V)

Iin=20.72uA

Iptat=11.25uA

File:cs_ffff_150_3p0.pdf

V to I buffer(mos=sf, bipolar=s res=s, -40C, 3.0V)

File:amp_sfss_m40C_3p0.pdf