Synchronous detector with voltage doubling. Scheme, description

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Synchronous detector with voltage doubling. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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A scheme of a full-wave synchronous detector with voltage doubling is presented, which makes it possible to detect both orthogonal components of a harmonic signal using a single microcircuit.

A synchronous detector makes it possible to obtain information about the amplitude and phase of the received signal, as well as to suppress accompanying noise [1]. For this reason, various types of synchronous detectors are widely used in modern technology. However, the use of an unsuccessful version of the synchronous detector may prevent the expected results from being obtained.

First of all, one should warn against the use of a half-wave synchronous detector [2]. Figure 1 shows its diagram.

Fig. 1

It consists of an electronic (or mechanical) key Kl and a simple low-pass filter RC, and the role of resistor R is most often performed by the internal resistance of the input signal source and the public key.

Rice. 2 illustrates its operation and is self-explanatory. The disadvantage of such a detector is manifested in the presence in the input voltage Eux, along with the useful signal, of an alternating voltage with a frequency much lower than the frequency of the useful signal (for example, infra-low-frequency noise of the input stage).

Fig. 2

On fig. 3 shows a positive half-wave of such a voltage.

Fig. 3

As can be seen from the figure, the interference voltage passes almost unhindered through the half-wave synchronous detector, depriving it of frequency selectivity.

A full-wave synchronous detector inverts even or odd half-cycles of the input signal [3] with their subsequent summation. This not only increases the useful signal conversion factor (Fig. 4), but also eliminates interference from low-frequency (relative to the signal) voltages, as shown in Fig. 5. XNUMX.

Fig. 4

Fig. 5

There are many varieties of published schemes of full-wave synchronous detectors [3-5]. As a rule, this is a differential operational amplifier with alternating supply of half-periods of the detected signal to the inverting and non-inverting inputs, carried out by electronic keys. Thus, to detect one component of the useful signal, an operational amplifier chip and an analog key chip (or discrete field-effect transistors) are required, not counting numerous resistors and capacitors ("strapping").

The author proposes for use a simpler and more efficient scheme of a full-wave synchronous detector with voltage doubling. It is based on the well-known full-wave diode rectifier with voltage doubling [6], in which the rectifier diodes are replaced by electronic switches. Despite the triviality of such a circuit solution (Fig. 6), it has not been found in the literature known to the author.

Fig. 6

Here, in the odd half-cycles of the useful signal, the capacitor Cfl is charged to its amplitude value, and in the even-numbered half-cycles, the useful signal, in total with the received charge, is fed to the output of the device. On fig. Figure 7 shows an example of the implementation of a full-wave synchronous detector with voltage doubling, which detects the in-phase and quadrature components of a useful signal on a single microcircuit of the K561KP1 analog switch (foreign analogue is the CD4052BC microcircuit).

Fig. 7

Switching voltages with useful signal frequency f and twice the frequency 2f are usually easy to obtain using a frequency synthesizer or microcontroller.

The proposed detector has been used in dozens of magnetometers and metal detectors at frequencies from tens of hertz to tens of kilohertz and has proven itself well.

Literature

J. Max. Methods and techniques of signal processing in physical measurements, vol. 2. - M.: Mir, 1983.
V. A. Bogdenko. Ferroprobe magnetometer with a miniature sensor. Instruments and Experimental Technique, 1993, No. 3, pp. 157-160.
G. Petin. Key synchronous detector. Circuitry, No. 3,2003, 14, p. 15-XNUMX.
V. S. Gutnikov. Integrated electronics in measuring devices. - L .: Energoatomizdat, 1988.
A. I. Shchedrin. New metal detectors for searching for treasures and relics. - M.: Hotline-Telecom, 2003.
A. A. Kulikovsky (ed.). Handbook of the radio amateur. - M.: GEI, 1961.

Author: Yu.Reutov, Ekaterinburg

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Comments on the article:

Erg
The pictures do not match the article.

Diagram
2Erg Thanks, fixed.

Onetech
It's really awesome. It's strange why it doesn't apply. But still, I would turn on the capacitor differently. It is better to put a small-capacity capacitor (conditionally pumping) with one output on the ground, with the second output on the switching "contact" of the mux. In this case, one of the "contactors" of the mux must be connected to the URF (input) and the second to the filtering (output, relatively large capacity) capacitor.

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