Digital frequency multiplier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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Digital division of a stable signal frequency, for example, using counters or flip-flops, is widely used in amateur radio practice. This technique is used when the frequency of the master oscillator, stabilized by a quartz resonator, must be reduced by an integer number of times. Much less often, digital multiplication of the signal frequency is used, which in some cases turns out to be useful. For example, if you cannot find a suitable resonator, it is better to first increase the frequency using a multiplier, and then divide it to the required value. Such a device is described

Readers are offered a variant of a digital frequency converter. Let's consider the principle of signal formation on the example of synthesizing the frequency 523,3 Hz of a "singing" tuning fork. It is described in the article "Tuning fork of a musician and singer" ("Radio", 1998, No. 10, pp. 62, 63). The author calculated: if the frequency of the widespread "clock" resonator 32 Hz is first multiplied by 768, and then divided by 10, we get a frequency of 626 Hz, which is equal to the frequency of the note "to" the 523,5nd octave with an error of 2%. A diagram of a different part of such a device from the basic version (see the article mentioned above) is shown in fig. 0,04.

(click to enlarge)

Of greatest interest is the frequency multiplier on the elements of the DD5 microcircuit, to the input of which, through the C5R5 differentiating circuit, a rectangular signal with a frequency of 32 Hz comes from the output of the DD768 microcircuit. The shaper, assembled on capacitor C1, resistor R5 and element DD5, for each positive drop at the input, generates a low-level pulse with a duration of about 5.1 μs. It acts on the lower (according to the circuit) input of the DD1,5 element, which, together with the elements DD5.2, DD5.3, capacitor C5.4 and resistor R6, forms a conventional rectangular pulse generator. The generator is tuned to a frequency of approximately 6 Hz, which corresponds to a pulse repetition period of about 27 microseconds. However, due to the shaper, this not entirely accurate frequency turns on average into a stable one, since with every tenth pulse the phase of the generator oscillations is adjusted.

Let us assume that the repetition period of the generator pulses is slightly more than 3,05 μs. Then, due to the shaper, every tenth low-level pulse will be shorter than the others (Fig. 2, a). If the period is slightly less than 3,05 μs, every tenth high-level pulse will become longer than the neighboring ones (Fig. 2, b). As a result, for each input synchronization pulse with a period of about 30,5 μs, ten output pulses will be generated, and their repetition period will, on average, be equal to the required one.

Chips DD2, DD3, trigger DD4.1, resistor R3 and diodes VD1-VD4 form a frequency divider of 327 680 Hz by 313, and trigger DD4.2 - by 2. From the direct and inverse outputs of the latter, a rectangular signal is fed to the base of transistors VT1- VT4 push-pull bridge amplifier AF, the load of which is a variable resistor R4 - volume control - and a piezoelectric emitter HA1.

Setting up the frequency converter is easy. First, the resistance (smaller) of the resistor R6 is selected, in which the multiplier operates in the frequency multiplication mode by 11, which corresponds to the extraction of the "intermediate" tone by the tuning fork, which is closer to the note "re" than the "c sharp" of the 2nd octave. Then, a resistance (greater) of the same resistor is selected, in which the multiplier operates in the frequency multiplication mode by 9, and the tuning fork plays a note just above the "b flat" of the 1st octave. Suppose that in the first case the resistance is 68 kOhm, and in the second - 82 kOhm. Therefore, the average resistance of the resistor R6 is 75 kOhm - it is installed in the device. Now the multiplication factor, no doubt, will be 10, and the tuning fork will emit a note "to" the 2nd octave.

Author: V.Bannikov, Moscow

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