| 摘要 |
A multi-purpose current source which provides both a PTAT and a constant current source and which requires only one precision external or laser trimmed resistance. The PTAT constant current circuit includes a differential amplifier having one input coupled to a VPTAT reference voltage and the other input coupled to a Vbg scaling circuit. The tail current for the differential amplifier is held constant at the current level of an associated constant current source based upon Vbg. Therefore, the amount of current output from the PTAT current source will be dependent upon the current of the constant current source, rather than upon a resistance value. By setting the scaling circuit appropriately, the current that flows through the output leg of the differential amplifier in the PTAT current source when the ambient temperature is equal to 25 DEG C. will be equal to one half the tail current through the differential amplifier, and thus one half the current output from the constant current source. Since the PTAT current source only requires resistors in the scaling circuit and the value of each of these scaling circuit resistors need be controlled only with respect to each other, there is no need for a precision resistance within the PTAT current source.
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