SBAA400A September   2019  – December 2023 PCM5140-Q1 , PCM6140-Q1 , TLV320ADC5140 , TLV320ADC6140

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Dynamic Range Enhancer
    1. 2.1 High Pass Filter
    2. 2.2 DRE Parameters
    3. 2.3 Sample Rate Support
  6. 3Example
  7. 4References
  8. 5Revision History

2.1 High Pass Filter

To remove any DC offset that leads to incorrect input level estimates, the DRE algorithm processes the input signal through a high-pass filter (HPF). This HPF is exclusive to the DRE 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-CFE9125F-B2A2-4019-8B8B-E0156951ABA1-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_B0=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 2-2 shows the coefficient registers of the HPF. The coefficients are represented in 2s-complement, 32-bit format.

Table 2-2 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]