The analog front end module (ADC) of the TAX5XXX devices (TAC5212, TAC5211, TAA5212, TAC5412, TAC5411, TAA5412, TAA5242, TAC5242) is designed in a new architecture with 118dB Dynamic Range performance in the AC-Coupled differential input configuration. There are other device variants (TAC5112, TAC5111, TAC5312, TAC5311, TAC5142) which incorporated the same architecture with standard performance of 100dB Dynamic Range. These Dynamic Range performances are with A-weighted filter.
In this new architecture, the commonly known Programmable Gain Amplifier (PGA) is now integrated into the ADC module. The PGA gain amplification is no longer available and when additional gain is needed, the gain is applied in the digital through the Digital Volume (DVOL) register.
This application notes addresses the following questions by comparing two different architectures:
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The TAX5XXX are TI audio devices where a new Analog Digital Converter (ADC) architecture is introduced without the Programmable Gain Amplification (PGA). This new ADC architecture integrates the PGA into the ADC module, thus removing the PGA block which normally used for additional amplification. This integration allows us to increase the performance of the signal chain as if the PGA is present. When additional gain or attenuation is needed, the device has DVOL register that provides gain from -80dB to 47dB with a 0.5dB step. This new architecture gives a dynamic range of 118dB in the AC-Coupled differential input configuration with 2 Vrms full-scale input. Normally in an audio application, the front-end connection of the audio converter is a microphone or line input. Microphone such as the Electret Condenser Microphone (ECM) or the HD-Series Microphone has Signal Noise Ratio (SNR) in the 50dB-70dB range and the maximum input level (AOP) is much lower than the converter full range input. Thus, amplification is added to increase the input level into the converter full-scale level. We can look at some examples of interfacing these microphones to these converters in this appliation note.