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Time to Digital Converter (TDC) Basics and ICs

digital converter time measurement integrated circuit sensor application measurement technique

This page delves into the fundamentals of time to digital conversion. It provides application notes on popular Time to Digital Converter ICs available from various semiconductor manufacturers. In the realm of digital signal processing and electronics, these converters play a crucial role in recognizing the time interval between two events (such as ‘START’ and ‘STOP’) and measuring time in digital formats.

What is a Time to Digital Converter?

A time to digital converter is a device that transforms a time interval into a measurable digital or binary format.

Common implementations involve a counter that increments or decrements with each clock cycle. To achieve long-term stability, these converters often use a crystal. The counter technique is suitable for coarse measurements. Finer measurement techniques include ramp interpolators, vernier methods, and tapped delay lines.

Hybrid methods offer both long interval measurement and high resolution.

Time to digital converters find wide application in:

  • Flow meters (for water, gas, and heat measurement)
  • Magnetostrictive sensors (for position/level sensing)
  • Time of flight measurements in drones
  • Metering equipment and projectors

Time to Digital Converter from TI

Image Courtesy: Texas Instruments Incorporated

The figure depicts the TDC7200 from TI, which can be utilized as a time to digital converter. This IC essentially functions as a stopwatch, measuring the elapsed time (i.e., Time of Flight or TOF) between a START pulse and up to five STOP pulses.

Time to Digital Converter ICs

The following table highlights key features of time to digital converter ICs from prominent semiconductor manufacturers.

IC ManufacturersPart NumberDescription of features
Texas Instruments IncorporatedTDC7200• Measurement Range: Mode-1: 12 ns to 500 ns and Mode-2: 250 ns to 8 ms
• Data output (DOUT) format: SPI
• Data In (DIN) pin is provided. This pin is driven by SPI master by transmitting command and data byte to configure the IC.
• Standard deviation : 35 ps
• Resolution : 55 ps
• Supply : 2V to 3.6V
Maxim IntegratedMAX35101, MAX35102• The IC MAX35101 offers time measurement accuracy of about 20ps, measurement range upto 8 ms, 4 wire SPI interface etc.
• The IC MAX35102 is similar to MAX35101 but with reduced features. Moreover it does not house RTC (real time clock).
Integrated Device Technology, Inc.ClockMatrix TM TDC• This family based devices can be used for speeds upto 100 Gbps interface.
• They are used for various functions such as clock generation, jitter attenuation, frequency translation and phase alignment.
• The common programmable interfaces supported are SPI or OTP and I2C.
ams AGAS6500, AS6501, TDC-GPX, TDC-GPX2• AS56500 time to digital converter IC supports 4 stop channels with 20ns pulse to pulse spacing.
• It offers maximum speed of about 1.5 MSPS via SPI interface.
• It offers unlimited measuring range from 0 to 16 seconds.
• Resolution of about 20 ps can be achieved.
• Check https://ams.com/ for more information on other time to digital converter ICs offered by AMS.
LeCroy CorporationMTD135, MTD133B• They are 8-Channel, Multi-hit Time-to-Digital Converter ICs manufactured by LeCroy Corporation.