TDC-GP21 datasheet(72/91 Pages) AMSCO

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TDC-GP21

acam messelectronic gmbh - Friedrich-List-Str.4 - 76297 Stutensee - Germany - www.acam.de

5-1

Details and Special Functions

5.1

Oscillator

The TDC-GP21 uses up to 2 clock signals depending on the operating mode:



High-speed clock, typically 4 MHz, for calibration and as a predivider for the TDC

measuring unit in measurement mode 2 and for the EEPROM



32 kHz clock signal used for internal timer functions.

5.1.1

High-Speed Oscillator

Generally, the TDC-GP21 needs a high-speed clock for calibration. The recommend value is

4 MHz, the possible range is 2 to 8 MHz (2 to 6 MHz in QUAD_RES mode). When running

in measurement mode 2 the TDC-GP21 needs the high-speed clock signal also as a part of

the time measuring unit. Finally the operations need the high speed clock, too.

The oscillator takes an average current of 200 µA when running all the time. But as it is

needed only during the time measurement, the TDC-GP21 has the capability to control the

on-time by itself. The settings are done with parameter START_CLKHS. With

START_CLKHS > 1 the oscillator is switched on after sending opcodes Start_TOF,

Start_TOF_Restart, Start_Temp and Start_Temp_Restart for the duration of the

measurement. A delay between starting the oscillator and starting the measurement

guarantees sufficient time for the oscillation to settle at full amplitude.

Note:

It is strongly recommended to use a ceramic oscillator. Exactly because a quartz needs

much longer to settle than a ceramic oscillator. This costs a lot current, but using a

quartz oscillator has no advantage.

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TDC-GP21 Datasheet(PDF) 72 Page - ams AG