Tektronix TLA Series, Service Manual

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Theory of Operation
3- 2
TLA Series Digitizing Oscilloscope Modules Service Manual
Attenuators.
Signals applied to each channel input (CH 1, CH 2, CH 3, and
CH 4) connect to an attenuator. The Main Processor System controls the
attenuators. The attenuators select input coupling, termination, bandwidth, offset,
and full scale range. Outputs from each attenuator drive the Acquisition System
and Trigger circuits.
Acquisition System. The Acquisition System amplifies the input signals, samples
them, and converts them to digital signals with 8-bit resolution. The system
controls the acquisition process under direction of the Main Processor System.
Voltage Controlled Oscillator (VCO).
Master clocks for the Acquisition System are
generated by the Voltage Controlled Oscillator (VCO). The VCO circuit is a
phase locked loop that is referenced to a 10 MHz clock provided by the
mainframe.
Trigger. The Trigger circuit produces trigger signals to control the Acquisition
System timebase. Trigger signals are selected from the following sources:
H
Attenuator — internal triggering
H
Intermodule Triggers — triggering from the communications bus
Intermodule Triggers. The Intermodule Triggers circuit routes system-generated
TTLTRG and ECLTRG trigger signals to the Trigger circuit. Under control of
the Main Processor System, the Intermodule Triggers circuit selects which
TTLTRG and ECLTRG trigger signals are active, and defines the arming and
triggering parameters.
The Processor Board (A1) controls instrument hardware, signal acquisition, and
communications functions. Two 100-pin ribbon cables provide interconnections
with the Acquisition Board (A2) for power supplies, waveform data, and control
signals.
The Processor Board (A1) consists of the following circuits:
H
Main Processor System
H
DSP Processor System
H
Backplane Interface
H
Power Supplies
Processor Board (A1)