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1、LPRO Rubidum Oscillator USERS GUIDE and INTEGRATION GUIDELINES S/O/102502D LPRO Rubidium Oscillator for Time 5,457,430; 5,489,821; 5,656,189; 5,721,514 and patents pending. Trademarks X72 is a registered trademark of Datum. Other trademarked terms may appear in this document as well. They are marked

2、 on first usage. Warranty Datum provides a 2 year warranty on this product. i RadioFans.CN 收音机爱 好者资料库 LPRO Rubidum Oscillator Table of Contents REFERENCES Additional Documentation. iv SECTION ONE - Introduction and Specifications 1.0 Description.1 1.1 Typical Applications . 1 1.2 LPRO Specifications

3、 . 3 SECTION TWO - Installation and Operation 2.1 Theory of Operation . 6 2.2 Installation. 7 2.2.1 Site Selection . 7 2.2.2 Cabling . 7 2.3 Turn-on Procedure . 7 2.4 Frequency Adjustment Procedure. 8 2.5 Maintenance. 10 SECTION THREE - Design Integration Considerations 3.1 Mechanical Issues . 11 3.

4、1.1 Recommended Mating Connectors. 11 3.1.2 Circuit Card Mating Recommendations . 11 3.1.3 Mounting Guidelines . 11 3.2 Thermal Considerations. 11 3.2.1 Use of Thermal Tape. 11 3.2.2 Test Heat Sink . 12 3.2.3 Impact of Ext. Ambient Air Temp. on Unit Operation . 12 3.2.4 Unit Operating Temperature Ra

5、nge . 13 3.2.5 Frequency Offset from Water Condensation . 14 3.3 External Interfaces and Grounding. 15 3.4 Electrical Interface. 17 3.4.1 LPRO rf Output . 17 3.4.1.1 Conversion of 10 MHz sine to 10 MHz TTL . 17 3.4.1.1.1 ac-coupled, CMOS Gate . 17 3.4.1.1.2 ECL-TTL Level Shifter . 17 3.4.1.1.3 Use o

6、f a LT1016 Comparator . 19 3.4.1.2 Output Impedance versus Frequency. 20 3.4.1.3 ac-coupled rf Load. 20 3.4.2 Transformer-coupled rf Load. 21 (continued) ii RadioFans.CN 收音机爱 好者资料库 LPRO Rubidum Oscillator Table of Contents (continued) 3.4.3 Isolation of Chassis. 21 3.4.4 Shorted Output, Open Output

7、Cases . 21 3.5 Built-in Test Equipment (BITE) Signal. 21 3.5.1 Recommended Customer Interface to BITE . 21 3.6 C-Field Frequency Control. 22 3.6.1 1E-9 Internal or External Control . 22 3.6.2 Time Response of External C-field Control . 22 3.6.3 Temperature Compensation of Frequency Using Ext. C-fiel

8、d Control . 22 3.7 EMI Considerations. 23 3.7.1 Outer Mu-Metal Cover . 23 3.8 LPRO Susceptibility to Input Noise . 23 3.9 LPRO Maintenance. 24 3.9.1 LPRO Design Goal. 24 APPENDIX A J1 and Board Connector Guidelines and Datasheets. 25 LIST OF ILLUSTRATIONS Figure 1-1. LPRO Rubidium Oscillator . 1 Fig

9、ure 1-2. LPRO Outline Drawing . 2 Figure 1-3. Total Unit Power Dissipation, Typical (free convection) . 5 Figure 1-4. Representative LPRO f/f versus Temperature. 5 Figure 2-1. LPRO Rb Control Loop Block Diagram . 6 Figure 2-2. Suggested Connections for LPRO, Initial Turn-on. 7 Figure 2-3. Top View o

