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ES9018S Product Datasheet

FIR Programmable Filters

The SABRE32 Reference has a two-stage interpolating filter with both built-in and programmable coefficients. Each stage can be programmed and

enabled independently. Each channel can also have a different filter per stage.

Each stage of the FIR filter either uses the built-in coefficients, or the programmable coefficients. Register 37 bits 5 and 1 are used for setting the

filter coefficient sources.

Programming the filter requires passing every coefficient for all 8 channels to the SABRE32 Reference via I2C. Stage 1 and Stage 2 must be

programmed independently. Programming starts by enabling the appropriate enable_programming bit in register 37.

The FIR can only be programmed when DATA_CLK is available and when the DAC is locked.

To program stage 1, bit 4 of register 37 must be set high. Then the 32bit coefficients are written to registers 41 (Bits [31:24]), 40 (Bits[23:16]), 39

(Bits[15:8]), 38 (Bits[7:0]) in that order. The first write to these 4 consecutive register is the 32-bit value for Channel1, coefficient1. The next write to

these 4 consecutive registers is the 32-bit value for Channel2, coefficient1. After 8 writes to these 4 consecutive registers, coefficient 2 for all 8 filters

is ready to be input. There are 64 coefficients to write for Stage 1. So that is 4 bytes per coefficient, 8 channels and 64 coefficients for a total of

2048 bytes to program the stage 1. Once complete, zero must be written to register 38. Bit 4 of register 37 must then be set low to finalize the

programming.

To program stage 2, bit 0 of register 37 must be set high. Then the 32bit coefficients are written to registers 45 (Bits [31:24]), 44 (Bits [23:16]), 43

(Bits [15:8]), 42 (Bits [7:0]), in that order. The first write to these 4 consecutive register is the 32-bit value for Channel1, coefficient1. The next write

to these 4 consecutive registers is the 32-bit value for Channel2, coefficient1. After 8 writes to these 4 consecutive registers, coefficient 2 for all 8

filters is ready to be input. There are 16 coefficients to write for Stage 2. So that is 4 bytes per coefficient, 8 channels and 16 coefficients for a total

of 512 bytes to program the stage 1. Once complete, zero must be written to register 42. Bit 0 of register 37 must then be set low to finalize the

programming.