Bruce Griffiths wrote: > Bill Hawkins wrote: > >> Bruce Griffiths wrote: >> >> >>> Poul-Henning Kamp wrote: >>> >>> >>>> In message <[email protected]>, Kasper Pedersen writes: >>>> >>>> >>>> >>>>> Bruce Griffiths wrote: >>>>> The charge redistribution adc would have been good, true, but there >>>>> wasn't one in my junkbox. >>>>> >>>>> >> If it wouldn't be too much trouble, could you change the Subject line? >> This is not about happy days at all. >> >> Bill Hawkins >> >> >> >> > To account for charge injection effects from the ADC multiplexer and the > residual voltage on the ADC sampling capacitor as well as the inevitable > gain mismatch between the 2 channels a more comprehensive model of the > TAC's + ADC will be required. To a first order approximation such > effects will be small and linear a model something like > > t2-t1 = G*(V2-V1) + e*V1 may suffice. > > Where > V2 is the voltage across the second TAC ramp cap as measured by the ADC > V1 is the voltage across the second TAC ramp cap as measured by the ADC > > > This equation will need to be elaborated slightly when the initial > voltages across the TAC capacitors (during reset) are also measured. > The exact form of the correction will depend on the order in which the > voltage measurements are made. > > Ideally the 2 synchroniser circuits would be include the capability of > producing calibration signals of known duration to facilitate > calibration of the gains of the 2 TACs whenever required. > > > Bruce > > Equation should have been
t2-t1 = G*(V2-V1) + e*V1 + offset. Where G is the TAC gain E is a small coefficient that accounts for TAC gain mismatch and the residual voltage on the ADC sampling cap. offset is a time offset principally due to propagation delay mismatch between the 2 synchronisers. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
