[time-nuts] Opamp Phase noise: OPA653 additional measurements

Azelio Boriani azelio.boriani at screen.it
Tue Apr 17 12:06:43 UTC 2012


OK, I'll follow the Enrico Rubiola/TSC5120 literature.

On Tue, Apr 17, 2012 at 1:39 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> My *guess* is that your 1Hz data may be as much from ambient changes as
> from the op amps themselves. No data to back that up on these specific
> parts, just a guess.
>
> Bob
>
> On Apr 17, 2012, at 7:28 AM, Bruce Griffiths wrote:
>
> > Not yet, I just used the pair of TI evaluation boards which I obtained
> for another project.
> >
> > I intend to mount the various components (splitters, 180 degree hybrids
> etc) on a thick aluminium plate to improve the mechanical and thermal
> stability of the system.
> >
> > Bruce
> >
> > Bob Camp wrote:
> >> Hi
> >>
> >> Did you do any temperature stabilization on the op amps?
> >>
> >> Bob
> >>
> >> On Apr 17, 2012, at 5:25 AM, Bruce Griffiths wrote:
> >>
> >>
> >>> Subsequent measurements using an improved technique has allowed the
> true flicker phase noise characteristics of  a pair of OPA653 opamps to be
> determined.
> >>>
> >>> Opamp
> >>>    Gain 1x (6db folled by 6 db attenuator consisting of a 50 ohm
> resistor in series with the output of the opamp and the 50 ohm load
> resistor)
> >>>    Signal input level: + 10dBm
> >>>
> >>> OFFSET    Opamp PN (dBc/Hz)    Measurement system PN (dBc/Hz)
> >>>
> >>> 1                -148                                -161
> >>>
> >>> 10              -161                                -172
> >>>
> >>> 100            -164                                -177
> >>>
> >>> 1000          -164                                -179
> >>>
> >>> Source: 10MHz low phase noise OCXO removed from a Thunderbolt
> amplified by a QBH9816 amplifier.
> >>>
> >>> Conclusion: FET opamp PN in the flicker region can be quite low
> despite its somewhat higher baseband flicker noise than that of some
> bipolar input opamps.
> >>>
> >>> Bruce
> >>>
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> >
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