Sean:

Yes, if cost is important factor alone you would want to set the noise
figure or performance of the system by the first stage. To do that the
first stage power gain must be 3dB or more. So if you've put you money
into a good front-end amp, get as much gain-bandwidth as you can. Get it
while the signal swing is small so the non-linear effects of the
"linear" amps are minimal.

However, since as you point out, other stages contribute noise and
spurious signals if you are forced to use distributed gain (limited by
stage gain-bandwidth, for example). The amplifier second order
characteristics (PSRR, CMRR, THD, etc.), physical layout and supply
bypassing become more important for following stages. So total costs
will go up.

- Wayne Foletta
BMI - Santa Clara

> ----------
> From:         Sean Breheny[SMTP:shb7@CORNELL.EDU]
> Sent:         Thursday, November 20, 1997 3:54 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: Serial Sonar Unit (SSU)
>
> >>4. Use lowest noise preamp possible with gain of 10x to set noise
> floor
> >>of system. (You [can] use a lower first stage gain but that puts
> lower noise
> >>requirements on the following stages.)
>
> Don't you want as much gain in this first amp stage as possible? Each
> amp
> in the chain creates noise, so you want to amplify it as little as
> possible, so concentrating your gain in the first stage would be best,
> wouldn't it?
>
> Sean
>
>
> +--------------------------------+
> | Sean Breheny                   |
> | Amateur Radio Callsign: KA3YXM |
> | Electrical Engineering Student |
> +--------------------------------+
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