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9–11
AM700 Audio Measurement Set Service Manual
5.0V 1%
U76
U78
Voltage
Reference
±
3V Ref
TP30
5.0V Ref
VR9
3.0
2.5V Ref
Chopper
Switch
TP3
CAL SIG1
Resets at GND1,3,6,8
CAL Select
K6
K8B
TP39
OSC
10 Vout
$ 2.5V Sine
U80
Sine Wave
Oscillator
0–50 KHz
K8C
Other Channel
K7
Cal A+
Cal A–
12.288 MHz
Gated 12.288 MHz
3
6
5
12.288 MHz
to Generator
U110
Differential
RS342
Transmitter
U121C
U11D
Trigger In
J28
Trigger
Trigger
Enable
Out
To Calibration Circuitry
Offset DAC 12 Bits
8 Bits
U109
Read Back
Register
U116 Simm
72–Bit Control
Register
72
Control Lines
Data Load
Readback
Data Out
Data SRCLK
Latch
CH1 High BW Offset
CH1 High Res Offset
CH2 (B) High BW Offset
CH2 (B) High Res Offset
1
3
24
2
U81
Offset
Control DAC
(octal)
8–Bit
Power Supply
Decoupling
+15
–15
+5
3V Ref
Address
(Reset)
(Latch)
Clock
Chopper
Enable
C26D,
R255,
R256
Set
Frequency
U77 U79A
240Hz
74ALS74
555
Astable
Oscillator
+2
2.5V Ref
Oscillator Run
Latch
16–Bit Address
(Serial)
OSC RUN: Logic 0 sets Vout to 0.0V
Logic 1 = RUN
Chopper Out
120Hz 50.50 Duty Cycle
Held Low when Disabled
so Chopper Out – AGND
9
2
7
6
Figure 9–7: Analog acquisition board cal circuitry, control registers, power decoupling, and trigger input