Voltage follower circuit having improved dynamic range

Abstract

A voltage follower circuit includes a differential amplifier which has first and second transistors. The output of the collector of the second transistor is fed to the base of the second transistor as a feedback input through a third transistor and a diode. The diode operates as a direct current level-shift circuit. A video signal is fed to the base of the first transistor, and the output of the voltage follower circuit is taken from the base of the second transistor.

We claim: 
     
       1. A voltage follower circuit comprising: a differential amplifier including a first and a second transistor whose emitters are connected to each other, a first constant current source connected to said emitters and a second constant current source connected to the collector of said second transistor,   a third transistor, having a base connected to the collector of said second transistor, the first and third transistors having collectors connected to a reference voltage.   a diode connected between the emitter of said third transistor and the base of said second transistor,   a third constant current source connected to the emitter of said third transistor, and   a fourth constant current source connected to the base of said second transistor wherein the base of said first transistor receives an input signal and wherein the base of said second transistor is an output terminal.   
     
     
       2. A voltage follower circuit as claimed in claim 1, further comprising a load resistor connected to said output terminal. 
     
     
       3. A voltage follower circuit as claimed in claim 1, wherein each constant current source comprises a resistor and a transistor connected serially to said resistor. 
     
     
       4. A voltage follower circuit as claimed in claim 1, wherein each of said first and second constant current sources comprises a resistor, and each of said third and fourth constant current sources comprises a resistor and a transistor connected serially to said resistor. 
     
     
       5. A voltage follower circuit as claimed in claim 1, wherein said diode is a transistor whose base and collector are connected to the base of said second transistor, and whose emitter is connected to the emitter of said third transistor. 
     
     
       6. A voltage follower circuit comprising: a differential amplifier including a first and a second transistor whose emitters are connected to each other, a first constant current source connected to said emitters and a second constant current source connected to the collector of said second transistor,   a third transistor, having a base connected to the collector of said second transistor, the first and third transistor having collectors connected to a reference voltage,   a voltage level-shifting connected between the emitter of said third transistor and the base of said second transistor, and   a third constant current source connected to the emitter of said third transistor,   a fourth constant current source connected to the base of said second transistor wherein the base of said first transistor receives an input signal and wherein the base of said second transistor is an output terminal.