基于單片機的英文文獻,溫度控制器設(shè)計

1、 514 IEEE TRANSACTIONS ON ULTRASONICS,FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 42, NO. 4, JULY 1995 POWER SUPPLY I 1 ANALOGUE TO C O W E R OUTPUT L L V ffi ISA BUS DEC0DER I Fig. 4. IAM board. II $ . Fig. 3. IS1 board. will settle their frequencies simultaneously and total adjustment time is shor

2、tened. The ACL uses standard instruments such as laboratory IEEE 488 bus controlled frequency counter and temperature chamber. Any IBM compatible PC with ISA bus can be used as the host computer (Fig. 2. Nonstandard elements of the ACL are a specially designed intelligent serial interface (ISI board

3、 and the intelligent analog multiplexer (IAM board. The IS1 board is placed in one of the PC slots. The IAM board is placed inside the temperature chamber, together with the oscillators. The DOS based ACL software is 250 Kbytes long. The description of the nonstandard ACL elements and the ACL softwa

4、re follows. The Intelligent Serial Interface Board The IS1 board enables communication through a simple asynchronous serial bus between the PC on one side and the IAM and pCTCXOs on the other side (Fig. 2. IS1 is designed as a microprocessor system shown in Fig. 3. The microprocessor 68HC811E2 serve

5、s as a master on the serial bus (the oscillators and the IAM are the slaves. IS1 software (to be described later as a part of the complete ACL software package is placed into a 2KB EEPROM. RAM is used for temporary placement of calculation variables and data and its size is determined by the number

6、of slaves. For 254 oscillators, 32Kbytes of RAM are sufficient. The CPU SCI communication port is used to link the IS1 board to the serial bus. The SCI port is linked to the serial bus through two drivers (74HC541. The exchange of data between the PC and the IS1 is done through two latches, one that

7、 receives an 8-bit word from the PC which is then read by ISI, and the other for the other direction of data transfer. A hardware interrupt request is placed every time data is placed in a latch. The request is deactivated when the latch is read and the latch is then ready for receiving the next byt

8、e of data. The Intelligent Analog Multiplexer Board The IAM board (Fig. 4 enables the link between oscillators' signal outputs and the frequency counter input. Since it is located inside the temperature chamber, it should have a wide operating temperature range. The main part of the IAM board is

9、 the same microprocessor used in pCTCXOs. It communicates with the PC through its SCI port in the same way that the pCTCXOs do. After being addressed (its address is 00, it receives data containing the address of the oscillator whose output should be connected to the frequency counter. The data is c

10、onverted into an address code that is sent to the analog multiplexer through the microprocessor's PORT B. The output of the analog multiplexer is linked directly to the frequency counter input. The size of the analog multiplexer depends on the number of oscillators to be calibrated simultaneousl

11、y, which in turn depends on the capacity of the temperature chamber. For larger capacity chambers, an analog multiplexer tree would be used. The ACL Software The ACL software is divided into four parts: 1 PC software, 2 IS1 software, 3 IAM software, and 4 pCTCXO's calibration mode software. The

12、pCTCXO's calibration mode software was already described in Section 11. A short description of the other three parts follows. PC Software PC software controls the operation of the temperature chamber and frequency counter, and it supervises the calibration procedure and the operation of the syst

13、em as a whole. The program starts by reading the input parameters for the calibration process (temperature range, nominal frequency, frequency stability, etc. from a text configuration file. It then initializes and checks the measuring instruments, oscillators, resources and the IS1 board and downlo

14、ads the calibration mode software to the oscillators through the IS1 board. Then the calibration process begins as described earlier. The operation of the temperature chamber and the frequency counter is controlled by the PC software, but the calibration itself is partially controlled by the IS1 sof

15、tware. Authorized licensed use limited to: Institute of Science & Technology of China. Downloaded on March 20,2010 at 22:03:39 EDT from IEEE Xplore. Restrictions apply. HABIC et ai.:DESIGN OF MICROCONTROLLERTEMPERATURE COMPENSATED CRYSTAL OSCILLATOR AND AUTOMATIC COMPENSATION LINE 515 When all o

16、scillators are calibrated at all temperatures, the autonomous mode software for each oscillator is sent to the IS1 board, followed by the command for programming of the pCTCXO's EEPROM's one at a time. The program ends by reinitializing of all instruments and writing an output text file cont

