ES9218PC datasheet(16/101 Pages) ESS

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ES9218P Datasheet

December 6, 2018

CONFIDENTIAL ADVANCE INFORMATION 1.8

ESS TECHNOLOGY, INC. 237 South Hillview Drive, Milpitas, CA 95035, USA Tel (408) 643-8800 • Fax (408) 643-8801

Programmable FIR filter

A two stage interpolating FIR design is used. The interpolating FIR filter is generated using MATLAB, and can then be downloaded using a custom

C code.

Example Source Code for Loading a Filter

// only accept 128 or 16 coefficients

// Note:

The coefficients must be quantized to 24 bits for this method!

// Note:

Stage 1 consists of 128 values (0-127 being the coefficients)

// Note:

Stage 2 consists of 16 values (0-13 being the coefficients, 14-15 are zeros)

// Note:

Stage 2 is symmetric about coefficient 13.

See the example filters for more information.

byte reg40 = (byte)(coeffs.Count == 128 ? 0 : 128);

for (int i = 0; i < coeffs.Count; i++)

{

// stage 1 contains 128 coefficients, while stage 2 contains 16 coefficients

registers.WriteRegister(40, (byte)(reg26 + i));

// write the coefficient data

registers.WriteRegister(41, (byte)(coeffs[i] & 0xff));

registers.WriteRegister(42, (byte)((coeffs[i] >> 8) & 0xff));

registers.WriteRegister(43, (byte)((coeffs[i] >> 16) & 0xff));

registers.WriteRegister(44, 0x02);

// set the write enable bit

}

// disable the write enable bit when we’re done

registers.WriteRegister(44, (byte)(setEvenBit ? 0x04 : 0x00));

For more information on programming a custom filter, contact your local FAE.

OSF Bypass

The oversampling FIR filter can be bypassed using bypass_osf in Register 7: Filter Bandwidth and System Mute (0x07), sourcing data directly

into the IIR filter. The audio input should be oversampled at 8 x fs rate when OSF is bypassed to have the same IIR filter bandwidth as PCM

audio sampled at fs rate. 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 or LJ format. The maximum sample rate that can be applied is 768kHz (8 x 96kHz).

DSD Filter

A DSD filter with cutoff at 47kHz scaled by fs/44100 is available. See DSD FILTER Characteristics for more information.

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