5.2.8 Audio Input Stage
The audio input stage of the module consists of a low noise input amplifier, which receives
its analogue input signal from pins MIC_AP and MIC_AN to a second–order ∑-∆ ADC
that outputs a 4Mbit/sec single-bit stream into the digital circuitry. The input can be
configured to be either single ended or fully differential. It can be programmed for either
microphone or line input and has a 3-bit digital gain setting of the input-amplifier in 3dB
steps to optimize it for the use of different microphones.
5.2.9 Microphone Input
Check the reference design in Figure 6 for the microphone input design.
5.2.10 Audio Output Stage
The output digital circuitry converts the signal from 16-bit per sample, linear PCM of
variable sampling frequency to a 2Mbits/sec multi-bit stream, which is fed into the analogue
The output circuit comprises a digital to analogue converter with gain setting and output
amplifier.Its class-AB output-stage is capable of driving a signal on both channels of up to
2V pk-pk- differential into a load of 16Ω. The output is available as a differential signal
between SPK_R_RP and SPK_R_RN for the left channel; and between SPK_L_LP and
SPK_L_LN for the right channel. The output is capable of driving a speaker directly if its
impedance is at least 8Ω if only one channel is connected or an external regulator is used.
The gain of the output stage is controlled by a 3-bit programmable resistive divider, which
sets the gain in steps of approximately 3dB.
The multi-bit stream from the digital circuitry is low pass filtered by a second order
bi-quad filter with a pole at 20kHz. The signal is then amplified in the fully differential
output stage, which has a gain bandwidth of typically 1MHz.
5.3 RF Interface
The module integrates a balun filter. The user can connect a 50ohms antenna directly to the
5.4 General Purpose Analog IO
The general purpose analog IOs can be configured as ADC inputs by software. Do not
connect them if not use.
5.5 General Purpose Digital IO
There are nine general purpose digital IOs defined in the module. All these GPIOs can be
configured by software to realize various functions, such as button controls, LED displays
or interrupt signals to host controller, etc. Do not connect them if not use.