The device consists of two pairs of analog input pins (INxP and INxM) that can be configured as differential inputs or single-ended inputs for the recording channel. The device supports simultaneous recording of up to two channels using the high-performance multichannel ADC. The input source for the analog pins can be from electret condenser analog microphones, microelectrical-mechanical system (MEMS) analog microphones, or line-in (auxiliary) inputs from the system board. Analog inputs support differential input, single-ended inputs(two pin and one-pin) with AC and DC coupling options. Additionally, if the application uses digital PDM microphones for the recording, GPIO,GPI and GPO pins can be reconfigured in the device to support up to four channels for the digital microphone recording. TAA5212 supports incremental mode of ADC where analog input channels can be used for DC measurements. This can be configured by setting IADC_EN(P0_R81_D7). Table 8-8 shows the input source selection for the record channel.

Similarly, the input source selection setting for input channel 2 can be configured using the ADC_CH2_INSRC[1:0] (P0_R85_D[7:6]) register bits.

Typically, voice or audio signal inputs are capacitively coupled (AC-coupled) to the device; however, the device also supports an option for DC-coupled inputs to save board space. This configuration can be done independently for each channel by setting the input common mode tolerance in ADC_CH1_CM_TOL (P0_R60_D[3:2]), ADC_CH2_CM_TOL(P0_R85_D[3:2]) register bits. The INM pin can be directly grounded in Rail to Rail Common Mode (see Figure 8-15), but the INM pin must be grounded after the AC-coupling capacitor whenever ADC_CHx_INSRC is set to 2'b01 and ADC_CHx_CM_TOL is set to 2'b01(see Figure 8-16) for the single-ended input configuration. For the best dynamic range performance, the differential AC-coupled input must be used .

Figure 8-15 Single-Ended DC-Coupled Input Connection

Figure 8-16 Single-Ended AC-Coupled Input Connection

The device allows for flexibility in choosing the typical input impedance on INxP or INxM from 5 kΩ (default), 10 kΩ, and 40 kΩ based on the input source impedance. The higher input impedance results in slightly higher noise or lower dynamic range. Table 8-9 lists the configuration register settings for the input impedance for the record channel.

Similarly, the input impedance selection setting for input channel 2 can be configured using the ADC_CH2_IMP[1:0] (P0_R85_D[5:4]).

The value of the coupling capacitor in AC-coupled mode must be chosen so that the high-pass filter formed by the coupling capacitor and the input impedance do not affect the signal content. Before proper recording can begin, this coupling capacitor must be charged up to the common-mode voltage at power-up. To enable quick charging, the device has modes to speed up the charging of the coupling capacitor. The default value of the quick-charge timing is set for a coupling capacitor up to 1 µF. However, if a higher-value capacitor is used in the system, then the quick-charging timing can be increased by using the INCAP_QCHG (P0_R5_D[7:6]) register bits. For best distortion performance, use the low-voltage coefficient capacitors for AC coupling.