Active auto zero circuit for programmable time continuous open loop amplifiers

A method of canceling offset between first and second stages of an open loop differential amplifier having a variable gain, the method comprising:

• (a) disconnecting first and second differential inputs to said first and second stages from an input source;
• (b) setting said variable gain to a maximum value;
• (c) connecting said first and second differential inputs to a common voltage source;
• (d) detecting output offset voltage on first and second differential outputs of said amplifier;
• (e) computing an adjusted bias current to cancel said output offset voltage;
• (f) disconnecting said first and second differential inputs from said common voltage source;
• (g) reconnecting said first and second differential inputs to said input source;
• (h) setting said variable gain to an application value;
• and
• (i) applying said adjusted bias current to cancel said output offset voltage.

An apparatus for canceling offset in an open loop differential amplifier having a variable gain comprising:

• an offset detector operative to connect first and second differential inputs of said amplifier to a common source, maximize said variable gain and detect offset voltage imparted by said amplifier alone and further operative to determine an appropriate bias current in said amplifier to cancel said detected offset voltage;
• and
• an offset compensator operative to return said variable gain to an application based value and apply said appropriate bias current to said amplifier to cancel said offset voltage
• wherein said amplifier is configured to function in alternating operational and non-operational phases, wherein said offset detector is configured to operate during said non-operational phase and said offset compensator is configured to operate during said operational phase.

An apparatus for canceling offset in an open loop differential amplifier comprising:

• means for detecting an offset voltage in first and second differential output signals of said amplifier, said offset voltage added by said amplifier, and determining an appropriate bias current in said amplifier to cancel said detected offset voltage;
• means for reducing residual offset;
• and
• means for applying said appropriate bias current to said amplifier to cancel said offset voltage
• wherein said amplifier is configured to function in alternating operational and non-operational phases, wherein said means for detecting an offset voltage is configured to operate during said non-operational phase and said means for applying said appropriate bias current is configured to operate during said operational phase.