Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 174 (2017 ) 1257 1261 13th Global Congress on Manufacturing and Management, GCMM 2016 Research on the High resolution precision time-interval measurement methods Jun Zhao*, Zhiliang Zhao, Li Fu 92493 units, Huludao City, Liaoning Province,China Abstract High-precision and high-resolution time intervals are needed to improve high-precision measurement in time-frequency measurement system. The paper introduces the measurement technique and design of 1 ns time interval measurement, and analyzes the realization of analog interpolation and high-resolution precision time interval measurement. Research and analysis show that the analog interpolation method can not only meet the high-precision and high-resolution time difference measurement, but also improve the 1 ns time interval measurement. 2017 2016 The Authors. Published by Elsevier by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 13th Global Congress on Manufacturing and Management. Peer-review under responsibility of the organizing committee of the 13th Global Congress on Manufacturing and Management Keywords: metrology; High resolution; precision measurement; time-interval; simulate interpolation 1. Introduction Precise Time and Time Intervals (PTTI) are very important for all armed force. Now there are many military actions must be dependent on PTTI.In order to meet high precision index requirement of the PTTI measurement system, it requires a high precision, high resolution intervals of time counter. Because of universal time-interval counter can t meet the requirement of measurement, so it needs to use interpolation to realize high precision and high resolution time difference measurement to satisfy the 1ns time-interval measurement. These are two interpolation techniques in the time-interval measurement, one is the digital cursor interpolation; the other is analog interpolation. Digital cursor interpolation is applied to higher precision time interval counter, such as HP5370A time interval counter [1]. It makes the measured resolution at 20 ps (single measurement). But it is difficult to design three digital interpolation triggering phase-locked oscillators. In this paper, the measurement resolution is 1 * Corresponding author. Tel.: +86-1399-8944-000. E-mail address: navy2002cn@126.com 1877-7058 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 13th Global Congress on Manufacturing and Management doi:10.1016/j.proeng.2017.01.298
1258 Jun Zhao et al. / Procedia Engineering 174 ( 2017 ) 1257 1261 nanosecond, the measured resolution can reach 100 picoseconds from increasing the interpolation clock frequency of 80 MHz to meet the measurement system 1 ns time interval measurement requirements [2]. 2. Time-interval measurement and simulate interpolation technique In the measurement of time interval, quantizing error limits the measured resolution improvement. Measuring time-interval is counting reference clock pulse in a period. Therefore, there is always ±1counting error [3], timeinterval counter quantizing error is ±1 reference clock error. The 100 MHz reference clock counter measures a resolution of 10 ns. But depend on the 1 ns resolution measurement, the clock frequency will improve to 1 GHz above, which the problems such as electromagnetic interference and circuitry problems will be hard to solve properly, so it s not realistic to improve test resolution by unlimited increase clock frequency. Interpolation is an effective method to reduce quantization error. Simulate interpolation is a method which base on time-voltage-digital [4] transform. The paper use simulate interpolation counter to realize high precision and high resolution timeinterval measurement. Time-digital converter is made of input port (Start/Stop and Clock signal), input wave number calibration channel, time-voltage-digital converter cell and microchip. Start/Stop signal reforming trigger Start/Sto -to- Clock Pulse width-voltage Pulse conversion Sample and hold Clock signal Time-voltage-digital conversion microchip Fig. 1 Time-digital conversion unit chart. Start Stop Start-to-Clock Stop-to-Clock tst Precision capacitance charge-discharge V c V d Sample and hold Quick charge tsp Fig. 2. Simulate interpolation method schematic diagram. Simulate interpolation's principle is shown as figure 2. Use a constant source for fast charge, the capacitance which in the pulse width-voltage width conversion unit's voltage is a constant. Before the Start-to-Clock pulse leading edge coming, it begins to discharge in a constant current, when it comes to Start-to-Clock pulse lag edge, discharge ends. So we can find a connection between the pulse and electrical capacitance. It can calculate the Startto-Clock pulse width value tst, by measuring voltage, so we can get the tsp value in the same way. t VT c 0 st, d 0 tsp V0 V0 VT (1)
Jun Zhao et al. / Procedia Engineering 174 ( 2017 ) 1257 1261 1259 V0 is voltage resolution, Time-digital conversion resolution, it's electrical capacitance complete charge and discharge V0 's time. Fig. 3. Interpolation counting method s timing diagram. Figure 3 is the simulate interpolation counting method s timing diagram. The part between the STARTA rising edge and the STOPA rising edge is to be measured which called time interval T, STARTA XOR STOPA can get the main counter computing interval which is the time interval to be measured. Put the time intervals which is less than the main counter s clock cycle before and after the main counting time interval into TDC for precise time quantization, will get the tst and tsp respectively. The main counter clock cycle is Tc, counting results is Nc. time interval is T can be shown by formula (2). T t t N T st sp c c 3. Overall scheme analysis and the implementation technology approach To meet the precision measuring time interval, it must choose high resolution counter, high resolution can be achieved with high accuracy measurement of the 1 ns time interval counter. 1 ns time interval counter overall scheme shown as figure 4, it composed by two parts which are the main counter and simulation interpolation. It also use rapid ECL circuit and FPGA. Enabling pulse 40M clock signal Slope Sample-andhold conversion Multicycle synchronization time main counter Controler Gate control Enabling pulse interpolation Closed pulse interpolation Main counter computing Time interval computing (2) Closed pulses Slope Sampleand-hold conversion Fig. 4. Time interval counter overall scheme.
