[time-nuts] 10Mhz Sine from Square Wave Synthesizer

johncroos at aol.com johncroos at aol.com
Mon May 20 16:16:50 EDT 2013

Andy -

Glad to be of some small help. A couple of remarks re your comments 

John, thanks for your input, you reminded me that LFP performance often
depends on source impedance. To the MMIC amplifier, you'd be amazed what
you can do with an opamp these days. I was amazed reading the datasheet for
the LTC6409 a 10GHz GBW, 1.1nV/sqrt(hz) fully differential opamp. With a
gain of one, the frequency response is totally flat out to 1GHz.

 No actually I would not. I suggested the RF MMIC like one of the Mini-Circuits types because they have enough gain to recover the insertion loss of the input pad and the filter. They are also stable as a house not located in California. 

That leaves some gain margin for you to pad the output down to the desired level or to split it. As for the super duper chips methinks it is best to use no more performance capability than you need. Other wise you end up fighting oscillations, termination issues, and the necessity for very specific layout techniques. The hottest device is not always easiest to apply.

Actually a 2N2222 in common emitter will give more than 20 dB of gain and 100 mW out at 10 MHz and no microwave stability issues. It is just a matter of what is easiest for you to design and implement. 

-73 john k6iql



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