life speed wrote:
Hello everyone,
I am new to this list, happened across it while searching on distribution
amplifiers.
I need to design a 10 MHz isolation/distribution amplifier with two outputs for
a high-vibration wide temperature range environment. I was considering using a
design based on the NIST article 'A new 5 and 10 MHz distribution amp', most
likely the third incarnation, as I cannot tolerate modulation of the signal via
the transformer.
I have looked at the work by Gerhard Hoffman, which is impressive. However,
the transformer remains. I should mention I am also limited to 15V power
supply, and need to output into 50 ohms at 10 dBm. Ideally DC current will be
minimized, preferably 20 - 30 mA per channel. I can generate a negative power
supply if necessary, but would prefer not to.
If anybody can offer tips so I don't undertake to reinvent the wheel, it would
be appreciated.
Thanks in advance,
- Lifespeed
Avoiding transformers and inductors will make it virtually impossible to
achieve very low phase noise as the dc gain from say the base of any
transistor in the chain to the output will degrade the flicker phase
noise. Using transformers or using an inductor to shunt any collector
resistors reduces the flicker phase modulation to low levels.
JPL in the past has built capacitively coupled complementary symmetry
isolation amplifiers that avoid transformers but suffer from dc loop
gains of around 3 or so.
Using complementary symmetry can be a good way of keeping the dc current
down.
How much reverse isolation do you need?
How low does the phase noise floor need to be?
What about flicker phase noise, how low does that need to be?
Bruce
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