Additive Triangle Signal Conditioner

Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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The possibility of synthesizing a triangular-shaped signal by adding two sinusoidal signals of different polarity rectified by bridge circuits, one of which is shifted in phase relative to the other by 90°, is shown; formulas are given that describe the dynamics of signal addition processes; on the basis of theoretical calculations, a circuit of a device synthesizing a triangular signal was created.

Triangular-shaped signals are usually obtained in generators using time-charging RC circuits, digital-to-analog converters, or synthetically by hardware and software. In this case, as a rule, it is difficult to achieve high linearity and symmetry of the generated signal; it is possible to solve the problem due to a noticeable increase in the intellectual and resource intensity of the device [1–4].

It turned out to be quite simple to obtain a signal of an almost ideal triangular shape when using a frequency doubler, the scheme of which was proposed in the early 70s of the XX century (private communication, frequency doubler by S.I. Semenov). The principle of operation of this doubler is based on the antiphase addition of two sinusoidal signals rectified by bridge circuits, one of which is shifted in phase relative to the other by 90 °. Despite the simplicity of such a frequency doubler, until recently, its practical implementation and, moreover, analytical studies have not been performed.

Computer modeling of the shape of signals taken from the output of such a device showed that at the output of the shaper, when a phase shift of 90° is provided, a triangular signal is obtained. The block diagram of the triangular-shaped additive signal generator is shown in fig. 1. The dynamics of electrical processes observed at various control points of the device can be described by the following expressions:

U1(t) = U0 sin(wt), U2(t) = U0 sin(wt + 90), U3(t) = U0 abs[sin(wt + 90)], U4(t) = -U0 abs(sin wt), U5(t) = U0 {abs[sin(wt + 90)] - abs(sin wt)}. In general, Uout(t) = U0 {abs[sin(wt + n90)] - abs(sin wt)}, n=1,3,5...

(1) (2) (3) (4) (5)

Fig.1. Structural diagram of the shaper

A sinusoidal signal (1), taken from the output of generator 1 (Fig. 1), is fed to phase shifter 2 and resistive voltage compensator 4. A sinusoidal signal (90) shifted in phase by an angle of 2 ° is fed to diode-bridge circuit 3. The signal from voltage compensator 4 is fed to the second back-connected diode-bridge circuit 5. Thus, rectified bipolar signals (3) and (5) are formed at the outputs of diode-bridge circuits 3 and 4. These signals are summed up in the adder 6, thus forming a triangular-shaped output signal (5) at the load resistance Rload - Diagrams of the output signals with varying phase shifts are shown in Fig.2.

Fig.2. Output diagrams

A practical circuit of a frequency doubler - a triangular shaper is shown in Fig. 3. The input signal of a sinusoidal form through the phase-shifting chain R1C1 is fed to the first rectifier bridge (diodes VD1-VD4). The same signal through the potentiometer R2 ("Compensation") is fed to the second rectifier bridge (diodes VD5-VD8).

Fig.3. Schematic diagram of the triangular waveform generator

At the outputs of the bridges relative to the common bus, rectified signals of the double frequency of the bipolar voltage are formed. The outputs of the bridges are connected through the potentiometer R3 ("Balance"), between the engine of which and the common bus the load resistance is connected.

A sinusoidal signal with a frequency of 3 kHz and a voltage of 5 V is fed to the input of the shaper (Fig. 2). The device is tuned by sequentially adjusting the tuning elements (resistors R1-R3). Potentiometer R1 adjust the phase shift; R2 - compensate for the loss (attenuation) of the signal when the signal passes through the phase-shifting chain; R3 - balance the amplitude of the mixed signals. As a result, a triangular-shaped signal of doubled frequency (10 kHz) is formed at the output.

The operation of the device was tested using the Electronics Workbench 5.12 circuit simulation program.

The advantages of the described scheme for obtaining triangular signals include its simplicity and high linearity of the output signal. At the same time, a triangular-shaped output signal close to ideal is provided in a narrow frequency band, which is due to the use of phase-shifting chains of the simplest type, intended only to demonstrate the principle of operation of the device. The range of operating frequencies at which the shaper is capable of operating is also limited by the frequency properties of the rectifier diodes (the upper limit approximately corresponds to a value of 5 ... 10% of the limiting operating frequency of the diodes used).

Thus, to provide the required signal shape, the device elements must meet a certain set of requirements due to the presence of semiconductor non-linear elements:

- ideality of rectifiers (linearity and identity of their volt-ampere characteristics);
- minimum and equal capacitance of n-p transitions (identity of volt-capacitance characteristics).

These requirements are partly satisfied when using high-frequency germanium point diodes of the same production batch, selected according to the criterion of identical current-voltage and volt-capacitance characteristics, as well as when operating in the region of relatively low frequencies (up to units of kilohertz), using a high-amplitude sinusoidal signal (units. ..tens of volts) and work on a matched load.

It is possible to improve the shape of the output signal peaks (the area of ​​low voltages of rectified signals, where the nonlinear properties of semiconductor rectifiers are most clearly expressed) by shifting the operating points of the diodes to the linear section of the current-voltage characteristic by feeding with direct current.

Literature

1. Bondar V.A. Study of the linearization of the process of charging or discharging a capacitor in linearly varying voltage generators: Abstract of the thesis. diss. For the degree of Cand. tech. Sciences. - Tomsk: TPI, 1971.
2. Notkin L.R. Function generators and their application. - M.: Radio and communication, 1983.
3. Graf R., Shiite V. Encyclopedia of electronic circuits. T. 7.Ch. I.-M.: DMK, 2000.
4. Shustov M.A. Phase modulated triangular voltage generator. - Radio amateur, 1999, No. 5.

Author: M.A. Shustov; Publication: radioradar.net

See other articles Section Knots of amateur radio equipment. Generators, heterodynes.

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