| 摘要 |
ROGERS BERESKIN /A PARR CANADA 0374-069 Title: Switch with frequency compensation, Early voltage compensation and enable indicator Inventor: John R. Francis The switch has a cross-point. The cross-point has an input buffer, a level shift and an output buffer. The input and output buffers are BJT's, the level shift is two diode connected BJT's. The voltage drops across the buffers are designed to match the voltage drops across the diodes. The cross-point is enabled by a current source forcing current through the diodes. The matching of the voltage drops is effected by the Early voltage of the BJT's as they are operated at different Vce's. An Early voltage determinator determines the effect of the Early voltage and adjusts the current flowing from the current source to force differing bias currents through the input buffer and the diodes to make the sum of the Vbe's of each more independent of Early voltage. The output impedance of the current source and the impedance of the cross-point form a resistor-capacitor network. Where the ft Of the current source is sufficiently low, the network has a pole-zero combination within the otherwise usable bandwidth of the switch. The current source has a first BJT at its output. A frequency compensating BJT is connected to the base of the first BJT, bringing the pole and zero closer together and shifting the pole-zero combination towards the upper limit of the otherwise usable bandwidth of the switch. A tally output is provided from the biasing network of the switch. The tally output provides an indication of the operating state, enabled or disabled, of the switch.
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