System and method for signal level detection

1. An electronic signal level detection system comprising:

a comparison circuit having a first input to receive an analog input signal having a variable voltage, the comparison circuit comparing the input signal voltage to a threshold and supplying a comparator signal at an output for input signal voltages exceeding the threshold;

a detector having an input to receive the comparator signal and an output to supply detection signals responsive to receiving comparator signals in a periodic first time frame;

a counter having an input to receive the detection signals and an output to supply a count in a periodic second time frame following the first time frame;

a digital-to-analog converter (DAC) having an input to receive the count and having an output to supply a threshold voltage, for adjusting the threshold and creating a metric representative of the difference between the input signal voltage and the threshold in response to the count;

wherein the counter increments the count in response to receiving a detection signal in the first time frame, and decrements the count in response to not receiving a detection signal in the first time frame; and,

wherein the detector is a detection register setting a detection register output to a first value in response to receiving a comparator signal, and setting the detection register output to a second value, different from the first value, in response to not receiving a comparator signal.

2. The system of claim 1 wherein the comparison circuit includes:

a summing circuit having an input to accept the input signal voltage, an input connected to accept the threshold voltage, and an output to supply a sum voltage; and,

a comparator having a first input to accept the sum voltage,

a second input connected to a fixed comparator input voltage, and an output to supply the comparator signal.

3. The system of claim 2 wherein the comparator compares an input signal voltage having a positive voltage with respect to an average input signal voltage, to a high voltage threshold in the first time frame, and compares a variable negative voltage with respect to the average, to the low voltage threshold in a periodic third time frame following the second time frame;

wherein the detection register sets a positive detection register output to the first value in response to receiving comparator signals in the first time frame, and sets a negative detection register output to the first value in response to receiving comparator signals in the third time frame; and,

wherein the counter supplies a positive counter value in the second time frame and supplies a negative counter value in a periodic fourth time frame following the third time frame.

4. The system of claim 3 wherein the DAC converts the positive counter value to a positive offset voltage in the first time frame, converts the negative counter value to a negative offset voltage in the third time frame, and supplies an inverted negative offset voltage; and,

wherein the summing circuit sums the input signal voltage with the positive offset voltage in the first frame, and sums the input signal voltage with the inverted negative offset voltage in the third time frame.

5. The system of claim 4 further comprising:

an averaging circuit having inputs to accept the positive and negative counter values, and supplying an average input signal voltage measurement at an output, determined by summing the positive counter value with the negative counter value.

6. The system of claim 1 wherein the comparison circuit is a comparator having a first input to accept the input signal voltage, a second input to accept the threshold voltage, and an output to supply the comparator signal.

7. The system of claim 1 further comprising:

a loss-of-signal circuit having an input connected to the counter to accept the count, and having an output to supply a message indicating the absence of the input signal in response to reading a count less than a low limit, and a message determining the presence of the input signal in response to reading a count greater than a high limit.

8. The system of claim 1 further comprising:

a variable gain amplifier having an input to accept a signal, a control input connected to receive the count, and an output to the comparison circuit to supply the input signal voltage, the amplifier adjusting the gain in response to the count.

9. The system of claim 1 wherein the counter supplies an n-bit counter value in response to the detection signals; and,

wherein the DAC accepts the in most significant bits of the counter value, where m is less than or equal to n.

10. An electronic signal level detection system comprising:

a comparison circuit having a first input to receive an analog input signal having a variable voltage, the comparison circuit comparing the input signal voltage to a threshold and supplying a comparator signal at an output for input signal voltages exceeding the threshold;

a detector having an input to receive the comparator signal and an output to supply detection signals responsive to receiving comparator signals in a periodic first time frame;

a counter having an input to receive the detection signals and an output to supply a count in a periodic second time frame following the first time frame;

a digital-to-analog converter (DAC) having an input to receive the count and having an output to supply a threshold voltage, for adjusting the threshold and creating a metric representative of the difference between the input signal voltage and the threshold in response to the count; and,

a loss-of-signal circuit having an input connected to the counter to accept the count, and having an output to supply a message indicating the absence of the input signal in response to reading a count less than a low limit, and a message determining the presence of the input signal in response to reading a count greater than a high limit.