V to I Buffer for Bias Reference Currents Yusuf Matcheswala May 08, 2009
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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
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