10、f LPRO Showing C-Field Adjustment Access Hole. 9 Figure 3-1. Interface Circuitry of LPRO Connector J1. 16 Figure 3-2. Sine-to-TTL Conversion Using C-MOS Logic, Recommended Approach. 18 Figure 3-3. Sine-to-TTL Conversion, Using C-MOS Logic, Self-Bias Approach. 23 Figure 3-4. Sine-to-TTL Conversion Ci

11、rcuit, Using Positive ECL Converter. 23 Figure 3-5. Sine-to-TTL Conversion Circuit Using a High Speed Comparator. 23 Figure 3-6. rf Output Impedance Versus Frequency. 24 Figure 3-7. rf Output Impedance Versus Frequency. 24 Figure A-1. Suggested Mating to Circuit Card Assembly. 33 LIST OF TABLES Tabl

12、e 1a. J1 Connector Interface . 2 Table 1b. Mating Connector Options . 2 Table 3-1. Phase Noise, Sine-to-TTL Circuits. 18 Section Three (continued) iii LPRO Rubidum Oscillator References 1. NIST Technical Note 1337, “Characterization of Clocks and Oscillators,” Sullivan, Allan, Howe, Walls, Editors,

13、March 1990. 3. “Frequency Stability: Fundamentals and Measurement,” V. Droupa, Editor, IEEE Press, 1983 4. “General Considerations in the Metrology of the Environmental Sensitivities of Standard Frequency Generators,” IEEE Frequency Control Symposium, 1992, pp 816-830. 5. NIST Technical Note 1297, “

14、Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results,” 1994 Edition, B. Taylor and C. Kuyalt. 6. “The Use of Statistics for Specifying Commercial Atomic Frequency Standards,” DeWatts etal, 1996, Frequency Control Symposium. iv 1 LPRO Rubidum Oscillator LPRO Users Guid

15、e DF 4 WDSFL;F 5 EEF 6 PLDFKDF 7 WPLEPEL 8 DFL;DF 9 WDSFL;F 10 EEF 9 WDSFL;F 9 WDSFL;F 9 WDSFL;F SDPSDC SDC SDDFS ERFF ERR ERAQ C-FIELD ADJUSTMENT ACCESS HOLE The second method of adjustment is electronic, using the External C-field control signal at pin J1-7. The unit is set to a nominal 2.5Vdc sig

16、nal at the factory through this pin. Increasing the voltage will increase the output frequency. The allowable correction range is 0Vdc to +5Vdc, al- though positive voltages up to 36Vdc can be applied without causing damage or latch-up. Operating with negative voltages at J1-7 is not recommended, as

17、 latchup of the internal op amp can result when a voltage more negative than -8 Vdc is applied. Using an external counter suitable for the task (this operation requires a measurement accu- racy that exceeds most counters), adjust the unit so that the output rf frequency is 10,000,000.000 Hz. NOTE: i

18、f the LPROs output signal frequency must be changed, this can be done electronically by connecting the positive voltage of a low output impedance voltage reference to J1-7 and its return to J1-2 (or J1-4, chassis ground) The recommended output impedance is 1 k ohms for the reference voltage, althoug

19、h a higher output impedance can be tolerated (the input impedance for this signal is approximately 151 k ohms). Increasing the positive voltage provides an increasingly positive frequency offset. The correction voltage range is 0 to +5Vdc, where no external frequency offset correction is nominally a

20、t 2.5 Vdc. LPRO Installation the resonator heater power, the lamp heater power, and the electronics power. The resonator heater power is determined primarily by the resonator control temperature of +78C, the baseplate temperature, and the 15.3 C/W thermal resistance from the resonator to baseplate.

