Whilst out walking and pondering, as one does....
There are hundreds of designs out there for linear power amps using FETS. They all use a similar design, push-pull with centre tapped ferrite cored transformers at input and output, often with resistive feedback - and all broadband. The design is so
standard it's become tedious ... and as I don't do tedious, it made me think:
Back in days of yore when those big bottles ruled the roost , apart from a few designs for UHF, they were all single ended.
So, why not a single ended MOSFET amp (for single band operation)? We're used to seeing single device for class-E, where the tank circuit does much of the waveform cleaning, and reduces the low pass filter requirements. So what's wrong with a tank-based
design for class-B?
A single ended amp can even be made ferrite free (although a final stage DC feed choke would no doubt benefit from it). Apart from a few very low power designs, I don't recall seeing any designs for single band ferrite free linear amps using power MOSFETS.
Only major downsides I visualise is that load resistance at the device is 4 times lower for the same Vdd and Pout , and device dissipation is doubled
Has no one ever bothered, because broadband transformer push-pull is so straightforward?
Has a trick been missed?
Andy G4JNT
