FMLD-1 photoreceiving module for laser ranging
The photoreceiving modules of FMLD-1 series based on the high-quality pin InGaAs photodiodes are designed to record a laser emission with the normalized temporal position of rising edge of optical pulses, for measurement a time interval between the СТАРТ (start) probing pulse and the СТОП (stop) pulses, reflected from the targets, and outputting the result of range measurement to the targets in digital binary code.
- Equivalent accuracy up to 0.25 m
- Range measurement up to 30 km
- Built-in time interval meter (ИВИ)
- Monoblock unit of receiving channel of laser rangefinder
- Temporal automatic adjustment of sensitivity up to 30 dB
- Dynamic range of input power of emission up to 70 dB
- Laser pulse width from 5 to 300 ns
- Unidirectional supply
Composion of series
|Name of parameter||FMLD-1-1A||FMLD-1-2B||FMLD-1-1B||FMLD-1-2A|
|Sensitive area, µm||120||300||120||300|
|Equivalent accuracy of range measurement, m *||1||0.25||0.25||1|
|Threshold sensitivity, nW *||50||120||50||120|
*At 1064 nm wavelength, 10 ns pulse width, 50% detection probability, probability of false recording of 5·10-4, a temperature of 23±5°C. The threshold sensitivity is lowered by a factor of 1.5 at 1540 nm wavelength.
Specifications of FMLD series
|Name of parameter||Value|
|Supply voltage, V||12±1 *|
|Spectral range, nm||900...1600|
|Laser pulse width, ns||5...300|
|Operating temperature range, °C||-50...+60|
|Number of detected targets||2 **|
|Pulse repetition rate of synchronization during data reading, MHz, no more than||1|
|Power consumption, W, no more than||2.5|
* Delivery of the module with a voltage of 6±1 V and 25±2 V is possible.
** It is possible to increase a number of the detected targets up to 4.
Composition of FMLD series
The FMLD consists of three main functional units: the photoreceiving module (ФПУ), the secondary power supply (ВИП) and the time-interval meter (ИВИ). The FMLD block-diagram is shown in Fig.
The photoreceiving module (ФПУ) carries out recording of an optical pulse, its normalization by an amplitude and correction of the temporary position of a pulse edge. The photoreceiving module has the fast-response trans-impedance amplifier 1, the additional amplifier stage 2, the threshold module 3 and the circuit of correction of the temporary position of a pulse edge 4.
The secondary power supply is designed based on the transformer PWM converter and provides a voltage required for normal operation of the photoreceiving module and the time-interval meter. The circuity of the secondary power supply provides the possibility of switching off the converter during measurements by a strobe signal (СТРОБ) to eliminate the effect of impulse noise, that is, it allows a considerable reduction of a number of the false responses.
The time-interval meter is designed for conversion of start-stop time-interval into digital code and outputting the measurement results.
If necessary, the protocol of data exchange may be modified.
Operation of FMLD modules
The set-up time of the FMLD in operation after delivery of 12 V voltage is no more than 200 ms. For change-over of the FMLD to mode of range measurement it is necessary to set the logic-1 level on the pin 6 6 of the FMLD connector – the active level of a strobe (СТРОБ). In this case the converter of the secondary power supply is switched off to eliminate effect of impulse noise produced by the pulse-width converter. Coincidentally with switching off the secondary power supply, initialization of the time-interval meter and its change-over in ready mode occur. The minimum time between the positive edge of a strobe (СТРОБ) and the rising edge of a start pulse (СТАРТ) is 100 ns (see the temporal diagrams of operation of the FMLD module – ТИНИЦ). Reading of the time intervals begins with coming of the rising edge of a probe pulse (СТАРТ) and ends with coming of the rising edges of the pulses (СТОП1 and СТОП2) reflected from targets, or when the counters of the time-interval meter exceed the maximum values. When coming the pulses (СТОП1 and СТОП2) to the optical input of the photoreceiving module, the logic-1 level, that signals the presence of the first and second target correspondingly, is set on the output 7 of the FMLD connector. After removal of a strobe (setting of the logic-0 level on the pin 6 of the connector) the FMLD module goes to operation of data transmission. Reading of the measured values of a rage is carried out from the pin 7 within TД after the positive drop on the input 9 (see the temporal diagrams of operation of the FMLD module). The data word has a number of digits of 16 bits and transmitted beginning from low-order digit. The value of low-order digit is 6.25 ns.
After termination of measurements, it is necessary that a strobe (СТРОБ) is kept low for 3 ms, as minimum, for total charging of the buffer capacitors of the secondary power supply.
Note. The FMLD module operates in mode of differential gain control (ВАРУ) for decrease of a sensitivity of the photoreceiving module in near zone (~1000 m). In this case a sensitivity of the photoreceiving module varies in exponential law (see the temporal diagrams of operation of the FMLD module) and has the maximum value in 5…8 µs from the pulse edge (СТАРТ).
Designation of pins of the FMLD module connector
|Number of pin||Designation|
|1||+12 V DC|
|3 (output)||Analog output|
|4||Service (do not use)|
|5||Service (do not use)|
|6 (input)||Strobe (active high)|
|7 (output)||Data transmission|
|8 (output)||TTL output|
|9 (input)||Data synchronization (in pulse edge)|
Temporal parameters of FMLD module
Dimensions of FMLD module
The photoreceiving modules, the secondary power supply, the time-interval meter, etc. may be delivered on request.