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Abstract

An amplifier circuit with small die size and low power consumption is described. The design allows a number of switch amplifier circuits to be placed on a single chip. Each of the amplifiers contains a comparator for greater amplification, with a designed-in offset, a small pull-down current, and a diode. The comparators are biased with low current values and the need for large resistors is eliminated. Several such devices can be placed on a chip along with an edge triggered shift register to store the logic levels generated from the switch inputs. The offset, either built-in or externally supplied, sets one comparator input to an offset voltage. The switch is connected to the other input, with the diode and pull-down in parallel between this input and ground or other reference level: When the switch is open, the pull-down takes the input to ground; when the switch is closed, the diode voltage drop holds the input to a voltage above the offset. This arrangement also removes the need for key scanning routines and the pre-changing of switches. The use of relatively high gain comparators reduces the sensitivity of the amplifiers to the properties of the switches and micro-processor output ports with which they are used.

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