WM8951L_07 WOLFSON [Wolfson Microelectronics plc], WM8951L_07 Datasheet - Page 17

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

Production Data
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The 1
series with MICIN the gain of stage can be adjusted. For example adding Rmic = 40K sets the gain
of stage 1 to x1 (0dB). The equation below can be used to calculate the gain versus Rmic.
Or alternatively to calculate the value of Rmic to achieve a given gain, G1.
The internal 50k and 10k resistors have a tolerance of 15%. For Rmicext = 90k G = 0.5 (-6dB) and
for Rmicext = 0 G = x10 (14dB).
The 2
gain for low sensitivity microphones.
The microphone input can therefore be configured with a variable gain of between -6dB and 14dB on
the 1
input signal in the range –6dB to 34dB to be catered for.
The ADC Full Scale input is 1.0V rms at AVDD1/2 = 3.3 volts. Any voltage greater than full scale will
overload the ADC and cause distortion. Note that the full scale input tracks directly with AVDD1/2.
Stage 1 and Stage 2 gains should be configured so that the ADC receives a maximum signal equal
to its full scale for maximising the signal to noise.
The software control for the MICIN is shown in Table 3. Note that the Microphone Mute only mutes
the input to the ADC, this will still allow the Microphone Input signal to pass to the line output in
Sidetone Mode.
Table 3 Microphone Input Software Control
The microphone input is biased internally through the operational amplifier to VMID. Whenever the
line inputs are muted the MICIN input is kept biased to VMID using special anti-thump circuitry. This
reduces any audible clicks that may otherwise be heard when re-activating the input.
The application drawing for the microphone is shown in Figure 12.
Figure 12 Microphone Input and Bias Application Drawing
0000100
Analogue Audio
Path Control
REGISTER
ADDRESS
MICROPHONE
st
st
nd
stage, and an additional fixed 0dB or 20dB on the 2
stage comprises a nominal gain of G1 = 50k/10k = 5. By adding an external resistor (Rmic) in
stage comprises a 0dB gain stage that can be software configured to provide a fixed 20dB of
FROM
G1 = 50k/ (Rmic + 10k)
Rmic = (50k/G1) – 10k
0
1
BIT
AGND
MICBOOST
MUTEMIC
LABEL
R1
R2
AGND
AGND
0
1
DEFAULT
C1
C2
MICBIAS
nd
1 = Enable Boost
0 = Disable Boost
Line Input Mute to ADC
1 = Enable Mute
0 = Disable Mute
Microphone Input Level Boost
stage. This allows for all gains to the
Rmic
DESCRIPTION
PD Rev 4.1 December 2007
MICIN
WM8951
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