Switched-Capacitor Circuits - University of Toronto
Switched-Capacitor Circuits - University of Toronto
Switched-Capacitor Circuits - University of Toronto
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Charge Injection Example<br />
• Estimate dc <strong>of</strong>fset due to channel-charge injection<br />
when = 0 and C2 = CA = 10C3 = 10pF.<br />
C 1<br />
• Assume switches Q3 Q4 have Vtn = 0.8V,<br />
W = 30m ,<br />
L = 0.8m , Cox 1.9 10 , and power<br />
supplies are .<br />
• Channel-charge <strong>of</strong> (when on) is<br />
3 –<br />
= pF m 2<br />
<br />
2.5V<br />
Q3 Q4 QCH3 = QCH4 = – 300.80.00192.5 – 0.8<br />
– 77.5 10 3 –<br />
= pC<br />
• dc feedback keeps virtual opamp input at zero volts.<br />
<strong>University</strong> <strong>of</strong> <strong>Toronto</strong><br />
Charge Injection Example<br />
• Charge transfer into given by<br />
• We estimate half channel-charges <strong>of</strong> Q3, Q4 are<br />
injected to the virtual ground leading to<br />
1<br />
--Q 2 CH3 + QCH4 which leads to<br />
= QC3 <strong>University</strong> <strong>of</strong> <strong>Toronto</strong><br />
Q C3<br />
C 3<br />
=<br />
– C3vout<br />
(59)<br />
47 <strong>of</strong> 60<br />
© D. Johns, K. Martin, 1997<br />
(60)<br />
(61)<br />
77.5 10<br />
vout (62)<br />
• dc <strong>of</strong>fset affected by the capacitor sizes, switch sizes<br />
and power supply voltage.<br />
3 –<br />
pC<br />
= ------------------------------------ =<br />
78 mV<br />
1pF<br />
48 <strong>of</strong> 60<br />
© D. Johns, K. Martin, 1997
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