Negative voltage needed in K-band
I am trying to incorporate a medium power PA into my circuit, which had only positive voltages before that. For this PA, I need to include a negative gate voltage for active bias purposes. What sort of practical difficulties are there for getting a negative voltage signal into my circuit?
My frequency is K-Band ISM, and the voltage value needed is -6Volts. I use Rogers4350 10mil as my PCB.
Waiting for an answer hopefully.
Best Regards,
ktr
I assume as a gate voltage source, the current requirement is fairly low.
Use any negative voltage generator IC or use one of the many DC-DC inverter 'bricks' (NME1212 or similar) with the isolated output connected with positive output to ground.
Brian.
Active bias wants that negative voltage controlled,
to get a chosen drain current setpoint. The -6V is
probably the supply rail and pinchoff of the FETs /
HEMTs probably about -3V, to be set by a feedback
amplifier (or cal-mapped DAC, or ...).
I have no good idea of the amplifier particulars to
say whether the negative voltage pin is the supply
(with active bias amp on chip) or the control point
(bias gate network brought out, bare).
The problem with a close-in inverter switcher is that
it's going to throw switching noise onto the bias gate
network unless you are really careful with filtering.
Spurs at 100K - 1MHz offset will really mess up your
frequency mask compliance.
The gate network wants a low impedance to keep
noise down (forget which kind, but that's what the
microwave module guys I designed element control
chips for, told me).
If you use a voltage inverter DC-DC then you will
want to give it enough headroom to put a linear
regulator with good HF PSRR between it and the
amplifier, and filter before and after the linear
regulator.
Or, you insist that the customer provide the
Vg supply with such-and-such attributes, that
enables you to meet noise specs.
Method to derive a negative supply from positive pulses. The oscillator is made from 2 invert-gates (powered by a default 5V supply although of course you can use your 6v supply). The Dickson voltage multiplier has the diodes oriented to produce negative output. Output is ground referenced.
The 30 ohm resistors are not absolutely necessary. They reduce spikes. An inverter gate can be made from a half-bridge.