The Functional Sr844 - Stanford Research Systems SR844 User Manual

2-8 SR844 Basics

The Functional SR844

The functional block diagram of the SR844 RF Lock-In Amplifier is shown below. A
short description of each block follows .
50 Ω
1 MΩ
Signal Input
PreAmp
Mixer
20 MHz XTAL
Reference
Auto-threshold
External
Reference
Input
50 Ω
SR844 RF Lock-In Amplifier
SR844 Block Diagram
RF Signal Path
200 MHz
LPF
I. F. Section
180 kHz Variable IF
LPF Gain
Reference Channel
Int Ref
Synthesizer
Ext Ref
Phase
Comparator Comparator
20 dB 20 kHz
Attenuator HPF
X-IF
Anti-alias A to D
DSP
Filter Converter
Y-IF
Loop Filter Error 200-400 MHz
Amplifier VCO
20 dB Gain
D to A
Front Panel
Converter
Outputs
IF Chop
X Ref
IF Chop IF Chop
Y Ref
Ref
Divider Chain
CH1
CH2