cascode current source

The performance of the normal current source using a common- emitter connected transistor can be improved by the addition of just one more transistor. This is shown in the circuit diagrams. The influence of the TI collector voltage on the source current is greatly reduced through the action of T2. For mono reception of local FM transmitters with an indoor aerial, a very simple front-end is adequate. The input stage (TI) is operated in grounded base; band-pass filters are added at in- and output to reduce the level of transmitters outside the FM band. It would be possible, of course, to use a much sharper tuned circuit at the collector of T l. This would improve the selectivity and the sensitivity, but for a simple receiver such as this it is just not worth the extra expense.