The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1st year undergraduate programme.
The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.
3. Generalised feedback configuration Amplifier Forward Gain A Feedback Network ß Loop Gain A x ß Close Loop Gain Amplifiers with Feedback Vin Vout Va ß A
4. Advantages Gain Sensitivity Bandwidth Disadvantages Gain Reduction Possible Instability Today we will look at the way that the feedback is applied. There are four possible configurations (topologies): Voltage-Series Feedback (voltage amplifier) Current-Series Feedback (transconductance amplifier) Current Shunt Feedback (current amplifier) Voltage –Shunt Feedback (transresistance amplifier)
5. There are two parts First part - voltage or current - this tells us how the output is sampled and hence the output of the amplifier. Voltage is sampled in parallel and Current is sampled in series. Second part – series or shunt – this tells us how the feedback is applied to the input. Series is feeding back voltage to be subtracted and Shunt is feeding back current which is subtracted. Amplifiers with Feedback
6. Voltage Series Feedback Amplifiers with Feedback + Va - + Vf - + Vin - + Vout - Voltage Amplifier Rin Rout AVa Feedback ß
7. Finally Series connection on the input, increases input resistance. Input Resistance Resistance looking into the input is R IN , the input current is Iin. Amplifiers with Feedback
8. Output Resistance Resistance looking in on the output is R OUT . Iout is the current flowing in on the output. No input applied. Voltage (parallel) sampling on the output decreases the output resistance. Amplifiers with Feedback
9. Current Series Feedback Amplifiers with Feedback + Va - + Vf - + Vin - Transconductance Amplifier Rin Rout AVa Feedback ß Iout
10. Input Resistance As the feedback is applied in the same way as the previous topology the effect is the same i.e. resistance increases. Amplifiers with Feedback
11. Output Resistance Resistance looking in on the output is R OUT . Vout is the voltage across the output. No input applied. Current (series) sampling on the output increases the output resistance. Amplifiers with Feedback
12. Current Shunt Feedback Amplifiers with Feedback Ia If Iin Current Amplifier Rin Rout AIa Feedback ß Iout
13. Input Resistance Resistance looking into the input is R IN , the input voltage is Vin. Finally Shunt (parallel) connection on the input, decreases input resistance. Amplifiers with Feedback
14. Output Resistance As the sample is derived in the same way as the previous topology the effect is the same i.e. resistance increases. Amplifiers with Feedback
15. Voltage Shunt Feedback Amplifiers with Feedback Ia If Iin Transresistance Amplifier Rin Rout AIa Feedback ß + Vout -
16. Input Resistance As the feedback is applied in the same way as the previous topology the effect is the same i.e. resistance decreases. Output Resistance As the sample is derived in the same way as the first topology the effect is the same i.e. resistance decreases. Amplifiers with Feedback
17. Summary In each case when feedback is applied the input and output resistance become more ideal for that particular amplifier. Amplifiers with Feedback Topology Voltage series Current series Current shunt Voltage shunt Parameter Gain decrease decrease decrease decrease Bandwidth increase increase increase increase Input Resistance increase increase decrease decrease Output Resistance decrease increase increase decrease