[time-nuts] dual supplies Re: Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Lux, Jim]

On 7/10/22 9:07 AM, Bob kb8tq via time-nuts wrote:
> Hi
>
> Yes it is a pain to implement dual supplies. I ponder that issue every time
> I build one of these setups. I’ve built a lot of them …. If you are going to
> do a single supply, setting up a “virtual ground” is probably the best way
> to go. Do it with a drive circuit to provide very clean 15V off of a 30V supply
> then tack everything ( including *all* the mixer grounds to that 15V supply.


Yeah, but that virtual ground brings with it it's own set of problems. 
For instance, it has to both sink and source current, so you can't just 
use a 3 terminal regulator to create the midpoint, although I've seen 
schemes with a resistor from virtual ground to negative supply, but 
that's not very power efficient - the resistor needs to see, say, 10x 
the maximum sink current.

Now that I think about it, some sort of op amp driven appropriately (or 
a complementary PNP/NPN pair?) might work - but then you're concerned 
about the output Z of the op amp, and how it varies over frequency. And, 
of course, the bias current.

We face this in designing low noise instruments for space. You're 
running off a DC bus of some sort, and DC/DC inverters tend to be 
noisier than straight out buck converters or linear regulators.