SBAA491A November   2021  – April 2022 PCM5120-Q1 , PCM6120-Q1 , TLV320ADC5120 , TLV320ADC6120

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 Dynamic Range Enhancer
  4. 3 Dynamic Range Compressor
  5. 4 PGA Anti-Saturation
  6. 5 High Pass Filter
  7. 6 DRE/DRC Parameters
  8. 7 Sample Rate Support
  9. 8 Example
  10. 9 References
  11. 10Revision History

5 High Pass Filter

To remove any DC offset that leads to incorrect input level estimates, the DRE/DRC algorithm processes the input signal through a high-pass filter (HPF). This HPF is exclusive to the DRE/DRC and is different from the second-order HPF filters used by the decimation filters.

The transfer function implemented by the HPF is given by Equation 1.

Equation 1. GUID-53CFC256-6C2B-4651-90C6-CF858972A018-low.gif

The HPF is a first order filter implemented using three coefficients: DRE_HPF_B0, DRE_HPF_B1, and DRE_HPF_A1. The transfer function parameters (N0, N1, and D1) are converted to coefficients using Equation 2, Equation 3, and Equation 4.

Equation 2. DRE_HPF_BO = round(28 * N0)
Equation 3. DRE_HPF_B1 = round(28 * N1)
Equation 4. DRE_HPF_A1 = round(28 * D1)

These coefficients are user-programmable to set a different cutoff frequency from the default cutoff (3 dB point) frequency of 10 Hz for a 48 kHz operation. Increasing the cutoff frequency results in faster settling of signal-level estimates. Decreasing the cutoff frequency improves the accuracy of the signal-level estimate. The default filter coefficients provide a good balance between speed and accuracy and are suitable for most applications. Table 5-1 shows the coefficient registers of the HPF. The coefficients are represented in 2s-complement, 32-bit format.

Table 5-1 Programmable Registers for High Pass Filter Coefficients
COEFFICIENTPAGEREGISTERRESET VALUEDESCRIPTION
DRE_HPF_B00x060x6C0x7FDRE_HPF_B0 Byte[31:24]
0x060x6D0xFFDRE_HPF_B0 Byte[23:16]
0x060x6E0xFFDRE_HPF_B0 Byte[15:8]
0x060x6F0xFFDRE_HPF_B0 Byte[7:0]
DRE_HPF_B10x060x700x80DRE_HPF_B1 Byte[31:24]
0x060x710x00DRE_HPF_B1 Byte[23:16]
0x060x720x00DRE_HPF_B1 Byte[15:8]
0x060x730x01DRE_HPF_B1 Byte[7:0]
DRE_HPF_A10x060x740x7EDRE_HPF_A1 Byte[31:24]
0x060x750xEEDRE_HPF_A1 Byte[23:16]
0x060x760xD8DRE_HPF_A1 Byte[15:8]
0x060x770xE2DRE_HPF_A1 Byte[7:0]