A/D reference level adjustment circuit to maintain optimum dynamic range at the A/D

A circuit for providing a reference voltage to an analog-to-digital (A/D) converter which provides I and Q digital outputs, the circuit comprising:

• a sensor connected to an A/D converter for indicating when I and Q outputs from the A/D converter are either a plus or a minus full scale voltage;
• a logic unit responsive to said sensor and connected to an accumulator, said logic unit for incrementing said accumulator by a first amount when either the I or the Q output from the A/D converter is either a plus or a minus full scale voltage and for decrementing said accumulator by a second amount when neither the I nor the Q output is either a plus or a minus full scale voltage;
• a digital-to-analog (D/A) converter which provides a reference voltage for the A/D converter;
• and
• a counter responsive to said accumulator for changing a count of said counter when said accumulator over or under flows, and for providing the signals to said D/A converter to change the reference voltage when there is a change in a predetermined number of most significant bits of the count in said counter,
• whereby signals to said D/A converter from said counter increase the reference voltage when either the I or the Q output from the A/D converter is either a plus or a minus full scale voltage and which decrease the reference voltage when neither the I nor the Q output is either a plus or a minus full scale voltage.

A method of controlling a reference voltage for an analog-to-digital (A/D) converter which provides I and Q digital outputs, the method comprising the steps of:

• (a) sensing when I and Q outputs from an A/D converter are at least a desired voltage;
• (b) forming signals for increasing the reference voltage when either the I or the Q output from the A/D converter is at least the desired voltage and decreasing the reference voltage when neither the I nor the Q output is at least the desired voltage;
• and
• (c) providing the formed signals to a D/A converter which provides a reference voltage for the A/D converter.

A method of controlling a reference voltage for an analog-to-digital (A/D) converter which provides I and Q digital outputs, the method comprising the steps of:

• (a) sensing the I output from an A/D converter using a first sensing means to determine the voltage while simultaneously sensing the Q output from the A/D converter using a second sensing means to determine the voltage;
• (b) comparing the I and the Q outputs against a desired voltage using a logic means;
• (c) accumulating the output from the logic means;
• (d) forming a signal for increasing the reference voltage when either the I or the Q output from the A/D converter is at least the desired voltage and decreasing the reference voltage when neither the I nor the Q output is at least the desired voltage;
• and
• (e) providing the formed signal to a D/A converter which provides a reference voltage to the A/D converter.