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    Negative voltage needed in K-band

    Hello,

    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

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    Re: Negative voltage needed in K-band

    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.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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    Re: Negative voltage needed in K-band

    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.


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  4. #4
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    Re: Negative voltage needed in K-band

    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.

    Click image for larger version. 

Name:	Neg 10v from 5v positive pulses 2-invert-gate oscill Dickson stages 3k load.png 
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    The 30 ohm resistors are not absolutely necessary. They reduce spikes. An inverter gate can be made from a half-bridge.


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