Analog-To-Digital Converter - Tektronix 11A52 Service Manual

Theory of Operation
Analog-to-Digital Converter
The Analog-to-Digital converter (A/D) is contained in the TLC540 (U750). The TLC540 is a complete 8-bit,
switched-capacitor, successive-approximation A/D converter. It has a serial interface to the microprocessor
with a 12-channel analog multiplexer that can be used to sample any one of 11 inputs or an internal "self-test"
voltage. The sample/hold operates under microprocessor control.
The AID converter signal lines are described below:
TABLE 2-1
The ND Converter Signal Lines
Name pin# Description
AO 1
(not used)
Al 2
(not used)
A2 3 Analog input for Fuse check.
A3
4
(not used)
A4 5
Analog input for CH 1 Probe data
AS 6
Analog input for CH 2 Probe data
A6 7
(not used)
A7 8
(not used)
AS 9
Analog input for MINTST (AlA2 self-test)
A9
--
AlO 12
Analog input for MAJTST (AlAl self-test)
All
--
(internal self-test of A/D
=
1/2[ (REF+) + (REF-) voltage]
Address in
17 Serial address input used to select A/D input AO-All
Sys Clock 19
Runs the AID conversion hardware
I/0
Clock
18 Serial
I/O
clock input
CS(L)
15 Enables A/D converter
I/0
and conversion
Data out 16 Serial data output
REF+ 14 Positive reference for the AO-All inputs
REF-
13
Negative reference for the AO-All inputs
The AO-All inputs are referenced to the input signal lines REF+ and REF-. The REF+ line is connected to +SA
and the REF- line is connected to ground. Therefore, inputs near GND potential will convert to values near the
digital value OOhex and inputs near +SA potential will convert to values near the digital value FFhex. A
correctly operating A/D converter will give a self-test value of near 80hex for the All internal input shown
above. · ·
2-8
11A52 Extended Service Manual