Programmable frequency synthesizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Application of microcircuits

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Readers are offered a description of a frequency synthesizer up to 950 MHz, which can be used as fixed or swept frequency generators in measuring technology, as well as in receiving and receiving-transmitting equipment. The use of specialized microcircuits greatly simplifies the manufacture of the device and makes it easier to work with it.

The frequency synthesizer is built on the basis of two specialized microcircuits - the KR1830BE751 controller and a single-chip frequency synthesizer.

KF1015PL2. The device, together with a voltage controlled generator (VCO), can be used as:

• frequency generator in the range of 50...950 MHz;
• swept frequency generator;
• generator in radio receiving and receiving-transmitting devices.

The programmable controller allows you to:

• direct dialing of the frequency 50...950 MHz and its indication with the formation of a code on the synthesizer;
• frequency grid step selection -100 Hz... 1 MHz;
• selection of the division factor of the reference oscillator of the KF1015PL2 microcircuit 10, 20, 40, 100, 200, 400, 800, 1000;
• intermediate frequency (IF) set higher or lower relative to the indicated frequency and multiple of the frequency grid - 100 Hz ... 900 MHz;
• a set of transmitter frequency detuning above or below the reception frequency in multiples of the frequency grid - 100 Hz ... 900 MHz;
• selection of initial and final frequencies for frequency scanning mode - 50...950 MHz;
• selection of the initial and final "lines" of memory for the scanning mode using the built-in frequency memory - 0...9 (0...99 with external memory).

Memory capacity of frequency values ​​(number of "lines" in memory) - 10 (with external memory - 100).

The time for generating a new frequency code is 28 ms.

With a stabilized supply voltage of 5 V, the device consumes a current of 12 mA, with external memory - 14 mA. In standby mode (micro consumption mode), the current consumption is reduced to 15 μA.

The device consists of a synthesizer controller, a keyboard, an indication unit, a frequency synthesizer, and a voltage regulator of the power supply.

The purpose of the pins of the KR1830BE751 chip is given in Table. one.

The electrical circuit for switching on the controller is shown in fig. 1. Its main purpose is to generate a code for a frequency synthesizer chip.

Fig.1 (click to enlarge)

The output of the code to the synthesizer is carried out each time after changing the following parameters:

• current frequency;
• grid step (Grid); - division ratio of the reference divider (CD);
• intermediate frequency (IF);
• frequency detuning (Funset).

For the case of using extended memory, the output РЗ.3 of the DD1 chip (polled by the controller once when the power is turned on for the first time) is connected to a common wire and contains an additional register DD2 and a memory chip DD3. Without external memory, the controller can memorize 10 numerical frequency settings (10 "lines"). In this case, microchips

DD2, DD3 are excluded, and the output RZ.3 DD1 must be disconnected from the common bus. The register is powered and the memory chip is selected only for the time of accessing the external memory (according to a signal from the P2.3 output of the controller).

To control the controller, a keyboard is used, the keys of which are assigned according to Table. 2.

Fig.2 (click to enlarge)

The electrical circuit of the keyboard is shown in fig. 2, and the diagram of its operation is shown in Fig. 3a. Time of protection against a bounce of contacts - 3 ms. The DD1 chip is used to input information from several nodes of the synthesizer: from the power source - about the transition to the micro-consumption mode; from a frequency synthesizer microcircuit - about switching to a new frequency with a guaranteed installation of the old frequency; from the receiver noise suppressor - about a temporary stop of scanning for 5 s. All active levels are low. The duration of the "micro-consumption" signal pulse must be at least 50 ms.

Ris.3

Visualization of the state of the controller is carried out using a liquid crystal indicator (LCI), which has eight familiarity and two special characters, for example, "E" and "M".

The display panel contains:

• frequency indicator (six familiarity) - to display various information;
• memory "line" number indicator (two familiarity) - to visualize the number of the working "line" of memory;
• "direction" indicator (sign "-")
• to visualize the scanning direction, the sign of the intermediate frequency and the sign of the transmitter detuning;
• "error" indicator ("E" sign) - to visualize an error when calculating the frequency synthesizer code;
• indicator "block detuning" (sign "M") - to visualize the inclusion or deactivation of detuning.

The electrical circuit of the indicator on the ILC is shown in fig. 4, and the diagram of indicator control signals - in fig. 3b.

Fig.4 (click to enlarge)

The operation of the indicator is controlled by the phase method with the formation of a voltage value equal to half the supply voltage for common electrodes: A, F, -, M; E, G, B; C, D, H. Any segment is activated when the common electrode and the electrode of the corresponding digit are switched inversely switching voltage levels and is not activated when acting in phase. In the time intervals T1, T2, T3, voltage is applied to the segments of one polarity, and in the intervals T4, T5, T6 - the other. During the T7 interval, all electrodes are at a low level and the indication is turned off. The segments of all eight digits are controlled in parallel. Registers DD1 - DD4 convert the controller's serial signal code into a three-level one. The operating frequency of the indicator switching is 50 Hz, the duty cycle is 3. The use of precise resistors (with a tolerance of ±1%) practically eliminates the flow of the direct current component from the unbalance of the control voltage.

Current consumption - 60 uA.

Authors: V. Semenov, V. Shlektarev, Pushchino, Moscow Region; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Application of microcircuits.

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