Okay, I think I made some improvements from the last few schematics I posted. The major difference is that the driver stage works in class A mode, which minimises the need for filtering between stages, and also increases the maximum output power, because less power is spent in transmitting harmonics, which are either way suppressed by the filter, and more power is spent on the fundamental. The other major advantage is that for a power output of 7.7W the input power is only 20mW. This means you can hook a simple cheap car FM transmitter to this amp and still make a pretty professional FM transmitter. One more advantage is the somewhat improved efficiency of the output stage. This is mainly due to the fact that the power amplifier spurs out a very clean signal, which needs minimal filtering and transfers almost the maximum power to the antenna. This improves the Vout/Vcc ratio and thus the efficiency. The amp seems pretty stable, no self-modulating is observable.
P.S. If you ask me you can probably get by, with a single Pi-Filter, cause the output is clean either eat, but the more filtering the better. This way there are virtually no harmonic emmisions from the amp.
Some of the specs are:
- Input Power - 20mW
- The drawn power for the driver stage is 2.4W
- The drawn power of the Output Stage is 10.8W
- The Output Power is 7.7W
- The overall harmonic suppresion is -57dB, and can actually be higher I don't know if I measured it reliably
