| 摘要 |
A level shift circuit for converting an input signal referenced to a positive voltage to an output signal referenced to a lower voltage, such as ground. The level shift circuit includes one or more level shift stages and a reference current generator for causing a constant current to be drawn through each level shift stage. Each level shift stage includes a first transistor having a base for receiving the input signal and a collector connected to the positive voltage, a second transistor having an emitter coupled to ground, and a level shift resistor coupled between the emitter of the first transistor and the collector of the second transistor. The output signal from the collector of the second transistor is typically supplied to a TTL output stage. The reference current generator automatically compensates for temperature and power supply variations, so that the output of the level shift circuit tracks the threshold of the TTL output stage.
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