GT AE 6414 - Switched Capacitor Circuits II (23 pages)

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Switched Capacitor Circuits II



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Switched Capacitor Circuits II

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Pages:
23
School:
Georgia Institute of Technology
Course:
Ae 6414 - Multiphase Combustion

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Switched Capacitor Circuits II Dr Paul Hasler Georgia Institute of Technology Basic Switch Cap Integrator C2 1 2 V1 n Vout n GND C1 GND H j C1 C2 Vout n Vout n 1 C1 C2 V1 n Vout z V1 z H z C1 C2 1 1 z 1 1 1 e j T C1 C2 j T assumes T 1 therefore we need to sample much higher factor of 10 to 20 over frequencies of interest Switch Cap Implementation C2 1 2 V1 n Vout n GND C1 GND 1 C2 2 V1 n Vout n GND C1 GND Switch Cap Implementation C2 1 2 V1 n Vout n GND C1 GND Transistor switches result in Parasitic capacitances Charge clock feedthrough Switch Cap Implementation C2 1 2 V1 n Vout n GND C1 C2 GND Now adding Parasitic capacitors 1 Cp4 Cp5 GND 2 GND V1 n Vout n Cp0 Cp1 GND C1 GND GND Cp2 Cp3 GND GND GND Switch Cap Implementation C2 Cp4 1 Cp5 GND 2 GND V1 n Vout n Cp0 Cp1 GND C1 GND GND Cp2 Cp3 GND GND GND Fortunately many of these capacitors have minimal effect on the circuit Parasitic capacitances to a voltage source can be neglected Parasitic capacitances to a virtual AC GND can be neglected the effect of the capacitance is divided by the open loop gain Switch Cap Implementation C2 1 2 V1 n Vout n Cp1 Cp2 C1 GND GND GND GND We still have parasitic capacitances effecting our result We can either make large to swamp out parasitic capacitors or use a stray insensitive design Switch Cap Integrator C2 1 2 V1 n Vout n GND C1 V2 n GND 2 1 We will step through all four phases to get the proper result Switch Cap Integrator 4 n 1 cycle C2 Q C2Vout n 1 V1 n 1 GND C1 V2 n 1 Vout n 1 Voltage remains held Voltage 0V GND This case is important to understand our starting point charge is stored on a capacitor therefore we need to know the initial state Switch Cap Integrator 1 n cycle 1 C2 Q C2Vout n 1 V1 n GND C1 V2 n V1 n GND Charge up the capacitor with voltage V1 n Vout n 1 Output unchanged Switch Cap Integrator 2 n cycle C2 Q1 C1V1 n Q C2Vout n 1 V1 n GND C1 V1 n V2 n GND Q1 C1V1 n We remove the capacitor from the first voltage The voltage is stored across the capacitor Vout n 1



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