Signal Synchronization And Demodulation - Teledyne T300 Operation Manual

Teledyne API – Model T300/T300M CO Analyzer
56V
Bias
Pre Amp
Photo-
detector
TEC Control
PHT DRIVE
Thermo-Electric
Cooler
Control Circuit
Compact
Programmable
Logic Device
M/R Sensor
From GFC
Wheel
Segment
Sensor
E Test Control
From CPU
via Mother
Dark Switch
Board
Control

13.4.3.1. SIGNAL SYNCHRONIZATION AND DEMODULATION

06864B DCN6314
Dark
Switch
E-Test
Generator
E Test A Gate
E Test B Gate
Dark Test Gate
Measure Gate
Measure Dark Gate
Reference Gate
Reference Dark Gate
Segment Clock
X1 Reference
÷10
X10 Clock
Phase Lock
Figure 13-13: T300/T300M Sync/Demod Block Diagram
The signal emitted by the IR photo-detector goes through several stages of amplification
before it can be accurately demodulated. The first is a pre-amplification stage that raises
the signal to levels readable by the rest of the sync/demod board circuitry. The second is
a variable amplification stage that is adjusted at the factory to compensate for
performance variations of mirrors, detectors, and other components of the optical bench
from instrument to instrument.
The workhorses of the sync/demod board are the four sample-and-hold circuits that
capture various voltage levels found in the amplified detector signal needed to determine
the value of CO MEAS and CO REF. They are activated by logic signals under the
control of a compact Programmable Logic Device (PLD), which in turn responds to the
output of the Segment Sensor and M/R Sensor as shown in Figure 13-9.
Variable Sample &
Gain Amp
Hold
Circuits
(x4)
Phase
x10
Lock
Loop
Theory of Operation
CO MEAS
Signal
Conditioner
CO Reference
Signal
Amplifiers
Conditioner
Phase Lock Warning
M/R Segment
Status LED Status LED
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