29-11-2012, 04:18 PM
Analog to Digital Converters
[attachment=41705]
Conversion Methods
Ladder Comparison
Successive Approximation
Slope Integration
Flash Comparison
Single slope integration
Charge a capacitor at constant current
Count clock ticks
Stop when the capacitor voltage matches the input
Cannot achieve high resolution
Capacitor and/or comparator
Flash Comparison
If N is the number of bits in the output word….
Then 2N comparators will be required.
With modern microelectronics this is quite possible, but will be expensive.
Resolution Example
Temperature range of 0 K to 300 K to be linearly converted to a voltage signal of 0 to 2.5 V, then digitized with an 8-bit A/D converter
Conversion Time
Time required to acquire a sample of the analog signal and determine the numerical representation.
Sets the upper limit on the sampling frequency.
For the A/D on the BalloonSat board, TC ≈ 32 μs,
So the sampling rate cannot exceed about 30,000 samples per second (neglecting program overhead)
[attachment=41705]
Conversion Methods
Ladder Comparison
Successive Approximation
Slope Integration
Flash Comparison
Single slope integration
Charge a capacitor at constant current
Count clock ticks
Stop when the capacitor voltage matches the input
Cannot achieve high resolution
Capacitor and/or comparator
Flash Comparison
If N is the number of bits in the output word….
Then 2N comparators will be required.
With modern microelectronics this is quite possible, but will be expensive.
Resolution Example
Temperature range of 0 K to 300 K to be linearly converted to a voltage signal of 0 to 2.5 V, then digitized with an 8-bit A/D converter
Conversion Time
Time required to acquire a sample of the analog signal and determine the numerical representation.
Sets the upper limit on the sampling frequency.
For the A/D on the BalloonSat board, TC ≈ 32 μs,
So the sampling rate cannot exceed about 30,000 samples per second (neglecting program overhead)