AD977A: is it possible to use one AD780 to be the ref voltage of 16 AD977A for +-10V range?

Q Is it possible to use one AD780 to be the ref voltage of 16 AD977A for +-10V range? A It will cause problems. For AD977A, there is a current from AD780 to R3IN (See circuit in fig 16a/16b, attached). Therefore AD977A will interfere others. You should use AD8031/2 as the buffer in front of each AD977A. Or you can use AD977 since the connection is different. Attachments:

AD977A: Driving the inputs

Q For our project, our pcb design is completed by using ad977a. After that point we started pcb tests. We observed problems for digitization process. We are trying to digitize the analog signal which is +/-10 v and 1k ohm output impedance. Can you please say that 1k ohm output impedance is a problem. A The AD977A uses an on-chip resistive divider to scale and shift the +/-10V input range so that it fits the 0 to 2.5V range of the ADC. This resistive scaling circuitry has a realtively low input impedance, table 1 on page 14 of the AD977A datasheet shows that the AD977A input impedance is 11.5kOhms for the +/-10V input range. This must be driven from a very low impedance source if errors at the 16-bit level are to be avoided. In practise the best way to achieve a very low source impedance is to buffer the input. We have an op amp whch is especially suitable for buffering the input to a 16-bit ADC, the AD8021. The datasheet for the AD7663 shows how to use the AD8021.