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EN 164
9.
EM6E AB
Audio Expander
F715
F714
The audio expander uses device SA572 (7770) that is intended
for high-end applications. It is used together with a low noise
OpAmp (7780).
There is an expanding factor of 2 in dB. There is a variable gain
cell (variable resistor) in the negative input of the OpAmp 7780
(NJM4565M). There is a rectifier cell that detects the input
voltage and translates into a current send to the gain cell .The
rectifier has an attack time constant and a decay time constant,
which is optimised to give the best auditive result.
If the input (V_in) rises with e.g. 2 times then the output will rise
4 times. This is because the negative input resistor formed by
the gain cell is decreased with a factor of two.
Remember that for an OpAmp V_out = V_in*((Rf+Rin)/Rin)
where Rf is constant (Rin= internal gain cell resistance).
Microcontroller
The microcontroller is an OTP Microchip PIC12C508A type
with 512-bit EPROM and six I/O lines. The controller has to be
programmed on the production line according the required
version of 433 or 864 MHz.
The main functions of the uP is reading the setting of the (4
position) slide switch within every 250 milliseconds, reading the
tuned info continuously, and start the power save mode if
necessary.
Circuit Descriptions, Abbreviation List, and IC Data Sheets
3794
3795
LO
RO
F707
3796
3797
F707
7770
SA572D
16
VCC
50V
2u2
7 GIA
G
50V
2u2
9 GIB
2772
2780
2
RCA
2776
2786
10u
16V
14 RCB
BUFFER
2774
10u 16V
4 ACA
2778
1u
12 ACB
3772
50V
2u2
1u
3 RIA
3K3
3776
50V
2u2
RECT
13 RIB
2773
3K3
GND
2777
8
Figure 9-28 Expander circuit
+8V
3755
3779
1K0
GOA
5
GOB
11
THTA
6
THTB
10
TRTA
1
TRTB
15
3778
1K0
+10V
3766
820R
DA
1K0
3750
CL
1K0
3749
POWERSAVE
6710
MUTE
BAV70
{POWERSAVE,MUTE}
Frequency setting: This is necessary when the 4-position slide
switch is changed. In an internal look-up table, the four required
frequencies for the local oscillator are stored. The output
towards the synthesiser chip in the front-end is in I2C form. The
synthesizer is the only device on the bus. During frequency
setting the "mute" is active.
Scanning of the channel switch occurs within every 250
milliseconds (in any mode).
When "tuned" is going "high" in normal mode, the channel data
should be transmitted to the synthesizer to protect the receiver
in case of hang-up situations.
Muting: The "mute" of the receiver is controlled by the IF
receiver part, but can be overridden by the microcontroller.
The "mute" action initiated by the microcontroller is necessary
during channel switching and in the standby mode. Muting has
priority on all other main tasks. The hardware mute is the result
of an "AND" function between the "Tuned" and "Stereo"
information. The "tuned" information can be read by the
microcontroller on pin 2. The same pin has to be put in output
2782
4n7
RO
3781
3782
18K
47K
F712
F712
4
6
50V
2u2
3783
7
1K8
2783
NJM4565M
8
5
7780-B
+8V
2788
4n7
LO
3787
3788
18K
47K
F713
F713
4
2
50V
2u2
3789
1
1K8
NJM4565M
2789
8
3
7780-A
+8V
CL36532008_085.eps
130503
+5V
F740
F740
7750
F741
PIC12C508A
Φ
F741
7
CTRL
F742
GP0
6
GP1
5
F742
T0CKI
4
MCLR
VPP
3
OSC2
2
OSC1
STEREO
TUNED
CLKIN
GP<0:5>
F743
F744
F743
F744
+5V
3798
22K
1765
SKR
14
12
13
11
Figure 9-29 Microcontroller circuit
BC847B
MUTE
CL36532008_086.eps
130503
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