We have selected the programmable filter ADRF6510 from Analog Devices to be part of a new RF design.
There are two filters in our design, one for the Tx channel and the other one for the Rx channel.
The main performances we require from this component are:
- Signal filtering up to 20 MHz for the Tx channel.
- Signal filtering up to 30 MHz for the Rx channel.
- Differential inputs and outputs and I/Q signals
We were testing the filter by using its evaluation board before chosen it for our final design, and we have followed the schematics showed in the evaluation board to connect the filter properly in our design. The Rx channel filter is connected to the AD9640 from Analog Devices, and the Tx channel filter is connected to the DAC5687 from Texas Instruments.
Now we are testing the board where the filter is mounted and we have encountered some problems with this component. With our current setup, we can set the corner frequency properly since we perform write and read cycles successfully, but there are always the same signals present at the filters output even when there are no input signals present. These signals are periodic and don´t change when the inputs are present. The front end gain is set to 6dB and the continuous gain is set to -5dB.
After test many solutions, we think that the problems could be related to the common-modes for input and outputs or with the offset correction.
We would be very grateful if you could provide us with information about the cause of the problems.