Its internal structure is comprised of both bipolar transistors and Mosfet. Moreover, it supports Mosfet type input and bipolar output. This P-channel Mosfet in the input circuit allows high impedance and a wide range of common-mode input voltage. Furthermore, it supports a wide range of operating voltage due to bipolar output transistors.
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The schematic diagram details one amplifier section of the CA It consists of a differential amplifier stage using PMOS transistors Q9 and Q10 with gate-to-source protection against static discharge damage provided by zener diodes D3,D4,and D5.
Constant current bias is applied to the differential amplifier from transistors Q2 and Q5 connected as a constant current source. This assures a high common-mode rejection ratio. The output of the differential amplifier is coupled to the base of gain stage transistor Q13 by means of an NPN current mirror that supplies the required differential-to-single-ended conversion.
Provision for offset null for types in the 14 lead plastic package E1 suffix is provided through the use of this current mirror. The gain stage transistor Q13 has a high impedance active load Q3 and Q4 to provide maximum open-loop gain.
The collector of Q13 directly drives the base of the compound emitter-follower output stage. Pulldown for the output stage is provided by two independent circuits: 1 constant-current- connected transistors Q14 and Q15 and 2 dynamic current- sink transistor Q16 and its associated circuitry.
When this condition exists, transistors Q21 and Q16 are turned on causing Q16 to sink current from the output terminal to V-.
This current always flows when the output is in the linear region, either from the load resistor or from the emitter of Q18 if no load resistor is present. The purpose of this dynamic sink is to permit the output to go within 0. This may be accomplished by placing a resistor Approx. Output Circuit Considerations Figure 24 shows output current-sinking capabilities of the CA at various supply voltages.
Output voltage swing to the negative supply rail permits this device to operate both power transistors and thyristors directly without the need for level-shifting circuitry usually associated with the series of operational amplifiers. Figure 3 shows some typical configurations. Note that a series resistor, RL, is used in both cases to limit the drive available to the driven device.
Moreover, it is recommended that a series diode and shunt diode be used at the thyristor input to prevent large negative transient surges that can appear at the gate of thyristors, from damaging the integrated circuit. However, a series current- limiting resistor is recommended to limit the maximum input terminal current to less than 1mA to prevent damage to the input protection circuitry.
Moreover, some current-limiting resistance should be provided between the inverting input and the output when the CA is used as a unity-gain voltage follower. This resistance prevents the possibility of extremely large input- signal transients from forcing a signal through the input- protection network and directly driving the internal constant- current source which could result in positive feedback via the output terminal.
As the output supplies load current, device dissipation will increase, rasing the chip temperature and resulting in increased input current. Figure 4 shows typical input-terminal current versus ambient temperature for the CA
CA3240 BiMOS Op Amp with MOSFET Input/Bipolar Output