09_op-amps

Input terminal by v in r2r 1 vout v in v in r2 r1

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: red from op-amp output) voltage drop across R2 is IfR2 = Vin ( R 2 /R1) so that output is higher than neg. input terminal by V in (R2/R 1 ) Vout = V in + V in ( R2 /R1 ) = V in (1 + R 2 /R1) – thus gain is (1 + R2 /R1 ), and is positive – negative sign earns title “inverting” amplifier • Current is sourced from op-amp output in this example • Current is drawn into op-amp output terminal drawn op-amp Winter 2008 9 Winter 2008 10 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Differencing Amplifier Summing Amplifier R2 Rf R1 R1 V1 V R2 V2 + Vout + V+ Vout R1 R2 • Much like the inverting amplifier, but with two input voltages • The non-inverting input is a simple voltage divider: – inverting input still held at virtual ground – I1 and I2 are added together to run through Rf – so we get the (inverted) sum: V out = R f ( V1/R 1 + V 2/R2) – Vnode = V +R 2/(R1 + R 2) • So If = (V • if R2 = R1, we get a sum proportional to ( V 1 + V 2 ) • Can have any number of summing inputs – we’ll make our D/A converter this way Winter 2008 Lecture 9 Vnode)/R1 – Vout = V node IfR2 = V +(1 + R2/R 1)(R2/(R 1 + R2)) – so V out = (R2/R 1)(V + V ) – therefore we difference V + and V 11 Winter 2008 V (R2/R 1) 12 3 Op-Amps 02/14/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Differentiator (high-pass) Low-pass filter (integrator) R C C R Vin Vin + Vout Vout + • For a capacitor, Q = CV, so Icap = dQ/dt = C·dV/dt CV dQ C·dV • If = Vin/R, so C·dVcap/dt = Vin/R /R, C·dV – Thus Vout = IcapR = R C·dV/dt • So we have a differentiator, or high-pass filter – if signal is V0sin t, V out = V 0RC cos t – the -dependence means higher frequencies amplified more – and since left side of capacitor is at virtual ground: d Vout/dt = Vin/RC – so – and therefore we have an integrator (low pass) Winter 2008 13 Winter 2008 14 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 RTD Readout Scheme Notes on RTD readout • RTD has resistance R = 1000 + 3.85 T...
View Full Document

This note was uploaded on 01/30/2014 for the course PHYS 121 taught by Professor Staff during the Winter '08 term at UCSD.

Ask a homework question - tutors are online