Stanford Research Systems SR124 Operation And Service Manual page 26

2 – 4
A / I
PREAMP
+
B
–
A–B
A
FLOAT
INTERNAL
REAR VCO
EXT. IN
PLL
2.2.1.1 Internal mode
2.2.1.2 Rear-panel VCO mode
2.2.1.3 External mode
AC GAIN
INPUT
FILTER
AC VOLT
LOCK-IN
PHASE
SHIFT
SQUARE
VCO
90°
0°
DC
BIAS
Figure 2.1: The SR124 block diagram.
Operating in Internal mode, the SR124 oscillator is programmed by
an internally-generated DC voltage source. Within the oscillator
frequency range (set by the Range knob), the oscillator frequency is
controlled with the front-panel control knob or remote command.
When configured for Rear VCO operation, the SR124 oscillator pro-
gramming voltage is directly controlled by the user through a rear-
panel BNC input. Input voltage from 0 to 10 V will set the oscillator
frequency between the lower and upper limits set by the range, with
an approximately linear transfer function.
The SR124 oscillator can lock to an external reference signal applied
to the Ext. In BNC connector. This input operates in two distinct
modes, sine input and TTL input (indicated by the TTL indicator
just above the connector).
TIME
PSD DC GAIN
CONSTANT
OFFSET
+
×1
–
SR124 Analog Lock-In Amplifier
Introduction
SIGNAL
MONITOR
600 Ω
OUTPUT
+
×10
–
600 Ω
REF OUT
REF
ATTEN
50 Ω