Analog Input Configurations, Mixing and Muxing of TAx5x1x Devices

Abstract

The TAx5x1x (TAC5212, TAC5211, TAC5112, TAC5111, TAA5212, TAC5242, TAA5242, TAC5142) family of devices have single or dual-channel analog-to-digital converters which supports highly configurable inputs for audio applications. This application note looks at the different input configurations such as input swing, common mode setting, AC/DC Coupling in normal and low power mode as well as the mixing and muxing option that are supported in this TAx5x1x device family. TAC5212, a stereo software control device is used in this application note as an example. For hardware pin control, the pin configurations for the input are provided in the respective data sheet. The audio input in this note is provided from LINE input. Microphone inputs or a mono version of this device can be configured in the similar manner.

Trademarks

All trademarks are the property of their respective owners.

1 Introduction

TAC5212 is a CODEC with dual-channel analog-to-digital converters whose input pins (IN1P/M and IN2P/M) are configurable as differential inputs, single-ended inputs or single-ended mux inputs in AC or DC coupling. The type of input is configured through ADC_CH1_INSRC, the input impedance is configured through ADC_CH1_IMP and the coupling and common-mode tolerance is configured through ADC_CH1_CM_TOL.

Table 1-1 Input Configuration Selection

Input Configuration Setting	B0_P0_R80 (ADC_CH1_CFG0) [7:6]	Input Channel Configuration
0	ADC_CH1_INSRC=[00]	Analog differential input
1	ADC_CH1_INSRC=[01]	Analog single-ended input
2	ADC_CH1_INSRC=[10]	Analog single-ended mux INP1 input
3	ADC_CH1_INSRC=[11]	Analog single-ended mux INM1 input

Table 1-2 ADC Input Impedance Selection

Input Impedance Setting	B0_P0_R80 (ADC_CH1_CFG0) [5:4]	ADC Channel 1 Input Impedance
0	ADC_CH1_IMP=[00]	Typical 5-kΩ input impedance (For 4 Vrms case, is 10-kΩ)
1	ADC_CH1_IMP=[01]	Typical 10-kΩ input impedance
2	ADC_CH1_IMP=[10]	Typical 40-kΩ input impedance
3	ADC_CH1_IMP=[11]	Reserved

The common-mode tolerance is defined as the variation of the common mode signal of the differential amplifier, this is depicted in Figure 1-1.

Figure 1-1 Common-Mode Tolerance

In AC-Coupling mode, this device family supports three common mode tolerances; differentially 100 mVpp, 1 Vpp and rail-to-rail (supply to ground) and in DC-Coupling mode, it supports differentially of 1 Vpp and rail-to-rail (supply to ground). This common mode tolerance needs to be selected based on the maximum expected common-mode variation. Since wider common-mode tolerance does degrade other performance parameters, the recommendation is to select the lowest tolerance mode possible.

Table 1-3 Common-Mode Tolerance Selection

Common-Mode Tolerance Setting	B0_P0_R80 (ADC_CH1_CFG0) [3:2]	Input Channel Common-Mode Tolerance
0	ADC_CH1_CM_TOL=[00]	AC-coupled input with common mode variance tolerance supported 50 mVpp for single ended and 100 mVpp for differential configuration
1	ADC_CH1_CM_TOL=[01]	AC-coupled / DC-coupled input with common mode variance tolerance supported 500 mVpp for single ended and 1 Vpp for differential configuration (Expected SNR degradation of 1-2 dB)
2	ADC_CH1_CM_TOL=[10]	AC-coupled / DC-coupled input with common mode variance tolerance supported rail to rail (supply to ground) (Expected SNR degradation of approximately 35 dB, High CMRR supported only in this case)
3	ADC_CH1_CM_TOL=[11]	Reserved

Note that it is important to keep in mind the full-scale range (Vswing) of the device in all modes. This is especially important for large common-mode signals as they will limit the effective input range. In Mode 1 DC-Couple for example, a 500 mVp common voltage variant from the device internal common mode voltage of 1.375 V will limit the Vswing to 3.75 Vpp single-ended or 7.5 Vpp (2.65 Vrms) differential. In mode 2, it can support a common-mode range of 0V to Supply, but there would be no room left for a differential signal to be applied to the input pins at either of these extremes.

Figure 1-2 Mode 1 Common-Mode Example

Figure 1-3 Mode 2 Common-Mode Example

2 Analog Input Configuration

Table 2-1 provides a summary of the different input configurations for IN1 in this application note, the same applies to IN2 input with the register channel change to 2.

Table 2-1 IN1 Input Configuration and Input Swing

Input Pin	Input Mode	Input Swing
IN1P-IN1M	LINE-IN Differential, AC-coupled	2 Vrms
IN1P	LINE-IN Single-Ended, AC-coupled	1 Vrms
IN1P	LINE-IN Single-Ended Mux IN1P, AC-coupled	1 Vrms
IN1M	LINE-IN Single-Ended Mux IN1M, AC-coupled	1 Vrms
IN1P-IN1M	LINE-IN Differential, DC-coupled	4 Vrms
IN1P	LINE-IN Single-ended, DC-coupled	2 Vrms
IN1P	LINE-IN Single-ended Mux IN1P, DC-coupled	2 Vrms
IN1M	LINE-IN Single-ended Mux IN1M, DC-coupled	2 Vrms

For each of the test, audio signal is provided from APx500 analog balance or unbalanced output with input level referenced to the full-scale swing of the device configuration for example 0 dBrG is referenced to 2 Vrms single ended swing or 4 Vrms differential input swing in DC-Coupled configuration.