Available online
Description
The programme explores some effects of feedback on voltage and current amplifiers, extending these ideas to power amplifiers. In particular, the effects of feedback on the gain bandwidth product of... voltage amplifiers and forms of distortion which feedback cannot improve, are examined.
The programme explores some effects of feedback on voltage and current amplifiers, extending these ideas to power amplifiers. In particular, the effects of feedback on the gain bandwidth product of... voltage amplifiers and forms of distortion which feedback cannot improve, are examined.
| Module code and title: | T283, Introductory electronics |
|---|---|
| Item code: | T283; 04; 1980 |
| First transmission date: | 21-05-1980 |
| Published: | 1980 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:35 |
| + Show more... | |
| Producer: | Ted Smith |
| Contributors: | N. W. Heap; G.(Gaby) Smol |
| Publisher: | BBC Open University |
| Keyword(s): | Amplifiers; Circuits; Voltage amplifiers |
| Footage description: | Gaby Smol, pointing to a simple voltage derived series feedback circuit, introduces the programme. Smol, goes on to perform several experiments with this circuit. Ho looks first at open loop gain and then at two cases with different amounts of feedback. The modulus of gain is plotted against frequency by Nick Heap. He goes on to show from this that negative feedback allows control of gain in an amplifier but also that it may not be possible to obtain, both gain and bandwidth desired in a single amplifier. Gaby Smol explains that amplifier gain can mean not only voltage gain but also power gain. He examines two circuits, one of which has voltage gain and the other a current gain. Smol demonstrates, using a shunt feedback amplifier, that voltage gain is not dependent on the load resistance over a wide range. Smol then demonstrates that with the same circuit, the current gain as opposed to voltage gain, varies greatly with the load. Nick Heap demonstrates a current derived feedback amplifier circuit. He shows that in this circuit, voltage gain changes with the load while current gain is independent over a wide range of loads. Nick Heap summarises the programme so far. He explains that a feedback circuit where voltage gain varies with load resistance and gain is independent of load, is particularly well suited to applications such as magnetic tape recorders. Gaby Smol, with the aid of an oscilloscope and two feedback circuits, discusses the effects of negative feedback on distortion. Finally Nick Heap, with the aid of a circuit diagram, briefly describes the Wien oscillator which students have as part of their home experiment kit. In this circuit, the amplifier can be turned into an oscillator using feedback. The swept frequency technique is used to measure loop gain of the amplifier system. Animated diagrams and oscilloscope displays help to illustrate points made. Gaby Smol very briefly summarises the programme. |
| Master spool number: | OU 3516 |
| Production number: | FOUT074H |
| Videofinder number: | 2649 |
| Available to public: | no |
