Datasheet

5
Cascade-connected PMOS transistors Q2, Q4 are the
constant-current source for the input stage. The biasing circuit
for the constant-current source is subsequently described.
The small diodes D
5
through D
8
provide gate-oxide protection
against high-voltage transients, including static electricity
during handling for Q
6
and Q
7
.
Second-Stage
Most of the voltage gain in the CA3130 is provided by the
second amplifier stage, consisting of bipolar transistor Q
11
and its cascade-connected load resistance provided by
PMOS transistors Q
3
and Q
5
. The source of bias potentials
for these PMOS transistors is subsequently described. Miller
Effect compensation (roll-off) is accomplished by simply
connecting a small capacitor between Terminals 1 and 8. A
47pF capacitor provides sufficient compensation for stable
unity-gain operation in most applications.
Bias-Source Circuit
At total supply voltages, somewhat above 8.3V, resistor R
2
and zener diode Z
1
serve to establish a voltage of 8.3V across
the series-connected circuit, consisting of resistor R
1
, diodes
D
1
through D
4
, and PMOS transistor Q
1
. A tap at the junction
of resistor R
1
and diode D
4
provides a gate-bias potential of
about 4.5V for PMOS transistors Q
4
and Q
5
with respect to
Terminal 7. A potential of about 2.2V is developed across
diode-connected PMOS transistor Q
1
with respect to Terminal
7 to provide gate bias for PMOS transistors Q
2
and Q
3
. It
should be noted that Q
1
is “mirror-connected (see Note 8)” to
both Q
2
and Q
3
. Since transistors Q
1
, Q
2
, Q
3
are designed to
be identical, the approximately 200µA current in Q
1
establishes a similar current in Q
2
and Q
3
as constant current
sources for both the first and second amplifier stages,
respectively.
At total supply voltages somewhat less than 8.3V, zener
diode Z
1
becomes nonconductive and the potential,
developed across series-connected R
1
, D
1
-D
4
, and Q
1
,
varies directly with variations in supply voltage.
Consequently, the gate bias for Q
4
, Q
5
and Q
2
, Q
3
varies in
accordance with supply-voltage variations. This variation
results in deterioration of the power-supply-rejection ratio
(PSRR) at total supply voltages below 8.3V. Operation at
total supply voltages below about 4.5V results in seriously
degraded performance.
Output Stage
The output stage consists of a drain-loaded inverting
amplifier using CMOS transistors operating in the Class A
mode. When operating into very high resistance loads, the
output can be swung within millivolts of either supply rail.
Because the output stage is a drain-loaded amplifier, its gain
is dependent upon the load impedance. The transfer
characteristics of the output stage for a load returned to the
negative supply rail are shown in Figure 2. Typical op amp
loads are readily driven by the output stage. Because large-
signal excursions are non-linear, requiring feedback for good
waveform reproduction, transient delays may be
encountered. As a voltage follower, the amplifier can achieve
0.01% accuracy levels, including the negative supply rail.
NOTE:
8. For general information on the characteristics of CMOS
transistor-pairs in linear-circuit applications, see File Number
619, data sheet on CA3600E “CMOS Transistor Array”.
3
2
7
4
815
6
BIAS CKT.
COMPENSATION
(WHEN REQUIRED)
A
V
≈ 5X
A
V
≈
A
V
≈
6000X
30X
INPUT
+
-
200µA 200µA
1.35mA
8mA
0mA
V+
OUTPUT
V-
STROBE
C
C
OFFSET
NULL
CA3130
(NOTE 7)
(NOTE 5)
NOTES:
6. Total supply voltage (for indicated voltage gains) = 15V with input
terminals biased so that Terminal 6 potential is +7.5V above
Terminal 4.
7. Total supply voltage (for indicated voltage gains) = 15V with
output terminal driven to either supply rail.
FIGURE 1. BLOCK DIAGRAM OF THE CA3130 SERIES
22.5
GATE VOLTAGE (TERMINALS 4 AND 8) (V)
OUTPUT VOLTAGE (TERMINALS 4 AND 8) (V)
17.5 2012.5 15107.52.5 50
2.5
7.5
5
10
15
12.5
17.5
0
SUPPLY VOLTAGE: V+ = 15, V- = 0V
T
A
= 25
o
C
LOAD RESISTANCE = 5kΩ
500Ω
1kΩ
2kΩ
FIGURE 2. VOLTAGE TRANSFER CHARACTERISTICS OF
CMOS OUTPUT STAGE
CA3130, CA3130A