Wether in geodesics, in security systems, production controls or just on the golf corse - the measuring of distances with lasers or laserscanners is well established nowadays.
The time - namely the time light needs to pass the needed distance - is the value to be determined. This sounds so simple, but it isn't - because the velocity of light is very, very high - it's 2.99792*10 8 m/s. In consequence one has to deal with very small times. In only one microsecond the passes 300 meters. A high resolution in place therefore demands highest resolution in time.
For pratical reasons the reflection mode is used. Tranceiver and receiver are placed in one device. For the distance to be measured we find d=c*t/2 with c=velocity of light. So if we take a distance of 1 kilometer, the time of flight will be 6.7µs. If the resolution has to 1cm we already need a time resolution of 67ps. TDC-GPX driven in M-Mode shows a peak-to-peak resolution very close to this. The resolution can be further improved by averaging without seeing any systematic errors from the TDC.
Laser Distance Meter - TDC Advantages
Advantages of the TDC used in a Laser Distance Meter Application
Direct conversion of time to digital values
Highest resolution down to 10ps (70ps peak-to-peak)
Multichannel - TDC-GP1 and TDC-GP2 have two stop channels, TDC-GPX up to 8 channels
Multihit-capability - TDC-GP1 and TDC-GP2 can handle 4 Stops, TDC-GPX up to 32 Hits
High Update rates - TDC-GPX can measure with 200MHz peak rate
Direct pulse width measurement - TDC-GPX can directly measure the pulse width down to 1.5ns
Space savings - Single Chip-solution in a small QFN32, TQFP44 or TQFP100 package
Industrial operating range from -40°C to +120°C .
Battery applications - for handheld devices a low current consumption is essential. Discover the TDC-GP2 - it's perfect for this! When you work in measuring range 2 with only one measurement plus calibration per second, the current consumption will be only 3uA for a 5V supply (Note: nearly the comlete consumption is delivered to the calibration clock)
TDC Laster Distance Meter Measuring Principle
TDC Laster Distance Meter Application Notes
Application Note No. 1
Reflections with a Double Pulse Resolution of 15ns.
How is the supply current of the GP1 calculated?
In measurement rage 1 the supply current for the GP1 is strongly dependent on the sampling rate and the reference clock frequency. It will be shown on an example:
The measurement rate may be 100 samples per second with a 4MHz reference clock. For the current consumption we find: max. measurement time = 3,8µs (≡ 570m) 100*3,8µs=380µs actice measurement time supply current TDC-core = 25mA*380µs/1s=9,6µA (1) with clibration the ALU is active for 100*2µs = 200µs supply current ALU = 5mA*200µs/1s=1µA (2) supply current reference clock 90µA/MHz*4MHz = 360µA(3) supply current data I/O = 2mA/MB*s*400B/s=1µA (4) The total supply current of the GP1 is about 372µA...Continue to View Complete Application Note
