Analog Input - Cirrus Logic CS42L42 Manual

4.1 Analog Input

The CS42L42 analog (line in/mic) input is fed to a high-dynamic range ADC path, shown in
HP ADC
HSIN±
ADC
The CS42L42 provides a mono, high-performance capture path, directly sourced from HSIN±. To optimize the path's
dynamic range and power consumption, the ADC uses analog and DSP techniques to automatically adapt to input signal
content. During normal operation, the high-performance ADC path channel selects either a high-input amplitude path or
low-noise path. With this functionality, the path's dynamic range can be optimized without the power consumption of a
single, high-amplitude, low-noise ADC path.
The ADC HSIN inputs supports fully differential, pseudodifferential, and single-ended configurations (see
Although the best performance is typically achieved with a fully differential signal input, the pseudodifferential configuration
is recommended over a traditional single-ended input configuration when possible (see
of common-mode signals or noise that may appear on the signal.
+
_
4.1.1 ADC High-Pass Filter
The ADC path, shown in Fig.
EN (see p. 154). Clearing this bit may cause clipping of the ADC digital output.
configure the corner frequency.
4.1.2 ADC Wind-Noise Filter
The defeatable, bypassable, fourth-order digital high-pass filter is enabled by
corner frequency is controlled by
4.1.3 ADC Gain Control
In traditional ADC designs, selectable gain stages or fixed-gain preamps (PGAs) commonly precede the ADC inputs.
Although these offer flexibility, they are a result of ADC input limitations. If a gain is selected too high, clipping may occur
in the ADC on loud passages. If the gain is too low to avoid clipping, sounds may be too low and SNR may suffer.
The CS42L42 ADC path achieves very high dynamic range with a very low noise floor with minimal power. Using
patent-pending circuitry that simplifies the ADC input-path configuration, the ADC fundamentally captures the entire sound
signal. The resulting SNR is typically much higher than legacy systems, without potential clipping.
The CS42L42 incorporates digital-gain capability that allows the SNR to remain constant as compared to analog gain
adjustments in legacy systems. Enabling
Additionally, the ADC_VOL
DS1083F2
ADC_HPF_EN on p. 154
ADC_HPF_CF on p. 154
HPF
Figure 4-2. Analog-Input Signal Flow
+
+
HSIN
_
_
Typically
<100 Ω
Fully Differential
Figure 4-3. Analog Input Configurations
4-2, includes a defeatable, first-order digital high-pass filter, enabled by setting
Table 3-6 lists high-pass filter specifications.
ADC_WNF_CF (see
ADC_DIG_BOOST
control (see p. 153) allows for volume control range from +12 to –96 dB, or mute.
ADC_WNF_EN on p. 154
ADC_WNF_CF on p. 154
Wind
S0
Noise
Automute
Filter
+
+
HSIN
_
_
Z
Pseudodifferential
ADC_HPF_CF
ADC_WNF_EN
p. 154). Table 3-11 lists wind-noise filter specifications.
(see p. 153) adds a +20-dB digital gain to the ADC output.
4.1 Analog Input
Fig. 4-2.
ADC_DIG_BOOST on p. 153
ADC_VOL on p. 153
EQ_BYPASS on p. 128
EQ
To SRC/DAO/SoundWire Port
Fig.
Fig. 4-2). This is due to cancelation
+
HSIN
_
Z
Single Ended
(see p. 154) is used to
(see p. 154). Its configurable
CS42L42
To Mixer
4-3).
ADC_HPF_
31