4
Applying the HA-4900 Series Comparators
Supply Connections
This device is exceptionally versatile in working with most available
power supplies. The voltage applied to the V+ and V- terminals
determines the allowable input signal range; while the voltage applied
to the V
L
+ and V
L
- determines the output swing. In systems where
dual analog supplies are available, these would be connected to V+
and V-, while the logic supply and return would be connected to
V
LOGIC
+ and V
LOGIC
-. The analog and logic supply commons can
be connected together at one point in the system, since the comparator
is immune to noise on the logic supply ground. A negative output
swing may be obtained by connecting V
L
+ to ground and V
L
- to a
negative supply. Bipolar output swings (15V
P-P
, Max) may be
obtained using dual supplies. In systems where only a single logic
supply is available (+5V to 15V), V+ and V
LOGIC
+ may be
connected together to the positive supply while V- and V
LOGIC
- are
grounded. If an input signal could swing negative with respect the V-
terminal, a resistor should be connected in series with the input to limit
input current to < 5mA since the C-B junction of the input transistor
would be forward biased.
Unused Inputs
Inputs of unused comparator sections should be tied to a differential
voltage source to prevent output “chatter.”
Crosstalk
Simultaneous high frequency operation of all other channels in the
package will not affect the output logic state of a given channel,
provided that its differential input voltage is sufficient to define a
given logic state (ΔV
IN
≥ ±V
OS
). Low level or high impedance
input lines should be shielded from other signal sources to reduce
crosstalk and interference.
Power Supply Decoupling
Decouple all power supply lines with 0.01μF ceramic capacitors to
ground line located near the package to reduce coupling between
channels or from external sources.
Response Time
Fast rise time (<200ns) input pulses of several volts amplitude may
result in delay times somewhat longer than those illustrated for
100mV steps. Operating speed is optimized by limiting the
maximum differential input voltage applied, with resistor-diode
clamping networks.
Typical Applications
Data Acquisition System
In this circuit the HA-4900 series is used in conjunction with a D
to A converter to form a simple, versatile, multi-channel analog
input for a data acquisition system. In operation the processor first
sends an address to the D to A, then the processor reads the digital
word generated by the comparator outputs. To perform a simple
comparison, the processor sets the D to A to a given reference
level, then examines one or more comparator outputs to determine
if their inputs are above or below the reference. A window
comparison consists of two such cycles with 2 reference levels set
by the D to A. One way to digitize the inputs would be for the
processor to increment the D to A in steps. The D to A address, as
each comparator switches, is the digitized level of the input. While
stairstepping the D to A is slower than successive approximation,
all channels are digitized during one staircase ramp.
Schematic Diagram
Q
9D
BIAS 2
ONE FOURTH ONLY
R
20D
1kΩ
R
20C
1kΩ
R
20B
1kΩ
R
20A
1kΩ
Q
9C
Q
9B
Q
9A
R
21
1kΩ
Q
10
D
9A
BIAS 1
Q
5
Q
4
D
4A
D
4B
Q
4C
Q
3
R
16
540Ω
PR
1
200kΩ
R
10
4kΩ
Q
2
Q
1
R
9
4kΩ
BIAS 3 BIAS 4
Q
11
+IN
Q
17
Q
18
Q
12
Q
13
R
1
500Ω
R
2
13kΩ
R
3
1kΩ
Q
19
Q
20
Q
14
R
4
1kΩ
Q
21
Q
22
-IN
M
N1
R
7
2.5kΩ
R
6
2.5kΩ
Q
16
Q
7
Q
23
R
5
360Ω
M
N2
M
N3
Q
24
Q
25
R
18
664Ω
Q
38
M
N4
D
45
D
11A
Q
26
R
17
19kΩ
R
14
5kΩ
Q
33
Q
34
Q
36
Q
37
Q
30
Q
28
R
11
8kΩ
R
15
8kΩ
Q
31
R
23
100Ω
R
24
14kΩ
D
29B
Q
29
Q
29A
R
22
100Ω
R
12
8kΩ
Q
32
M
N6
M
N5
V
LOGIC
-
OUT
V
LOGIC
+
V-
V+
Q
15
D
35
D
39
HA-4900, HA-4902, HA-4905
