Physics and Engineering of Radiation Detection

8.7. Analog to Digital Conversion 503

−

+

Clock

Counter

Converter

Analog

Digital

to

Vin

Comparator

Up/Down

Output

Figure 8.7.5: Schematic of an 8-bit tracking ADC. The

counter starts counting up (down) whenever the compara-

tor’s output is high (low). Shift register is not required in

such a design.

Vin

Time

Figure 8.7.6: Conversions in a tracking

ADC. The counter never gets reset once

it starts counting unless the analog input

drops to zero.

3.The capacitor is disconnected from the pulse stretcher circuit.

4.A current source is connected to the capacitor, which starts discharging it

linearly.

5.At the same time, a counter is started to count the number of clock pulses it

takes the voltage on the capacitor to reach the baseline voltage. If the source

provides a constant currentisthroughout the discharge then it will take time

td=Vin

C

is

(8.7.2)