Subject: Re: VrefMain
From: Bill Forrest <[email-masked]>
To: Christoph Birk <[email-masked]>
Cc: Judy Pipher <[email-masked]>, Bill Forrest <[email-masked]>, Craig McMurtry <[email-masked]>, Rob Simcoe <[email-masked]>
Date: Fri, 07 Aug 2009 11:16:00 -0400

Hi Christoph,

We have been using the new HxRG_main?.mcd we got from Michael at Teledyne, along
with the Teledyne IDL code used to operate the array and ASIC.  Some of our data
is given Here:
http://astro.pas.rochester.edu/~forrest/SidecarASIC/

In talking to Michael, in order to use the differential input mode to the
preamp, one needs 2 reference voltages.  VrefMain balances the array output
(InPadP) and Vref1 balances the reference (InPCommon).  Following his suggestion
we first adjusted them to give near a zero output, this established that the
voltage of InPadP was near 1.6 V, and the voltage on InPCommon was near 1.8 V.

We set Vrefmain to 1.5 V and Vref1 to 1.75 V, to avoid the voltage floor of zero
volts, then adjusted Vrefmain to give a single frame level near 32,000 ADU (the
mid range of the A/D converter).  With these settings, we were able to go up to
the very maximum gain of 22.6, and got a read noise as low as 14 e- in one of
the four outputs.

We also found the 32 output mode was noisier than the 4 output mode, so we
concentrated on the 4 output mode for our FIRE spectrometer.

We also found, in 32 output mode, the noise was lower on the first, 3rd, 5th,
... outputs than the 2nd, 4th, ... outputs.  This effect was more pronounced
with the CryoSetup.mcd and StarServer than with the new HxRG....mcd and the IDL
program.

Bill

> On Tue, 28 Jul 2009, [email-masked] wrote:
>> That is because we stopped increasing the preamp gain - higher gains led
>> to topped out values.
> 
> Just to make sure we are not on a wild goose chase:
> Do we have an understanding that increasing the gain _should_
> increase the data numbers, correct?
> 
>>> What was the order of actions when you took these frames?
>>> Did you use the Menu->ASIC->VrefMain _after_ you uploaded
>>> the .mcd file?
> 
> Maybe VrefMain has no effect on the bare MUX. Did you
> ask TIS about that?
> 
> Christoph
>