Apparatus and method for converting differential voltage to fully balanced currents

An apparatus for converting a differential input voltage into two fully balanced output currents, comprising:

• a voltage/current converting circuit comprising:
• a pair of input terminals for receiving two input voltages of said differential input voltage;
• a pair of output terminals for supplying said two output currents;
• a control terminal;
• a converting circuit input section configured to convert said two input voltages to two interim output signals;
• and
• a converting circuit output section configured to convert said two interim output signals to said two output currents passing through said pair of output terminals;
• a common mode control circuit configured to control the two output currents passing through said pair of output terminals and to receive said two interim output signals, said control circuit having substantially identical circuit construction of said circuit output section and generating a control voltage signal based on said two interim output signals from said converting circuit input section, the control voltage being supplied to said control terminal of said voltage/current converting circuit;
• and
• a pair of load circuits, each of said load circuits being coupled correspondingly between each of said output terminals of said voltage/current converting circuit and a reference voltage, said pair of load circuits keeping an output common mode voltage of said output terminals of said voltage/current converting circuit at a predetermined value;
• wherein said control voltage signal is based on a sum of two control output currents that are generated from said common mode control circuit based on said two interim output signals;
• wherein said control terminal of said voltage/current converting circuit is provided in said converting circuit input section and has a high impedance, said two output control currents generated by said common mode control circuit beings summed at a common node and maintained at a substantially zero value, said control voltage signal being created at said common node.

A method for converting a differential input voltage to fully balance two output currents, the method comprising the steps of:

• converting a pair of input voltages of a differential input voltage supplied to a pair of input terminal of an OTA input section into two interim output signals;
• simultaneously providing said pair of interim output signals to a pair of input terminals of an OTA output section and a pair of input terminals of a common mode control circuit;
• generating a pair of output control current signals from said common mode control circuit based on said interim output signals from said OTA input section;
• generating a common mode control voltage signal based on a sum of said pair of output control current signals;
• and
• providing said common mode control voltage signal to a control terminal of said OTA for keeping output common mode voltage of said OTA at a reference voltage;
• wherein said step of providing the common mode control voltage comprises providing said common mode control voltage by said common mode controlling circuit to a control terminal of said OTA output section.