1260 Jun Zhao et al. / Procedia Engineering 174 ( 2017 ) 1257 1261 1ns resolution time interval measurement use interpolation. Clock frequency chooses 40MHz. It base on two consideration, on one hand if choose low clock frequency, two clock pulse interval is big, in the condition of AD converter digit is fixed, 1 bit time interval is big, it can t recognize small time interval, it can t improve resolution; On the other hand if choose high clock frequency, the circuit will be too complicated. Fig. 5. Time interval logic generate circuit diagram. Quick time interval logic generate circuit diagram is shown as figure 5, it use ECL circuit, which composed by three series connection trigger and a XOR circuit controller generate time interval to be measurement Start-to-Clock. The simulation interpolation measurement usually begins to measure after 1 clock. In the paper, for guaranteeing measurement accuracy, it measures after the opening and closing, when the reference clock frequency is 40MHz, clock cycle T0 = 25ns, When the time interval T is too small, the current switch rate, charge beginning and end point later time interval-voltage width conversion will change extremely. Therefore, set Start-to-Clock pulse width for T0+T, that is 25-50ns, it will help to eliminate dead zone and zero area nonlinear in the beginning and ends. It s working chart shown as figure 5. Q (XOR output) output port is Start-to-Clock. Digital interpolation layout schematic diagram is shown as figure 6. Before it is triggered, audion Q2 is cut-off, precision integral capacitance Ci is charging through current source I2. It makes the capacitance maintaining a constant voltage. In figure 6, when XOR Q port s output time interval impulse Start-to-Clock leading edge coming, Q2 breakover, capacitance Ci is connecting source I1, it begins to discharge as a constant current (I1-I2), when the Start-to-Clock s lagging edge coming, Q2 is cut-off again, discharge ends. At this time, the voltage of the capacitance and the time interval pulse width has a simple linear relation.
Jun Zhao et al. / Procedia Engineering 174 ( 2017 ) 1257 1261 1261 Fig. 6. Digital interpolation layout schematic diagram. After discharge, voltage Ci maintains at Ch for a short time after amplification and sample-and-hold. It s sent to a 12 bit converter, the microprocessor can calculate the result. So we can get the high resolution time interval. When we use the 40MHz clock as the reference signal, every two clock pulse interval is 25 ns. Due to the AD converter is 12 bit, 212 = 4096 bit, 25 ns time interval take up two-thirds of 4096 bit, namely 2730 bit, this means that this time-digital converter theoretical resolution is 25000 ps / 2730 9ps/bit. The measuring error is less than 250 ps. It s satisfy the system s error 500 ps. 4. Conclusion PTTI measurement is widely used in communication, electron war, satellite and navigation location and so on. For example, the improving of radar distance-measuring precision depends on the improving of emission and echo pulse time interval precision. Radar PRI's high precision improving is a question of time interval measuring. Multistation location precision improves depend on time interval measuring. Time difference measuring belongs to time interval measuring category. Therefore, precision time interval measuring research is very important. Reference [1] hp 5370B Universal time Interval Counter Operating and Service Manual, 3(1984). [2] Y Wang "High precision time-interval measurement and analysis system" technical report, Unit 89 in 92493 of PLA. (2008). [3] T Gu, H J Wang, Y B Xi, etc. Electronics measuring principle, Beijing: mechanical industry press, (2004) 148-165. [4] A High Resolution Time-to-Digital Converter Based on Time-to-Voltage Interpolation.