Switched Capacitor Blocks Alex Doboli, Ph.D. Department of Electrical and Computer Engineering State University of New York at Stony Brook Email: adoboli@ece.sunysb.edu ©Alex Doboli 2006

Overview of the Chapter Introduction to SC circuits Programmable SC blocks in PSoC SC principle: controlled movement of charge Electrical nonidealities: circuit nonidealities, non-zero switch resistance, channel charge injection, clock feedthrough Basic SC blocks: gain amplifier, programmable gain amplifier, comparator, integrator, differentiator PSoC’s programmable SC blocks: Type C and Type D SC blocks Programming (registers) ©Alex Doboli 2006

Introduction to SC Techniques Integrated capacitors are easier to fabricate than resistors Average resistance approximated through charge movement I = V / R Q = C V Iaverage = Q fs = C V fs => Req = 1 / C fs ©Alex Doboli 2006

Introduction to SC Techniques Constraints: Switches Ф1 and Ф2 can never be closed at the same time Switch Ф1 must have time to open before switch Ф2 closes Switch Ф2 must have time to open before switch Ф1 closes Frequency fs must allow enough time for the circuits to fully charge and discharge ©Alex Doboli 2006

Non-idealities in SC Circuits Non-zero on-resistance of MOSFETs: d Vc(t) / d t = ID(t) / C Linear: d Vc(t) / d t = m Cox W [(VDD – Vc(t) - Vth)(Vin – Vc(t)) – (Vin – Vc(t))2 / 2] / 2 LC Vc(t) = (2 K exp (A Vin t) – A exp (A Vin t) + exp (kt + K[1])) Vin / (A exp (A Vin t) + exp (K t + K[1]) A = m Cox W / 2 L C K = A (VDD – Vth) Saturation:d Vc(t) / d t = m Cox W [(VDD – Vc(t) - Vth)(Vin – Vc(t)) – (Vin – Vc(t))2 / 2] / 2 LC Vc(t) = [(A t – C[1]) (VDD - Vth) - 1] / (A t – C[1]) Vc(0) = 0 => C[1] = - 1 / (VDD - Vth) Vc(t) = VDD – Vth – 1 / (a t – C[1]) ©Alex Doboli 2006

Non-idealities in SC Circuits Channel charge injection: Qchannel = W L Cox (VDD – Vin - Vth) D Vc = W L Cox (VDD – Vin - Vth) / C Trade-offs: Accuracy vs. speed (small W helps accuracy but decreases speed) ©Alex Doboli 2006

Non-idealities in SC Circuits Clock feedthrough: Capacitive coupling through Cgd D Vout = - Cgd,2 D VΦ2 Trade-offs: Accuracy vs. speed (small W lowers coupling but lowers speed too) ©Alex Doboli 2006

SC Fixed Gain Amplifier Characteristics: acquisition phase transfer phase ©Alex Doboli 2006

Acquisition & Transfer Phase Q = Vin CA Vout = - D Q / CF Gain = - CA / CF ©Alex Doboli 2006

Autozero Adjustment QAi = Voffset CA QAi + QFi = QAf + QFf QFi = Voffset CF QAf = (Vin – Voffset) CA QFf = (Voffset – Voutf) CF QAi + QFi = QAf + QFf Voutf = Voffset – [(CA + CF) Voffset – CA(Voffset - Vin)] / CF Voutf = - CA / CF Vin ©Alex Doboli 2006

SC Selectable Gain Polarity Amplifier ©Alex Doboli 2006

SC Comparator ©Alex Doboli 2006

SC Integrator ©Alex Doboli 2006

SC Differentiator ©Alex Doboli 2006

Improved Reference Selection ©Alex Doboli 2006

Two Bit ADC ©Alex Doboli 2006

Analog to Digital Conversion ©Alex Doboli 2006