Patent ID: 6963238
Filing Date: 2005-11-08
Classification: H03F

Abstract:
1. A level shift circuit having a level shift function, in which since the level shift circuit is connected to a current adding type digital/analog converter constituted by a plurality of constant current sources which have been weighted by bits and having two differential outputs such as a positive-phase output terminal and a negative-phase output terminal, an arbitrary voltage is added to an analog output voltage of the current adding type digital/analog converter so as to be outputted, the level shift circuit comprising: a first operational amplifier; a second operational amplifier; a first resistor, connected between the positive-phase output terminal of the current adding type digital/analog converter and an inverting input terminal of said first operational amplifier; a second resistor, connected between the inverting input terminal of the first operational amplifier and a positive-phase output terminal thereof; a third resistor, connected between the negative-phase output terminal of the current adding type digital/analog converter and a positive-phase input terminal of the first operational amplifier; a fourth resistor, connected between the positive-phase input terminal of the first operational amplifier and an inverting output terminal thereof; a fifth resistor, connected between the positive-phase output terminal of the first operational amplifier and the positive-phase input terminal of the second operational amplifier; a sixth resistor, having the same resistance value as that of the fifth resistor, and connected between the inverting output terminal of the first operational amplifier and the positive-phase input terminal of said second operational amplifier; a first voltage-controlled current source connected to the positive-phase output terminal of the current adding type digital/analog converter; and a second voltage-controlled current source connected to the negative-phase output terminal of the current adding type digital/analog converter; wherein the inverting input terminal of the second operational amplifier is connected to a third input terminal; and an output of the second operational amplifier is connected to both the first voltage-controlled current source and the second voltage-controlled current source.