SBAA401A July   2019  – January 2024 TLV320ADC3140 , TLV320ADC5140 , TLV320ADC6140

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Automatic Gain Control
    1. 2.1 High Pass Filter
    2. 2.2 AGC Parameters
  6. 3Examples
  7. 4References
  8. 5Revision History

2.1 High Pass Filter

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

The transfer function implemented by the high-pass filter 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: AGC_HPF_B0, AGC_HPF_B1, and AGC_HPF_A1. The transfer function parameters (N0, N1, and D1) are converted to coefficients using Equation 2, Equation 3, and Equation 4.

Equation 2. GUID-A2061A58-3A79-43A1-90E3-8B6F3962F0AF-low.gif
Equation 3. GUID-C0072E36-4174-4ABF-8A87-8DA0163929C7-low.gif
Equation 4. GUID-2D34EA92-786D-47AF-A466-27D9677E98E9-low.gif

These coefficients are user-programmable to set a different cutoff frequency from the default cutoff (-3 dB) of 100 Hz for a 48 kHz sample rate. Increasing the cutoff frequency results in faster settling of signal-level estimates, while 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. The coefficients are represented in 2s-complement, 32-bit format.

Table 2-2 Programmable Coefficient Registers for High Pass Filter
COEFFICIENT PAGE REGISTER RESET VALUE DESCRIPTION
AGC_HPF_B00x060x780x7FAGC_HPF_B0 Byte[31:24]
0x060x790x7FAGC_HPF_B0 Byte[23:16]
0x060x7A0xD2AGC_HPF_B0 Byte[15:8]
0x060x7B0xB4AGC_HPF_B0 Byte[7:0]
AGC_HPF_B10x060x7C0x80AGC_HPF_B1 Byte[31:24]
0x060x7D0x80AGC_HPF_B1 Byte[23:16]
0x060x7E0x2DAGC_HPF_B1 Byte[15:8]
0x060x7F0x4CAGC_HPF_B1 Byte[7:0]
AGC_HPF_A10x070x080x7EAGC_HPF_A1 Byte[31:24]
0x070x090xFFAGC_HPF_A1 Byte[23:16]
0x070x0A0xA5AGC_HPF_A1 Byte[15:8]
0x070x0B0x68AGC_HPF_A1 Byte[7:0]