D
Dave Boland
- Jan 1, 1970
- 0
All,
I have some questions that I hope some of you have dealt
with. The first is if it is wise to front-end a voltage
follower circuit with a resistor to gnd. when it is likely
that the Vin can be removed with the op amp still powered -
see below.
Vin >>----+------|Op Amp |--------|Rfilt|----+----|ADCin
| |V.Follow | |
Rb Cfilt
| |
Gnd Gnd
There is a connector in front of each analog input, so it is
likely some of the inputs will float. The problem I see is
that Rb will effectively be the input impedance, which is
not what I really wanted. Do I really need it and are there
any other concerns that I should be aware of?
The other question involves Cfilt. I want to use an R-pack
and a C-pack (C-array??) so that the R & C variance from one
ADC input to another is small (ADC inputs can be used
differentially). The problems are that I can't find any
capacitor arrays that are more than 4, and I want to use NPO
but can't find any in the 4000pF range. Individual caps can
be found, but I don't know what the variance between them
is. Suggestions?
Thanks,
Dave
I have some questions that I hope some of you have dealt
with. The first is if it is wise to front-end a voltage
follower circuit with a resistor to gnd. when it is likely
that the Vin can be removed with the op amp still powered -
see below.
Vin >>----+------|Op Amp |--------|Rfilt|----+----|ADCin
| |V.Follow | |
Rb Cfilt
| |
Gnd Gnd
There is a connector in front of each analog input, so it is
likely some of the inputs will float. The problem I see is
that Rb will effectively be the input impedance, which is
not what I really wanted. Do I really need it and are there
any other concerns that I should be aware of?
The other question involves Cfilt. I want to use an R-pack
and a C-pack (C-array??) so that the R & C variance from one
ADC input to another is small (ADC inputs can be used
differentially). The problems are that I can't find any
capacitor arrays that are more than 4, and I want to use NPO
but can't find any in the 4000pF range. Individual caps can
be found, but I don't know what the variance between them
is. Suggestions?
Thanks,
Dave