M41T00AUDD1E STMICROELECTRONICS [STMicroelectronics], M41T00AUDD1E Datasheet - Page 31

• Manufacturer Part Number: M41T00AUDD1E
• Description: Serial real-time clock with audio
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

7.1
7.1.1
Gain
The programmable gain stage follows the band pass filter. It provides between –33 and
+12dB of gain, in 3dB steps (+/-1dB per step). The gain is selected by the GAIN bits, D3-D0
of register 08h, as listed in
be cut off altogether.
At the first power up, GAIN will be initialized to its lowest value, 0, corresponding to a gain of
–33dB. Furthermore, MUTE will be set thus cutting off all audio.
On subsequent power ups, GAIN is unaffected, but the MUTE bit is always set to turn off the
audio at power up.
The final section is the output driver. It has a differential output capable of driving 300mW
into an 8Ω load.
The overall gain of the M41T00AUD is defined as the ratio of the AC output voltage, A
and the AC input voltage, S
blocks any DC in the input signal.
Equation 1
A
Each of the output levels is determined by the ratio of the feedback and input resistors along
with the GAIN value.
where A
yields:
With R1 = 2*R2, this reduces to A
Table 7
indicated 0.1uF capacitor). For GAIN set to B (0dB, A
to the input (
Gain tolerance
Two tolerance parameters apply to the gain levels. As shown in
limits are listed for four of the GAIN values (4, 5, Bh and Eh). For GAIN=Bh, the tolerance is
±1dB. This means the end-to-end gain of the part, with R1 = 2*R2, will be 0±1dB. For
GAIN=4, 5 and Eh, the tolerance is ±2dB. At each of these three settings, as shown in table
7, the gain will be within 2dB of the listed typical value. For GAIN =E, the end-to-end gain
will be between +7 and +11 dB (9±2dB).
OUT
is measured between the output pins AOUT
reflect overall gain of the circuit (at mid-band frequencies, about 1kHz with the
V
is the scalar gain as shown in
A
±
OUT
1dB).
= S
IN
x A
V
Table
IN
x R2/R1
, as shown in
AOUT
Overall gain = A
AOUT
4. A MUTE bit, D4 of the same register, allows the audio to
A
OUT
OUT
-
–
= S
+
(
= AOUT
-
=
= S
Table
S
IN
-
IN
S
Figure
IN
x A
IN
x A
x A
7. Substituting these into Equation 1 above
x A
V
+
V
. Thus, when R1 = 2*R2, the gain levels in
OUT
-
V
x R2/R1) = 2 S
+
V
16. The 0.1uF input coupling capacitor
AOUT
x R2/R1
and AOUT
x R2/R1
/ S
V
= 1), the output voltage will be equal
IN
–
–
.
Table
IN
x A
V
7, upper and lower
x R2/R1
OUT
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