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Analogue Electronics Circuit 2 EKT 214 Chapter 2 Op-Amp Applications and Frequency Response Semester 2 2010/11 By: Norizan Binti Mohamed Nawawi 1 Op-Amp Applications 2.1 Voltage Follower 2.2 Summing Amplifier 2.3 Differencing Amplifier 2.4 Integrator 2.5 Differentiator 2.6 Comparator 2 Voltage Follower / Buffer Amplifier This “buffer” is used to control impedance levels in the circuit – it isolates part of the overall (measurement) circuit from the output (driver). The input impedance to the buffer is very high and its output impedance is low. 3 The output voltage from a source with high output impedance can, via the buffer (voltage follower), supply signal to one or more loads that have a low impedance. Voltage Follower / Buffer Amplifier High input impedance Low output impedance Voltage gain = 1 UNITY GAIN; Vout Av 1 Vin Vout Vin 4 Summing Amplifiers The inverting amplifier can accept two or more inputs and produce a weighted sum. Assuming that V- ≈ 0 (voltage drop at V- is approx. 0). iin The sum of the currents through R1, R2,…,Rn is: iin V V1 V2 ... n R1 R2 Rn Summing Amplifiers The op-amp adjusts itself to draw iin through Rf (iin = if) if if iin V V1 V2 ... n R1 R2 Rn Vout V1 V2 V ... n Rf R1 R2 Rn Rf Rf Rf Vout i f R f V1 V2 ... VN R2 RN R1 The output will thus be the sum of V1,V2,…,Vn, weighted by the Rf Rf Rf , ,..... different gain factors, respectively. R1 R2 R3 Summing Amplifiers Special Cases for this Circuit: 1. If R1 = R2 =……= R then: Vout Rf R1 V1 V2 ..... VN i.e. the output voltage is proportional to the sum of the input voltages (unity gain summing amplifier). 2. If R1 = R2 = … = R and v1, v2, … are either 0V (digital “0”) or 5V (digital “1”) then the output voltage is now proportional to the number of (digital) 1’s input. Example 1 Calculate the output voltage for the circuit below. The inputs are V1 = 50 mV sin(1000t) and V2 = 10 mV sin(3000t). 330 k 33 k _ V1 7 2 Vout 741 10 k V2 3 + 6 4 Answer Vout = - [0.5 sin(1000t) + 0.33 sin(3000t)] 8 Summing Amplifiers Applications Digital to Analog Converter (DAC) • Binary-weighted Resistor DAC (scaling adder) Note: Rf = 8R Summing Amplifiers Applications Digital to Analog Converter • R/2R Ladder DAC Differencing Amplifiers Vout Rf R1 V1 V2 This circuit produces an output which is proportional to the difference between the two inputs. Differencing Amplifiers The circuit is linear so we can look at the output due to each input individually and then add them. Output due to V2 is the same as the inverting amplifier, so: Vout2 Rf R1 V2 The signal to the non-inverting output, is reduced by the voltage divider: Vin Rf R1 R f V1 Differencing Amplifiers The output V1 is that for a non-inverting amplifier: Vout1 R1 R f R1 Vin R1 R f Rf R1 R1 R f V1 Rf R1 V1 Thus the output is: Vout Vout1 Vout2 Vout Rf R1 Rf R1 V1 Rf R1 V2 (V1 V2 ) Thus the amplifier subtracts the inputs and amplifies their difference.