Low offset, fast response voltage controlled current source and controlling method thereof

A voltage controlled current source configured to drive an output load based on an input voltage, the voltage controlled current source comprising:

• a) a clock signal generator configured to generate a clock signal based on a square-waveform control signal, wherein said clock signal comprises a square waveform signal with a predetermined duty cycle during an active portion of said control signal, and wherein said clock signal is in an inactive state during an inactive portion of said control signal;
• b) a first operational amplifier having a first terminal configured to receive said input voltage, and a second terminal configured to receive a feedback voltage of said output load;
• c) an input offset eliminator configured to receive said clock signal, said input voltage, and said feedback voltage, wherein said input offset eliminator is configured to (i) store and then eliminate an input offset of said first operation amplifier, and to generate an error signal in accordance with an error between said input and feedback voltages when said clock signal is active and to (ii) generate said error signal in accordance with said stored input offset and said error between said input and feedback voltages when said clock signal is inactive;
• d) a sampling and holding circuit configured to receive an output signal of said first operational amplifier and said control signal, wherein energy is stored in accordance with said output signal of said first operational amplifier during said active portion of said control signal, and wherein said stored energy is maintained by said sampling and holding circuit during said inactive portion of said control signal;
• and
• e) an output circuit coupled to said sampling and holding circuit, said output circuit being configured to drive said output load during said active portion of said control signal.