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CA5130AE

15MHz, BiMOS Microprocessor Operational Amplifiers with MOSFET Input/CMOS Output

Intersil 

CA5130, CA5130A

transistors Q8, Q12 goes essentially to zero. The two preceding

stages in the CA5130, however, continue to draw modest

supply current (see the lower curve in Figure 16) 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 RL = ∞, by 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., 2kΩ) is connected between Terminal 6 and ground in

the circuit of Figure 1B. Let it further be assumed 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 Q8

must now supply quiescent current to both RL and transistor

Q12, it should be apparent that under these conditions the

supply current must increase as an inverse function of the RL

magnitude. Figure 22 shows the voltage drop across PMOS

transistor Q8 as a function of load current at several supply

voltages. Figure 15 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 CA5130 is most advantageous in applications

where 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 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 1MΩ, the total noise voltage generated can be

dominated by the thermal noise contributions of both the

feedback and source resistors.

Typical Applications

Voltage Followers

Operational amplifiers with very high input resistances, like

the CA5130, are particularly suited to service as voltage

followers. Figure 3 shows the circuit of a classical voltage

follower, together with pertinent waveforms using the

CA5130 in a split supply configuration.

A voltage follower, operated from a single supply, is shown in

Figure 4, together with related waveforms. This follower circuit

is linear over a wide dynamic range, as illustrated by the

reproduction of the output waveform in Figure 4A with input

signal ramping. The waveforms in Figure 4B show that the

follower does not lose its input-to-output phase sense, even

though the input is being swung 7.5V below ground potential.

This unique characteristic is an important attribute in both

operational amplifier and comparator applications. Figure 4B

also shows the manner in which the CMOS output stage

permits the output signal to swing down to the negative supply

rail potential (i.e., ground in the case shown). The digital-to-

analog converter (DAC) circuit, described in the following

section, illustrates the practical use of the CA5130 in a single

supply voltage follower application.

9-Bit CMOS DAC

A typical circuit of a 9-bit Digital-to-Analog Converter (DAC)

(see Note) is shown in Figure 5. This system combines the

concepts of multiple switch CMOS lCs, a low cost ladder

network of discrete metal-oxide film resistors, a CA5130 op

amp connected as a follower, and an inexpensive monolithic

regulator in a simple single power supply arrangement. An

additional feature of the DAC is that it is readily interfaced

with CMOS input logic, e.g., 10V logic levels are used in the

circuit of Figure 5.

NOTE: “Digital-to-Analog Conversion Using the Intersil CD4007A

CMOS lC”, Application Note AN6080.

+7.5V

Rs

3

1MΩ

2

7

+

-

4

8

1

47pF -7.5V

0.01µF

6

0.01

µF

NOISE

VOLTAGE

OUTPUT

30.1kΩ

BW (-3dB) = 200kHz

TOTAL NOISE VOLTAGE (REFERRED

1kΩ

TO INPUT) = 23µV (TYP)

FIGURE 2. CA5130 OUTPUT STAGE IN DUAL AND SINGLE

POWER SUPPLY OPERATION

8

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