[sdiy] Testing OTA performance

[Magnus Danielson]

From: Paul Brown <gtg868h at mail.gatech.edu>
Subject: [sdiy] Testing OTA performance
Date: Thu, 4 May 2006 09:35:27 -0400
Message-ID: <4EFA744B-AC64-4F65-A1B9-B7EE740BF977 at mail.gatech.edu>

> Hey SDIYers,
> 	I am testing some parameters for various OTA's.  The OTA's being  
> tested are the 3080, LM13700, JRC13700, and JRC13600.  I have  
> measured the control current versus gain, and I also want to measure  
> the noise output of the OTA's.  I am thinking about hooking a large  
> amplifier up to the output of the OTA, with no input into the OTA,  
> and seeing how flat that output signal is.

"no input" as in grounded inputs or as in free-floating inputs?
I hope you meant grounded.

>  Are there any better  
> ideas out there?  Also, any ideas on how to measure the distortion of  
> these OTA's?

There are three parameters that comes to mind:
1) Input amplitude
2) Iabc current
3) Frequency

Also note that the input diodes and their use, as well as the source impedance
can certainly be another factor to look at for the distorsion.

I would pick three points of amplitude, Iabc and frequency respectively, giving
some 27 measurements. Then judging from that data I would increase the
resolution and area of interest on respecpective scale for what should be
expected normal mode of operation. Frequency is probably the only scale which
we already have a clue (I would look at 100 Hz, 1 kHz and 10 kHz to start
with).

Don't forget the moon-phase and time to next equinoxe!

Cheers,
Magnus