Inexpensive Fast 10 Bit Serial Output A/D

Everytime a pulse is applied to the convert command input, Q1 resets the 1000 pF capacitor to 0V. This resetting action take 200 ns of the falling edge of the convert command pulse, the capacitor begins to charge linearly. In precisely 10 microsecond, it charges to 2.5V. The 10 microseconds ramp is applied to the LT1016's positive input. The LT1016 compares the ramp to Ex, the unknown, at its negative input. For a 0V - 2.5 V range, Ex is applied to the 2.5 k ohm resistor. From a 0V - 10 V range, the 2.5 k ohm resistor is grounded and Ex is applied to the 7.5k ohm resistor. Output of the LT1016 is a pulse whose width is directly dependent on the value of Ex. This pulse width is used to gate a 100 MHz clock. The 100 MHz clock pulse bursts that appear at the output are proportional to Ex. For a 0V - 10 V input, 1024 pulses appear at full- scale, 512 at 5.00 V, etc.

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