Sinusoidal generator on a digital microcircuit. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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In amateur radio practice, no, no, and you will need a simple generator of sinusoidal oscillations. It's good if "something" industrial is at hand, otherwise a long and tedious study of literature begins. Often, after the necessary scheme is found and assembled, there is no strength or desire left to deal with tags, for which all this was started.
In 9 cases out of 10, nothing "advanced" is required from a sinusoidal generator. For example, to check the input driver of the frequency meter, and in many other cases, you should use the proposed scheme. Its undoubted advantage is simplicity. Despite its unusual appearance, the scheme is quite reliable, the author has been using it for about 2 years.
The main element of the generator is the K155LAZ chip. The ring connection of three inverters DD1.1...DD1.3 is an unstable structure, prone to excitation at the maximum operating frequency. Resistor R1 sets the operating point of the microcircuit near the switching threshold. Due to the presence of a "dead zone" in TTL circuits (voltage range between the thresholds of logical "0" and logical "1"), the IC goes into active mode. The L1-C1 circuit creates the conditions for excitation at its own resonant frequency. The quality factor of the circuit does not matter much, the circuit starts up confidently with low-quality circuits.
The frequency stability depends solely on the stability of the circuit and is quite high. The amplitude of the output voltage depends on the quality factor of the circuit and can reach 2,5 V. At the maximum frequency (about 10 ... 15 MHz), the amplitude of the pulses is 2 times less, and the microcircuit starts to heat up.
The output signal can be taken both from the coil L1 and from the capacitor C1. However, it is better to remove it from the coil, in which case the load capacitance (even a very significant one) has a minimal effect on the operating frequency. Despite this, it is better to connect the load through a buffer. It can be an emitter or source follower, an op-amp buffer or a coupling coil - it all depends on the output frequency. Obviously, at a frequency of 1 kHz, the op-amp should be preferred, and at 5 MHz, the coupling coil.
Establishing the circuit is reduced to the selection of the operating point of the IC using the resistor R1. To do this, an oscilloscope is connected to the generator output and, by rotating R1, a stable generation with maximum amplitude is achieved. R1 is better to take a multi-turn, such as SPZ-39.
The device is operable with any TTL- and TTLSH-series inverters. It is better to refuse the use of CMOS microcircuits, because. it is almost impossible to achieve stable generation on them.
Author: A.Uvarov, Belgorod
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