EE3B1 – Analogue Electronics

1. EE3B1 – Analogue Electronics Dr. T. Collins T.Collins@bham.ac.uk http://www.eee.bham.ac.uk/collinst/ee3b1

2. EE3B1 Structure • Content Delivery • 18 Lectures (Mondays 12-1, Tuesdays 11-12) • 5 ‘Tutorial’ Sessions (Odd Mondays 4-5) • + revision sessions • Online Material • Tutorial Problems • PowerPoint slides • Circuit analysis walkthroughs • Frequently Asked Questions

3. Analogue Electronics ? Who Cares ? Even digital systems usually rely on analogue electronics in some way. E.g. A “digital” radio: R.F. Pre-Amplifier Power Amplifier D.S.P. Filter

4. Analogue Essentials • Low noise, radio frequency amplifier. • Anti-aliasing filter. • Power amplification. i.e. The module syllabus.

5. Power Amplifiers • Common-emitter amplifiers and operational amplifiers require high impedance loads. • To drive low impedance loads, a power output stage is required. • Designs vary in complexity, linearity and efficiency. • Power dissipation and thermal effects must be considered.

6. Low Noise and R.F. Amplifiers • Pre-amplifier stages are the most prone to noise as the signal level is so low. • Careful design minimises interference. • Common-emitter amplifiers can have a disappointingly low upper cut-off frequency. • Steps can be taken to extend an amplifier’s bandwidth.

7. Active Filters • Passive filter designs consist of a ladder of capacitors and inductors. • Inductors are bulky, expensive and imperfect components – especially when low values are required. • Using operational amplifier designs, inductors can be replaced using a variety of synthesis and simulation techniques.

8. Quiescent Conditions Recap : Common-Emitter Amplifier

9. Biasing 0.12 10 8 Slope = gm 0.11 ic 6 IC Collector Current, [mA] 0.1 vbe 4 0.09 2 VBE 0.08 0 0 0.2 0.4 0.6 0.8 1 0.586 0.590 0.594 0.598 Base-Emitter Voltage [V] Base-Emitter Voltage [V]

10. Small Signal Operation • As vin changes, the base-emitter voltage follows, i.e. vin = vbe. • As vbe changes, the collector current follows, ic = gm.vbe. • As ic changes, the voltage across Rc follows (Ohm’s law). • Gain therefore depends on the relationships between vbe & ic and ic & vout.

11. Mutual Conductance, gm • Mutual conductance, gm, is simply the slope of the IC-VBE curve. • It is not a physical conductance, just the ratio between current and voltage changes. • Since the IC-VBE curve is not a straight line, gm changes with bias current.

12. Voltage Gain

13. Equivalent Circuit

14. Loaded Common-Emitter Amplifier i.e. Low load impedance Þ low gain or high gm. But, high gmÞ low reÞ low rin.

15. Common-Emitter Limitations • It is often not possible to meet a specification using a single amplifier stage • High voltage gain AND high current gain can be incompatible • Solution: Multi-stage amplifiers using: • Differential amplifiers for input • Common-emitter amplifier for voltage gain • Power amplifier for current gain

16. Example – An Operational Amplifier Differential Amp Voltage Amp Power Amp + -

17. Review Topics • Focus on review of 1st and 2nd year material. • In particular • Common-Emitter Amplifier • Small signal analysis • Mutual Conductance • Emitter resistance • etc.