21、The lamp heater power is determined primarily by the lamp control tempera- ture of +110C, the baseplate temperature, and the 53 C/W thermal resistance from the lamp to baseplate. The electronics power reflects nearly a fixed electronic current that is independent of input voltage due to the units in

22、ternal 17 V regulator and is roughly independent of of baseplate tempera- ture. The heater powers are roughly independent of input voltage. An equation to approximate quiescent input power consumption for the unit is: PQ VPS * (280 mA) + (78C - TBP) / (15.3C/W) + (110C - TBP) / (53C/W) electronics p

23、wrresn htr pwr lamp htr pwr This equation is only an approximation, since it ignores effects like internal self-heating, power losses from the heater reverse protection diode, and power losses from the heater current sense resistors. The LPRO maximum baseplate temperature described in the specificat

24、ions was based on a model where the unit was covered on five sides with one inch foam to simulate free convection in air as the heat sink/baseplate was exposed to forced air. The maximum operating baseplate temperature will be lower by several degrees C if the external air is hotter than the basepla

25、te mounting. An example is a situation where the baseplate is being cooled by a thermoelectric cooler, but is exposed to nearby heat-producing equipment. If there is air flow over the units top cover, the LPROs maximum operating baseplate tem- perature will increase by 1 or 2 degrees C and its power

26、 consumption at a given baseplate tempera- ture will also increase by a few tens of milliwatts. LPRO Design Integration Considerations 13 LPRO Users Guide a 6C rise occurs thirty minutes to one hours after turn-on. 3. Temperature range from 70C to 75C baseplate. This is the emergency operating tem-

27、perature range that maintains lock (but has no guaranteed warm-up period). The upper limitation is derived by staying under the upper operating temperature of the crystal as well as avoiding the loss of thermal control of the resonator. This condition is not recommended for long operating period bec

28、ause once heater control is lost, the unit may take on a frequency offset (typically parts in 10-11) that will be present for many days of operation while the unit returns to equilibrium. Also, DATUM part derating guidelines are exceeded under this condition, although the component manufacturers max

29、imum part rating guidelines are not, provided the baseplate temperature is kept below 75C. LPRO Design Integration Considerations 14 LPRO Users Guide 1. 1000 pF PI feedthrough capacitor/ferrite for power/power return and monitor signals 2. 470 pF PI feedthrough capacitor/ferrite for the rf and dc is

30、olated rf return signals, and . . . 3. shorting pin for the two chassis ground pins (either one of which is the recommended rf return pin). LPRO Design Integration Considerations 16 LPRO Users Guide these transients are minimized if temperature ramp rates are limited. Changing less than +2C/minute b

31、aseplate temperature should result in negligible transients from mismatches. There are issues with changing the C-field current in atomic frequency standards for the impact on aging and other parameters, but this is more of an issue for expensive laboratory fre- quency standards with significantly t

32、ighter aging specifications than a LPRO unit. LPRO Design Integration Considerations 23 LPRO Users Guide & Integration Guidelines 06-09-2000 S/O/102502D 3.7 EMI CONSIDERATIONS 3.7.1 Outer Mu-Metal Cover The resonator packages of rubidium frequency standards have significant frequency offsets due to

33、external magnetic fields. For this reason, it is customary to use a double mu-metal shield for the resonator housing in order to meet the magnetic susceptibility specification for the unit of parts in 10-11/gauss. The LPRO was designed so that the unit cover forms the second, outer magnetic shield.

34、The cover is made of mu-metal, with overlapping edges that minimize problems with fringing fields. The advantage of this approach is the resulting magnetic shielding of the electronics outside of the resonator package. 3.8 LPRO Susceptibility to Input Noise When a user has an application where the o

35、utput spectrum phase noise and spur integrity is crucial, the LPRO must be provided with comparatively clean source of dc power (free of spurious current or voltage noise). Connecting fans and other electromechanical devices to the dc supply powering the LPRO can result in degraded phase noise and s

36、pur performance. This is because motors with brushes can create a wide spectrum of noise. The frequency spectrum of the spurs will vary largely with the motors speed and load conditions. The Rb atomic frequency source uses a modulation/demodulation lock-in amplifier scheme with a modulation frequency of 152 Hz. Inherent in this approach is sensitivity to noise at multiples of t