Adaptive analog-to-digital converter

An analog-to-digital (A/D) converter system having an input terminal responsive to an input amplitude varying analog signal for producing a digital output signal, comprising in combination:

• an A/D converter responsive to an internal amplitude varying analog signal for producing a succession of digital output words comprising said digital output signal, said succession of digital output words having a succession of values as a function of time representing respective successive values of said internal analog signal as a function of time and responsive to said internal analog signal being above a preselected upper limit for producing a digital word having a maximum value and responsive to said internal analog signal being below a preselected lower limit for producing a digital word having a minimum value;
• means providing gain controllable signal amplification and means providing direct current (DC) offset coupled between said input terminal and said A/D converter for providing said internal analog signal to said A/D converter;
• first means coupled to said means providing gain controllable signal amplification and responsive to the output words produced by said converter for producing a first control signal when both the number of said maximum value digital words is in excess of a first given fraction of said succession of digital words and the number of said minimum value digital words is in excess of a second given fraction of said succession of digital words, said first means including means for applying said first control signal to said means providing gain controllable signal application for decreasing the gain in said means providing gain controllable signal amplification, said first means being responsive to the output words produced by said converter for producing a second control signal when both the number of said maximum value digital words is less than a third given fraction of said succession of digital words and the number of said minimum value digital words is less than a fourth given fraction of said succession of digital words, said first means including means for applying said second control signal to said means providing gain controllable signal amplification for increasing the gain of said means providing gain controllable signal amplification;
• and
• second means coupled to said means providing DC offset and responsive to the output words produced by said converter for producing a third control signal when both the number of said maximum value digital words is in excess of said first given fraction and the number of minimum value digital words is less than said fourth given fraction, said second means including means for applying said third control signal to said means providing DC offset for decreasing the offset thereof, said second means being responsive to the output words produced by said converter for producing a fourth control signal when both the number of said maximum value digital words is less than said third given fraction and the number of said minimum value digital words is in excess of said second given fraction, said second means including means for applying said fourth control signal to said means for providing DC offset for increasing the offset fhereof.

An arrangement for producing digitized signal samples of analog television signals available in field/frame format said arrangement comprising, in combination:

• a gain-controlled source of said analog television signals having an analog television signal output and having respective input terminals for receiving a gain control signal and a DC baseline control signal;
• analog-to-digital converting means having an input coupled to said analog television signal output of said sorce of analog television signals, and having an output for producing said digitized signal samples of the analog television signals applied thereto;
• counting means, coupled to said output of said analog-to-digital converting means and responsive to said digitized signal samples, for producing digital control signals responsive to the level of said digitized signal samples being outside a predetermined range of values at least a fixed number of times measured over at least a field period;
• means, having an input for receiving said digital control signals, and having an output coupled to one of said inputs of said gain-controlled source of analog signals, for developing said gain control signal in response to said digital control signals to control the gain of said source for at least a succeeding field period;
• means, having an input responsive to said digital control signals and having an output coupled to the other of said inputs of said gain-controlled source of analog signals, for producing said DC baseline control signal to control the DC baseline of said analog signal which is to be digitized during a succeeding measuring period;
• and
• means, coupled to said means for producing said digital control signals, for terminating said produced digital control signals after each successive period of said analog television signals.