17、aining all relevant information about the calibration process for future reference, statistics, and checking. Aflf PPml 05 04 03 02 01 0 ISI Software The IS1 software consists of seven routines, each initiated by a corresponding command received from the PC. The first one is for sending IS1 status t

18、o the PC. The second and third routines are for receiving from the PC the autonomous mode software (together with the corresponding look-up table formed during the calibration process and calibration mode software, respectively. The fourth routine is for downloading the calibration mode software to

19、all oscillators. The fifth routine is for checking the operation of the serial bus and oscillators. The sixth and longest routine (ISICAL is for calibration of the oscillators. Its operation is interactive with the PC software. ISICAL starts with sending the command to the IAM telling it which oscil

20、lator's output to connect to the frequency counter. Then the PC is informed that it can start with the frequency measurement and it sends the frequency value to the IS1 board. ISICAL then calculates the needed voltage value to pull the frequency back to the nominal value and sends it to the osci

21、llator under calibration. The process is repeated until the target frequency is achieved. The corresponding temperaturevoltage pair is saved in the IS1 RAM and the calibration of the next oscillator begins. The routine ends when all oscillators are at their nominal frequencies. The last routine is f

22、or downloading the autonomous mode software to the oscillators. The downloading process is done for each oscillator separately, since the look-up tables differ from oscillator to oscillator. -0 1 -0 2 -0 3 -0 4 -0 5 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Temperature "C Fig. 5. Frequen

23、cy to temperature characterlstlc of compensated pCTCXOs. -3 ' I m ' I 1 1 -4 -5' 4 ' I A ' ' 1 ' I -50-40 -30 -20-10 0 10 20 30 40 50 60 70 80 90 ' ' - T e m E t u r e "C Attempt1 Aacmpt2 Attempt3 A m p 1 4 A m p i s A m p 6 Attcmpt7 Aarmpt8 Fig. 6. Convergen

24、ce of the frequency offset during calibration. curves with a maximum frequency deviation A f / f = f 2 5 ppm and a maximum slope ( A f / f / A T = 1.8 ppm/OC. The entire pCTCX0 is encapsulated in a standard 36 mm x 27 mm x 19 mm size case. The crystal units used in our test oscillators were high qua

25、lity crystal units, with compound unwanted frequencytemperature curve deviations (hysteresis, activity dips, etc. below 0.1 ppm. If lower quality crystal units are used or a higher stability oscillator is required, a higher order A/D IAM Software converter would be used. There was no need to leave r

26、oom At the start of the IAM main program the initialization of for the errors due to the trimming of oscillators to nominal all resources and variables is done. The program then waits frequency, since the oscillators are sealed before the comfor an interrupt request that is automatically activated e

27、ach pensation process, thus the trimming is not necessary at the time a character is received through the serial bus. If the time of production. Obviously, the trimming effect due to character is an address and it is equal to $00 (IAM address, trimming necessary to correct frequency drift due to agi

28、ng will the appropriate variable is set. If the character is data, and degrade the stability of oscillators as in all other compensation the IAM was already addressed, the character is transferred methods. If this degradation of frequency stability can not be to PORT B, thus selecting the applicable

29、 osci11ator's output. tolerated, correction of the frequency drift due to aging can be The variables are then reset and the next interrupt request is done by recalibration instead of by trimming capacitor. Frequency excursions of one of the sample pCTCXOs monitored. during calibration is present

30、ed in Fig. 6. The number of attempts to obtain nominal frequency at a selected constant IV. EXPERIMENTAL RESULTS temperature depends on the closeness of the varactor voltage A frequency stability better then f0.5 ppm in the range of starting value and its final value. The diagram also illustrates op

31、erating temperatures from -40°C to f85"C was obtained the convergence of the shortened successive approximation with a 9-bit A/D converter and 10-bit pulse-width D/A con- algorithm. The ACL system calibration time for three pCTCXO deverter (Fig. 5. The 25 point look-up table was obtained f

32、or AT-cut crystals with uncompensated frequency to temperature vices is shown in Fig. 7. The dark rectangles represent the time Authorized licensed use limited to: Institute of Science & Technology of China. Downloaded on March 20,2010 at 22:03:39 EDT from IEEE Xplore. Restrictions apply. 516 IE

