ca3160t Intersil Corporation, ca3160t Datasheet - Page 6

• Manufacturer Part Number: ca3160t
• Description: 4mhz, Bimos Operational Amplifier With Mosfet Input/cmos Output
• Manufacturer: Intersil Corporation

magnitude as those encountered in an operational amplifier
employing a bipolar transistor input stage. The 2V differential
voltage example represents conditions when the amplifier
output state is “toggled”, e.g., as in comparator applications.
Power Supply Considerations
Because the CA3160 is very useful in single supply
applications, it is pertinent to review some considerations
relating to power supply current consumption under both
single and dual supply service. Figures 1A and 1B show the
CA3160 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
increasingly positive with respect to ground, current flow
through Q
increased and current flow through Q
supply) decreases correspondingly. When the gate terminals
of Q
to ground, current flow through Q
flow through Q
Single supply operation: Initially, let it be assumed that the
value of R
terminal bias (Terminals 2 and 3) is such that the output
terminal (No. 6) voltage is at V+/2, i.e., the voltage-drops
across Q
typical quiescent supply-current vs supply voltage for the
CA3160 operated 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 17).
If either Q
cutoff (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
current to series connected transistors Q
essentially to zero. The two preceding stages in the CA3160,
however, continue to draw modest supply-current (see the
lower curve in Figure 18) even though the output stage is
strobed off. Figure 1A shows a dual-supply arrangement for the
output stage that can also be strobed off, assuming R
pulling the potential of Terminal 8 down to that of Terminal 4.
Let it now-be assumed that a load resistance of nominal value
(e.g., 2k ) is connected between Terminal 6 and ground in the
circuit of Figure 1B. Let it further 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
must now supply quiescent current to both R
Q
supply current must increase as an inverse function of the R
magnitude. Figure 20 shows the voltage-drop across PMOS
transistor Q
12
, it should be apparent that under these conditions the
8
and Q
8
8
12
L
and Q
or Q
8
is very high (or disconnected), and that the input-
12
as a function of load current at several supply
(from the negative supply) to the load is
12
are driven increasingly negative with respect
12
12
is decreased accordingly.
are swung out of their linear regions toward
12
are of equal magnitude. Figure 18 shows
is completely cut off and the supply
6
8
is increased and current
8
8
and Q
(from the positive
8
, Q
L
12
12
and transistor
goes
are driven
L
CA3160, CA3160A
= , by
8
L
voltages. Figure 17 shows the voltage transfer characteristics of
the output stage for several values of load resistance.
Wideband Noise
From the standpoint of low-noise performance considerations,
the use of the CA3160 is most advantageous in applications
where in the source resistance of the input signal is on the
order of 1M or more. In this case, the total input-referred
noise voltage is typically only 40 V when the test circuit
amplifier of Figure 2 is operated at a total supply voltage of
15V. This value of total input-referred noise remains
essentially constant, even though the value of source
resistance 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 resistance. It should be noted, however, that for values
of source resistance very much greater than 1M , the total
noise voltage generated can be dominated by the thermal
noise contributions of both the feedback and source resistors.
FIGURE 1. CA3160 OUTPUT STAGE IN DUAL AND SINGLE
FIGURE 1B. SINGLE POWER SUPPLY OPERATION
FIGURE 1A. DUAL POWER SUPPLY OPERATION
2
3
2
3
POWER SUPPLY OPERATION
CA3160
CA3160
+
+
-
-
8
8
Q
Q
Q
Q
12
12
8
8
V+
V-
4
4
7
7
OUTPUT
OUTPUT
STAGE
STAGE
V+
NEGATIVE
SUPPLY
6
6
R
R
L
L