temperature-compensated voltage reference that provides numerous advantages over zener diodes is described along with the implementation of thermal overload protection for monolithic circuits. The application of these and other advanced design techniques to IC voltage regulators is covered, and an example of a practical design is given.
ConsultantPuerto Vallerta, Mexico THE INTRINSIC OPERATING VOLTAGE limit of bipolar ICs is somewhat greater than the emitter-base voltage of the transistors. To date, this limit has been pushed only with digital circuitry. Techniques for constructing such devices as operational amplifiers, comparators, regulators and voltage references that will work from voltages as low as those supplied by a single nickelcadmium cell, will be offered. comes evident early in the design of low-voltage, micropower circuits where large output currents are required. The standard Darlington connection cannot be used as it raises input voltage unduly. Super-gain transistors severely restrict the maximum operating voltage, limiting the usefulness of an IC design using them as an output device. Figure 1 shows a buffer that operates from little more voltage than an unbuffered transistor. A key to its usefulness is that the emitter-base voltage of Q2 can be made sufficiently lower than that of Q1 to insure proper operation. Both voltages are predictable functions of measured process variables, and the circuit can be reproduced without special manufacturing controls.This circuit has obvious limitations that can be removed by including the refinements shown in Figure 2. A boost circuit is added to increase the bias current to Q3 with output current.This will not only increase the maximum output current for a given standby current, but also the input-voltage change required to produce it. Some linearization of the transfer function is also provided.that they do not unfavorably alter the frequency response of the inverter, at least at frequencies below a few megahertz. Figure 3 shows a class-B amplifier incorporating this design. At first glance, it would seem that the PNP output driver, consisting of three, common-emitter stages would be impossible to frequency compensate when included within a major loop. However, local feedback through Q6 and the inclusion of Q4 and R2 within the loop tends to control the frequency characteristic by making gain about equal to the NPN. Additional circuitry must be added t o control the drive current to the output PNP in saturation. This can be accomplished with minimal increase in saturated operating current.Obtaining high current gain per stage is one problem that be-
Considerable experience with such boost circuits has shownIntegrated versions of this output stage have been built to supply 5 lOmA at a total supply voltagc of 1 . l V with 2 200mV saturation voltage. Unloaded, saturation voltage is 2 l0mV and operating current is 50pA. Maximum voltage is limited only by the BVCEO of the transistors (60V -80V).Band-gap references can easily be designed to operate from a 1.3V supply. This is unnecessarily high in that it excludes the rechargable nickel-cadmium cell as a power source. The circuit in Figure 4 will provide a temperature compensated 200mV and will operate from less than 1V. It also has been corrected for the thermal nonlinearity of emitter-base voltage and the temperature drift of implanted resist...
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