33、EE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 42, NO. 4, JULY 1995 Time min REFERENCES 11 M. E. Frerking, "Method of temperature compensation," in Proc. 36th 30 Temperature "C _wy=m,um* -"m I _*- i l 7 Fig. 7. The ACL algorithm's time consumption

34、. interval needed for temperature stabilization of the temperature chamber and oscillators. The white rectangles designate time consumed by the ACL software during execution of the shortened successive approximation algorithm. The gray rectangles represent the time spent for settling after change of

35、 varactor voltage. The main problem in the design of a ACL system is to find an efficient calibration algorithm to save adjustment time. The phase noise of the pCTCXO output signal is high (-60 dB/Hz, f > 100 Hz due to low rejection of harmonics in the PWM output voltage used for D/A conversion.

36、This shortcoming may be avoided by using a classical resistive network D/A converter if the oscillator is used in applications requiring low phase noise. Annual Freq. Cont. Symp., 1982, pp. 564-570. 2 V. Candelier, G . Caret, and A. Debaisieux, "Low profile high stability digital TCXO; ultra lo

37、w power consumption TCXO," in Proc. 43rd Annual Freq. Cont. Symp., 1989, pp. 51-53. 3 R. Rubach, "Dual mode digitally temperature compensated crystal oscillator," in Proc. 36th Annual Freq. Cont. Symp., 1982, pp. 571-575. 4 E. K. Miguel, "A temperature compensated SC cut quartz c

38、rystal oscillator," in Proc. 36th Annual Freq. Cont. Symp., 1982, pp. 576-585. 5 T. Uno and Y. Shimoda, "A new digital TCXO circuit using a capacitorswitch array," in Proc. 37th Annual Freq. Cont. Symp., 1983, pp. 434-441. 6 2. AleksiC, D. VasiljeviC, A. PavasoviC, "Digital tempe

39、rature compensation of crystal oscillators using temperature switches," in Proc. 40th Annual Freq. Cont. Symp., 1986, pp. 340-343. 7 T. Miyayama, Y. Ikeda and S. Okano, "A new digitally temperature compensated crystal oscillator for a mobile telephone system," in Proc. 42nd Annual Fre

40、q. Cont. Symp., 1988, pp. 327-333. 8 A. Benjaminson and S. C. Stallings, "A microcomputer-compensated crystal oscillator using a dual mode resonator," in Proc. 43rd Annual Freq. Cont. Symp., 1989, pp. 2G26. 9 R. L. Filler, J. A. Messina, and V. J. Rosati, "Frequency-temperature and ag

41、ing performance of microcomputer-compensated crystal oscillators," in Proc. 43rd Annual Freq. Cont. Symp., 1989, pp. 27-33. IO M. Bloch, M. Meirs, J. Ho, J. R. Vig, and S. Schodowski, "Low power timekeeping," in Proc. 43rdAnnual Freq. Cont. Symp., 1989, pp. 34-36. 111 M. E. Frerking,

42、Crystal Oscillator Design and Temperature Compensation. New York: Van Nostrand Reinhold, 1978. Dejan Habif received the B.E. and M.E. degrees in electncal engineering from the University of Belgrade, Belgrade, Yugoslavia in 1989 and 1993, respectively. His research interests are in the area of indus

43、trial electronics. V. CONCLUSIONS This paper describes a new concept in the design of a temperature compensation network in microcontroller compensated crystal oscillators (pCTCX0. Oscillators are designed in such a way as to make compensation procedure as simple as possible. A new concept of a prod

44、uction line for automatic oscillator calibration is also described. The oscillators under calibration form an integral part of the ACL, and they perform a part of the compensation procedure. The pCTCXO compensation circuit is built using a general purpose low cost microcontroller. It is a small, int

45、elligent unit able to communicate with the outside world. The proposed concept provides fully automated, unsupervised temperature compensation of sealed crystal oscillators without component selection in a single temperature run. Many oscillators may be calibrated simultaneously in production and later, during use. Both digital compensation approaches are supported: dual mode MCXO and classical, temperature dependent voltage generation for VCO input control. Efficient shortened successive approximation algorithm provides fast and reliable convergence. Upgrading of a standard