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.

1. Amplifiers with Feedback Electronic Engineering © University of Wales Newport 2009 This work is licensed under a Creative Commons Attribution 2.0 License .

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

18. This resource was created by the University of Wales Newport and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme. © 2009 University of Wales Newport This work is licensed under a Creative Commons Attribution 2.0 License . The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence. All reproductions must comply with the terms of that licence. The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher. The name and logo of University of Wales Newport is a trade mark and all rights in it are reserved. The name and logo should not be reproduced without the express authorisation of the University. Amplifiers with Feedback