I need to acquire eight 0-5V analog signals using a 14bit multichannel PulSAR ADC, like the AD7949.
The bandwith of each analog signal is some kHz and I use a 2-nd order sallen-key low pass filter to provide both filtering and buffering function. The sallen-key cell is based on the ADA4610-2, whose features seems suggest that it could be a good choice as ADC buffer for this application. The filter is followed to a passive RC filter in order to attenuate the opamp residual noise.
In order to protect the opamp from the overvoltage event I use a series resistor and a clamping diode as depicted below.
- Since the series resistor R1 contributes to vary the corner frequency of the sallen-key cell, could it be recommended to use directly R2 as limiting resistor and place the clamping diode between R2 and R3 ?
If the opamp is powered at a voltage higher than the ADC, say +/-15V and supposing that the maximum current deliverable from the opamp (79mA in this case) is below the maximum current that the ADC can tolerate (130mA ), could I avoid to use overvoltage protection on the ADC input ?
- If I use resistor a clamping diode to protect the ADC input, what value of resistance could be reasonably used without affecting the ADC performance?
- Is it preferrable to use a filter followed to a buffer stage ?
Thanks in advance