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i have four FIR filters and i want to control the gain in the output of each filter and then sum their outputs. The result is sended to an DAC.
it is possible to control the gain in fpga?
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There's a couple of solutions;
1) Add a gain block (multiplier) between each FIR filter output and the summing block.
2) If the FIR filter coefficients are re-loadable, then use the coefficients to implement the gain function, by scaling them appropriately.
The second option requires a little care regarding the dynamic range of the signals. However, depending on the bit-widths of your signal and coefficients, the scaling may be available 'for free', eg. lets say you have a design with 16-bit data and coefficients, and the design is using hardware multiplers, because the multipliers are 18x18-bit, you have a couple of extra bits that you can use for the gain function. If that is sufficient, then you get your gain function for free.
Cheers,
Dave
Honored Contributor
