The TAA5212 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 channels. The device supports simultaneous recording of up to two analog 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 inputs and single-ended inputs with AC and DC coupling options.

Table 6-9 shows the input configuration for the record channel 1.

Similarly, the input configuration 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 and the common-mode variation at the device input is limited to less than 100mVpp for differential inputs. However, for applications that cannot avoid large common-mode fluctuations or when needed to save board space, the device also supports options for increasing the common mode tolerance and for DC-coupled inputs. This configuration can be done independently for each channel by setting the input common mode tolerance in ADC_CH1_CM_TOL (P0_R80_D[3:2]) and ADC_CH2_CM_TOL (P0_R85_D[3:2]) register bits. Table 6-9 shows these options for Channel 1. Setting higher common mode tolerance offers improved CMRR performance at the expense of noise performance by a few decibels.

See Figure 6-15 to Figure 6-18) for the various typical input configuration diagrams. For single-ended inputs, the INxM pin can be directly grounded in DC-coupled configuration, but the INxM pin must be grounded after the AC-coupling capacitor in the AC-coupled configuration. For the best dynamic range performance, the differential AC-coupled input setting should be used and the common-mode variation at the device input should be limited to less than 100mVpp. For more details, refer Analog Input Configurations, Mixing and Muxing of TAx5x1x Devices application report.

The device also allows for flexibility in choosing the typical input impedance on INxP or INxM from 5kΩ (default), 10kΩ, and 40kΩ based on the input source impedance selection. There can be a ±20% variation on the selected input impedance value. The higher input impedance results in slightly higher noise or lower dynamic range. Table 6-11 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]). Input impedance setting of 5 kΩ is not supported when the ADC inputs are configured for single ended mux (ADC_CHx_INSRC = 2'b10 or 2'b11) and also not supported in the high swing mode (Section 6.3.4).

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 desired low frequency signal bandwidth and amplitude. 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 1µF. 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 low distortion performance, use of low-voltage coefficient capacitors for AC coupling is recommended.

If the application uses digital PDM microphones for the recording, GPIOx, GPI1 and GPO1 pins can be reconfigured in the device to support up to four channels for the digital microphone recording (when the analog channels are not used). The device can also support simultaneous recording on two analog and two digital microphone channels or one analog channel and three digital microphone channels. Section 6.3.7 describes more details on the Digital PDM Microphone Record Channel.

The TAA5212 also supports incremental mode of ADC where the analog input channels can be used for DC measurements. This can be configured by setting the IADC_EN (P0_R81_D[7]). For more details on the incremental mode of ADC, refer Section 6.3.10.