WM8951L_07 WOLFSON [Wolfson Microelectronics plc], WM8951L_07 Datasheet - Page 16

• Manufacturer Part Number: WM8951L_07
• Description: Stereo ADC with Microphone Input and Clock Generator
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8951L
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The line inputs are biased internally through the operational amplifier to VMID. Whenever the line
inputs are muted or the device placed into standby mode, the line inputs are kept biased to VMID
using special anti-thump circuitry. This reduces any audible clicks that may otherwise be heard when
re-activating the inputs.
The external components required to complete the line input application is shown in the Figure 10.
Figure 10 Line Input Application Drawing
For interfacing to a typical CD system, it is recommended that the input is scaled to ensure that there
is no clipping of the signal. R1 = 5.6k, R2 = 5.6k, C1 = 220pF, C2 = 1µF.
R1 and R2 form a resistive divider to attenuate the 2 Vrms output from a CD player to a 1 Vrms level,
so avoiding overloading the inputs. R2 also provides a discharge path for C2, thus preventing the
input to C2 charging to an excessive voltage which may otherwise damage any equipment connected
that is not suitably protected against high voltages. C1 forms an RF low pass filter for increasing the
rejection of RF interference picked up on any cables. C2 forms a DC blocking capacitor to remove
the DC path between the WM8951L and the driving audio equipment. C2 together with the input
impedance of the WM8951L form a high pass filter.
MICROPHONE INPUT
MICIN is a high impedance, low capacitance input suitable for connection to a wide range of
monophonic microphones of different dynamics and sensitivities.
The MICIN includes programmable volume adjustments and a mute function. The scheme is shown
in Figure 11. Passive RF and active Anti-Alias filters are also incorporated within the microphone
inputs. These allow a matched interface to the multi-bit oversampling ADC and preventing high
frequencies aliasing into the audio band or otherwise degrading performance.
Figure 11 Microphone Input Schematic
There are 2 stages of gain made up of two low noise inverting operational amplifiers.
AGND
MICIN
10k
R1
VMID
R2
50k
AGND
AGND
20dB GAIN BOOST
VMID
C1
C2
PD Rev 4.1 December 2007
LINEIN
Production Data
ADC
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