3-1/2 DIGIT A/D CONVERTERS
TC7106
TC7106A
TC7107
TC7107A
PIN DESCRIPTION
(Cont.)
Pin No.
Pin No.
40-Pin PDIP 40-Pin PDIP
(Normal)
(Reverse)
34
(7)
Symbol
C
REF
+
Description
A 0.1µF capacitor is used in most applications. If a large common-
mode voltage exists (for example, the V
–
pin is not at analog
IN
common), and a 200mV scale is used, a 1µF capacitor is recom-
mended and will hold the roll-over error to 0.5 count.
See pin 36.
The analog input required to generate a full-scale output (1999
counts). Place 100mV between pins 35 and 36 for 199.9mV
full-scale. Place 1V between pins 35 and 36 for 2V full scale. See
paragraph on REFERENCE VOLTAGE.
Lamp test. When pulled HIGH (to V
+
) all segments will be turned on
and the display should read –1888. It may also be used as a negative
supply for externally-generated decimal points. See paragraph under
TEST for additional information.
See pin 40.
See pin 40.
Pins 40, 39, 38 make up the oscillator section. For a 48kHz clock
(3 readings per section), connect pin 40 to the junction of a 100kΩ
resistor and a 100pF capacitor. The 100kΩ resistor is tied to pin 39
and the 100pF capacitor is tied to pin 38.
35
36
(6)
(5)
–
V
REF
V
+
REF
37
(4)
Test
38
39
40
(3)
(2)
(1)
OSC
3
OSC
2
OSC
1
GENERAL THEORY OF OPERATION
DUAL SLOPE CONVERSION PRINCIPLES
(All Pin Designations Refer to the 40-Pin DIP)
The TC7106A and TC7107A are dual slope, integrating
analog-to-digital converters. An understanding of the dual
slope conversion technique will aid in following the detailed
operation theory.
The conventional dual slope converter measurement
cycle has two distinct phases:
• Input Signal Integration
• Reference Voltage Integration (Deintegration)
The input signal being converted is integrated for a fixed
time period (T
SI
). Time is measured by counting clock
pulses. An opposite polarity constant reference voltage is
then integrated until the integrator output voltage returns to
zero. The reference integration time is directly proportional
to the input signal (T
RI
). (Figure 2A).
In a simple dual slope converter a complete conversion
requires the integrator output to “ramp-up” and “ramp-
down.”
A simple mathematical equation relates the input signal,
reference voltage and integration time:
T
SI
V
R
T
RI
1
RC
RC
0 V
IN
(t)dt =
where:
V
R
= Reference Voltage
T
SI
= Signal Integration Time (Fixed)
T
RI
= Reference Voltage Integration Time (Variable)
For a constant V
IN
:
T
V
IN
= V
R RI
T
SI
C
ANALOG
INPUT
SIGNAL
INTEGRATOR
–
+/–
SWITCH
DRIVER
REF
VOLTAGE
PHASE
CONTROL
CONTROL
LOGIC
POLARITY CONTROL
CLOCK
INTEGRATOR
OUTPUT
COMPARATOR
–
DISPLAY
VIN
VIN
VARIABLE
REFERENCE
INTEGRATE
TIME
≈
VFULL SCALE
≈
1/2 VFULL SCALE
∫
FIXED
SIGNAL
INTEGRATE
TIME
Figure 2A. Basic Dual Slope Converter
3-188
TELCOM SEMICONDUCTOR, INC.
+
COUNTER
+
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
