Datasheet
3-70
Power-Supply Considerations
Because the CA3130 is very useful in single-supply applica-
tions, it is pertinent to review some considerations relating to
power-supply current consumption under both single-and
dual-supply service. Figures 6A and 6B show the CA3130
connected for both dual-and single-supply operation.
Dual-supply Operation: When the output voltage at Terminal
6 is 0V, the currents supplied by the two power supplies are
equal. When the gate terminals of Q
8
and Q
12
are driven
increasingly positive with respect to ground, current flow
through Q
12
(from the negative supply) to the load is
increased and current flow through Q
8
(from the positive
supply) decreases correspondingly. When the gate terminals
of Q
8
and Q
12
are driven increasingly negative with respect
to ground, current flow through Q
8
is increased and current
flow through Q
12
is decreased accordingly.
Single-supply Operation: Initially, let it be assumed that the
value of R
L
is very high (or disconnected), and that the input-
terminal bias (Terminals 2 and 3) is such that the output termi-
nal (No. 6) voltage is at V+/2, i.e., the voltage drops across Q
8
and Q
12
are of equal magnitude. Figure 20 shows typical qui-
escent supply-current vs supply-voltage for the CA3130 oper-
ated under these conditions. Since the output stage is
operating as a Class A amplifier, the supply-current will
remain constant under dynamic operating conditions as long
as the transistors are operated in the linear portion of their
voltage-transfer characteristics (see Figure 2). If either Q
8
or
Q
12
are swung out of their linear regions toward cut-off (a
non-linear region), there will be a corresponding reduction in
supply-current. In the extreme case, e.g., with Terminal 8
swung down to ground potential (or tied to ground), NMOS
transistor Q
12
is completely cut off and the supply-current to
series-connected transistors Q
8
, Q
12
goes essentially to zero.
The two preceding stages in the CA3130, however, continue
to draw modest supply-current (see the lower curve in Figure
20) even though the output stage is strobed off. Figure 6A
shows a dual-supply arrangement for the output stage that
can also be strobed off, assuming R
L
= ∞ by pulling the poten-
tial of Terminal 8 down to that of Terminal 4.
Let it now be assumed that a load-resistance of nominal
value (e.g., 2kΩ) is connected between Terminal 6 and
ground in the circuit of Figure 6B. Let it be assumed again
that the input-terminal bias (Terminals 2 and 3) is such that
the output terminal (No. 6) voltage is at V+/2. Since PMOS
transistor Q
8
must now supply quiescent current to both R
L
and transistor Q
12
, it should be apparent that under these
conditions the supply-current must increase as an inverse
function of the R
L
magnitude. Figure 22 shows the voltage-
drop across PMOS transistor Q
8
as a function of load cur-
rent at several supply voltages. Figure 2 shows the voltage-
transfer characteristics of the output stage for several values
of load resistance.
Wideband Noise
From the standpoint of low-noise performance consider-
ations, the use of the CA3130 is most advantageous in appli-
cations where in the source resistance of the input signal is
on the order of 1MΩ or more. In this case, the total input-
referred noise voltage is typically only 23µV when the test-
circuit amplifier of Figure 7 is operated at a total supply volt-
age of 15V. This value of total input-referred noise remains
essentially constant, even though the value of source resis-
tance is raised by an order of magnitude. This characteristic
is due to the fact that reactance of the input capacitance
becomes a significant factor in shunting the source resis-
tance. It should be noted, however, that for values of source
resistance very much greater than 1MΩ, the total noise volt-
age generated can be dominated by the thermal noise con-
tributions of both the feedback and source resistors.
FIGURE 6A. DUAL POWER SUPPLY OPERATION
FIGURE 6B. SINGLE POWER SUPPLY OPERATION
FIGURE 6. CA3130 OUTPUT STAGE IN DUAL AND SINGLE
POWER SUPPLY OPERATION
3
2
8
4
7
6
R
L
Q
8
Q
12
CA3130
+
-
V+
V-
3
2
8
4
7
6
R
L
Q
8
Q
12
CA3130
+
-
V+
3
2
1
8
4
7
6
+
-
R
s
1MΩ
47pF -7.5V
0.01
µF
+7.5V
0.01µF
NOISE
VOLTAGE
OUTPUT
30.1kΩ
1kΩ
BW (-3dB) = 200kHz
TOTAL NOISE VOLTAGE (REFERRED
TO INPUT) = 23µV (TYP)
FIGURE 7. TEST-CIRCUIT AMPLIFIER (30-dB GAIN) USED
FOR WIDEBAND NOISE MEASUREMENTS
CA3130, CA3130A