ES9039Q2M datasheet(33/107 Pages) ESS

33 / 107 page

VERSION 0.2.2

ESS TECHNOLOGY, INC. 109 Bonaventura Drive, San Jose, CA 95134, USA Tel (408) 643-8800 • WWW.ESSTECH.COM

ES9039Q2M Product Datasheet

Customizable Programmable FIR Filters

The ES9039Q2M has an 8x interpolation oversampling FIT filter that is programmable. It is a combination of 2 filters, a 4x

FIR filter and a 2x FIR filter.

These filters can be bypassed using Register 90[1] BYPASS_FIR4X & 90[0] BYPASS_FIR2X, which will source data to the

IIR filter. It is recommended to use an 8xFS input if the bypass is used. For example, an external signal at 44.1kHz can be

oversampled externally to 8 x 44.1kHz = 352.8kHz and then applied to the serial decoder in either I²S, LJ or RJ format.

The addresses for the two filters are:

• 2x FIR, Address 0x00 - 0x7F (0 - 127), 128 coefficients

• 4x FIR, Address 0x80 - 0x9F (128 - 159), 32 coefficients

To program the filters, the following registers are required:

• Register 135: PROGRAM RAM CONTROL

[1] PROG_COEFF_WE

▪

Enables writing to the programable coefficient RAM

[0] PROG_COEFF_EN

▪

Use the built-in filters or custom filter

• Register 137: PROGRAM RAM ADDRESS

[7] PROG_COEFF_STAGE

▪

Choose which FIT stage to write to, either 4x or 2x

[6:0] PROG_COEFF_ADDR

▪

Selects the coefficient address when writing custom coefficients for the interpolation oversampling

filter

• Register 140-138: PROGRAM RAW DATA

24-bit signed filter coefficient to the address defined by PROG_COEFF_ADDR

• Register 248-246: PROG COEFF OUT READ

Used to readback the programmed coefficients

An example sequence of programming a coefficient into RAM:

Write Reg 137 0

// RAM Address = 0, 2x stage

Write Reg 138 32

// Set data bits [7:0] of 24 bit coefficient

Write Reg 139 255

// Set data bits [15:8]

Write Reg 140 255

// Set data bits [23:16]

Write Reg 135 0x02

// Write 24 bit coefficient to RAM

Write Reg 135 0x00

// Reset write enable

Repeat for all 4x and 2x coefficient addresses.

An application note the programming sequence and sample code is available from your ESS Distributor or FAE.

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