Microwave laboratory synthesizer. Encyclopedia of radio electronics and electrical engineering

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The problem of frequency stability in transceivers has always existed. At relatively low frequencies (up to 100-150 MHz), it was solved using quartz resonators, at higher frequencies (400 MHz) - using surface-acoustic wave resonators (SAW resonators), while high-Q dielectric resonators are often used to stabilize ultrahigh frequencies. ceramics or other high-quality resonators [1].

The described methods of stabilization with the help of passive components have their advantages - simplicity and relatively low cost of implementation, but their main drawback is the impossibility of any significant frequency tuning without changing the frequency-setting element - the resonator. The impossibility of fast electronic tuning of the operating frequency while maintaining its stability sharply limits the use of radio devices, not allowing, for example, to implement multi-channel.

The integrated frequency synthesizers of various foreign companies, which are now widely used, make it possible to carry out fast electronic tuning of the working frequency, including ultrahigh frequency, while maintaining its high stability. Such frequency synthesizers are of direct and indirect types [2]. The advantages of direct synthesis include high speed with a small frequency grid step, but due to the need to filter a large number of spectral components caused by numerous nonlinear signal transformations, direct synthesis devices are rarely used in microwave circuits [3]. For the synthesis of microwave frequencies, synthesizers of an indirect type, or synthesizers with a phase locked loop (PLL), are usually used.

There are two main types of integrated PLL synthesizers - programmable, in which the frequency values ​​are set by an external microcontroller via a three-wire bus, and non-programmable, where the division coefficients of the internal frequency dividers are fixed, and the reference frequency is set by an external quartz resonator. In simple microwave circuits, non-programmable integrated synthesizers are usually used, for example, MC12179 from Motorola [4], the disadvantages of which include the need for an accurate choice of a quartz resonator, which is not always possible. Programmable frequency synthesizers, such as the UMA1020M from Philips, do not have this drawback, and since modern communication systems always have a control microcontroller, it is technically easy to program such a synthesizer. Self-oscillators of the microwave range are used in the form of functionally complete modules made using hybrid technology [5].

An example of the application of the described solutions is a simple laboratory microwave synthesizer, which allows generating and stabilizing the frequency in the range of 1900 - 2275 MHz with high accuracy, proposed in this article.

The block diagram of the designed synthesizer is shown in fig. 1., appearance - in Fig.2. As you can see from their diagrams, the synthesizer consists of a voltage controlled oscillator (VCO or VCO) JTOS-2200 from Mini-Circuits JTOS-2200, an integrated frequency synthesizer UMA-1020M and a Z86E0208PSC microcontroller from Zilog.

The microwave signal generated by the VCO is fed to the output of the laboratory synthesizer and to the input of the main programmable frequency divider included in the UMA-1020M circuit.

The reference signal generated by the JCO-8 crystal oscillator is fed to an auxiliary programmable frequency divider, which is also included in the UMA-1020M circuit. Structural diagram of UMA-1020M is shown in fig. 3, detailed technical documentation for the UMA-1020M can be found on the manufacturer's website philips.de/. The coefficients of both dividers - main and auxiliary - are set by the Z86E0208PSC microcontroller on a three-wire (DATA data, CLK clock and write enable / ENABLE) bus. The block diagram of the Z86E0208PSC microcontroller is shown in fig. 4. The internal ROM of the microcontroller is sufficient for programming seven different frequencies and one test mode. Specific frequency values ​​(or test mode) are set by jumpers on the printed circuit board of the laboratory synthesizer.

Before loading the next frequency value into the integrated synthesizer, the microcontroller polls the port connected to the jumpers and, in accordance with the received data, selects one or another firmware. The new frequency value is set automatically when the synthesizer board is powered on. The synthesizer programming algorithm for the Z86E0208PSC microcontroller is shown in fig. 5, the listing of the program is given at institute-rt.ru/common/statyi/zsynt/prog.html.

More details about programming microcontrollers from Zilog can be found in [6, 7], full technical documentation is available at zilog.com.

A feature of the used JTOS-2200 VCO is the tuning voltage range: from 0.5 to 5 Volts. That is, if the tuning voltage value is less than 0.5 Volts, the manufacturer does not guarantee stable oscillation generation. The conducted experiments have shown the veracity of this statement.

The principle of operation of the PLL, as well as the method for calculating the feedback filter (Loop filter), are quite widely and repeatedly considered in the technical literature [8], therefore, this article is not considered. There are several free programs available for calculating feedback filters, which can be found online at analog.com or national.com.

To control the correct operation of the synthesizer circuit, an LED is installed on the board, the glow of which indicates an error in frequency synthesis. When the synthesizer is working correctly, the LED should not light, but this function can be disabled by software.

The cost price of the assembled laboratory synthesizer does not exceed $30. There are two ways to reduce the cost of the proposed device: firstly, you can combine the quartz source of the reference oscillations of the synthesizer and the microcontroller, while remembering that the maximum clock frequency of the Z86E0208PSC is 8 MHz, while for the UMA-1020M it can be in within 5-40 MHz. Secondly, VCOs can be developed independently on transistors or amplifying integrated circuits using the technique given in [9, 10].

Literature

1. Dielectric resonators / M.E. Ilchenko, V.F. Vzyatyshev, L.G. Gassanov and others; Ed. M.E. Ilchenko. - M.: Radio and communication, 1989. - 328 p.: ill. - ISBN 5-256-00217-1.
2. Pestryakov A.V. Integrated circuits for frequency synthesis and stabilization devices// Chip News. - 1996. - No. 2.
3. Lobov V., Steshenko V., Shakhtarin B. Digital synthesizers of direct frequency synthesis// Chip News. - 1997. - No. 1.
4. Wireless Semiconductor Solutions. Motorola. Device Data - Vol.1. DL 110/D, Rev 9.
5. VCO Designer's Handbook 2001. VCO/HB-01. Mini Circuits.
6. Gladshtein M.A. Microcontrollers of the Z86 family from Zilog. Programmer's Guide. - M.: DODEKA, 1999, 96 p.
7. The Z8 Application Note Handbook. Zilog. DB97Z8X0101.
8. Starikov O. PLL method and principles of synthesizing high-frequency signals//Chip News. - 2001. - No. 6.
9. Microwave Oscillator Design. Application Note A008 // Hewlett-Packard Co. - publication number 5968-3628E (6/99)
10. Shveshkeyev P. A VCO Design for WLAN Applications in the 2.4 to 2.5 GHz ISM Band//Applied Microwave&Wireless. - 2000. - No. 6. - P.100-115.

Authors: N.A. Shturkin, I.V. Malygin; Publication: cxem.net

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