[volt-nuts] 32-Bit PWM divider

[Andreas Jahn]

> Not really you should fit a straight line to the results first.
> The INL is then the given by the largest deviation from this straight 
> line.
>
As Randy already noted I measure the "end point INL".
I find this more useful when calibrating the endpoints and
then compensating the INL error by some kind of error curve.
In my case the error curve will be calibrated not so frequently as
the end points.
The best fit INL would give in most cases only about half the
value of the end point INL. So the datasheet values look
better if the best fit INL is used.

> A very clean board with low leakage from the supplies to the opamp inputs 
> together with shielding from air currents are necessary for low noise.
In my case the largest noise source is from the LTC2400 ADC which
is my best measurement equipment. He has 0.3ppm = 1.5uV
rms noise which will give about 10uVpp noise. Measurement condition
in the datasheet is with 0V at the input. The LT1027 reference of the ADC
contributes about 3uVpp. So practically I have about 8-20uVpp noise
over the full 0..5V input range. The only way to get rid of this noise is
to average many values.

> Did you make these measurements with the opamp powered up or with V+, V- 
> open, or even V+ and V- shorted together?
Good point: the opamp was not powered up so I have to check wether
I have measured the substrate diodes.

With best regards

Andreas