1. Electronics - Revision 2. In electronics, it is the voltage that is important. Draw voltage time graphs for analogue and digital systems. 3. Draw a block diagram for a public address system. 4. Why do we need an amplifier in the system ? 5. What is the voltage gain of an amplifier ? 6. What is the gain of an amplifier which has input voltage of 2V and output voltage of 8V ? 7. What does an amplifier do to the frequency of the signal ? 1. Copy and complete the three blocks which make up an electronic system. Tutorial Questions page 72 Qu 1 to 6

2. Operational amplifiers (op amps) are multistage amplifiers and can give high gain with very little distortion. Fortunately we don’t have to know how they operate – just how they can be used. _+_+ Inverting input Non-inverting input output Circuit symbol

3. Connecting the power supply 2 x 9V batteries V out Adjust the offset control until V out = 0 this balances the batteries

4. The Op Amp – Inverting Mode, d.c. Vo V1V1 -+-+ RfRf R1R1 V1V1 VoVo 0V +Vsupply Feedback resistor

5. The Op Amp – Inverting Mode, d.c. R1()R1()R f (  ) V 1 (V)V O (V)V gain R f /R 1 100k 0.5 10k100k0.5 100k10k0.5 100k1M0.5 1M100k0.5 10k1M0.5 Vo V1V1

6. Op Amp in inverting mode V o = - R f V 1 R 1 Tutorial Questions page 74 Qu 9 Revision Ex 5.1

7. Uses of an op amp in inverting mode Inverting (changing +/-) Multiplication (amplifying) Addition Binary/digital converter Making square waves Try the experiments showing these. Tutorial question p73 Qu 8, 10 to15 Revision Ex 5.2 and 5.3

8. Op Amp Differential Mode R2 R1RfRf V out -+-+ RfRf R1R1 V1V1 VoVo R3R3 R2R2 V2V2 +Vsupply

9. R1 = R2 = R3 = Rf = 10k  V1V1 V2V2 VoVo 0.60.4 1.00.4 0.31.0 0.61.0 1.80.6 - 0.2 -0.6 0.7 0.4 -1.2 V o = V 2 – V 1

10. R1 = R2 = 10k  Rf = R3 = 100k  V1V2Vo 1.01.1 2.02.2 0.60.8 0.70.5

11. Op amp in the differential mode. Vo = (V 2 – V 1 ) R f R 1 The op amp finds the difference between the two inputs ie subtracts them. It then amplifies this difference. Tutorial questions p 76 Qus 16 to 21 Rev Qus Ex 5.4 and 5.6 For higher Rf R 3 R 1 R 2

12. NPN transistorPNP Transistor b +0.7 V e at 0V c connected to +Vs b - 0.7V c connected to - Vs e at 0V b base c collector e emmitter I I