[time-nuts] new op amp for distribution amplifiers

[Anders Wallin]

Stylish dead-bug! ;)
On my board I increased Rf/Rg to 4k7, to get rid of the gain-peaking.
With 4k7 resistors I see +20 dBc/Hz worse phase-noise with the THS3491
compared to LMH6702 :(  (image attached)
If noise power scales with the resistors then it explains about 4k7/200R =
14 dB, for one amp, and perhaps 17 dB for two amps. Still missing 3dB
somewhere in that reasoning...

John: would you say if one can use the suggested 976R Rf/Rg resistors then
below -160dBc/Hz for a 10MHz carrier is possible for a gain of +2?

At least we can say THS3491 is much more tricky to work with than LMH6702
so far... (?)

Anders
[image: ths2.png]

On Mon, Dec 17, 2018 at 9:04 AM John Miles <john at miles.io> wrote:

> > -----Original Message-----
> > From: time-nuts [mailto:time-nuts-bounces at lists.febo.com] On Behalf Of
> > Anders Wallin
> > Sent: Saturday, December 15, 2018 9:03 AM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] new op amp for distribution amplifiers
> >
> > Hello Gerhard, everyone,
> >
> > I made a test using the THS3491 on a slightly modified PCB from my "FDA"
> > design [1]...
>
> A few more notes on the THS3491:
>
> http://www.ke5fx.com/ths3491.htm
>
> I had tested it a few weeks ago, but hadn't gotten around to gathering and
> sorting through the plots.
>
> -- john, KE5FX
> Miles Design LLC
>
>
>
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