- Detail

Design of low-frequency signal generator

Abstract: signal generators are widely used in electronic engineering, communication engineering, automatic control, telemetry control, measuring instruments, instruments, computers and other technical fields. A simple signal generator that can transform triangle wave, sine wave and square wave is designed by combining integrated operational amplifier with discrete components, using hysteresis comparator circuit to generate square wave signal, and making full use of differential circuit for circuit conversion. Through the circuit analysis, the parameters of components are determined, and the ideal output results of the circuit are simulated by Multisim software, which overcomes the technical problems existing in the design of low-frequency signal generator circuit, and makes the design of low-frequency signal generator simple in structure and convenient to realize. The design can produce waveform output below 10 Hz, and has been applied to experimental operation

key words: signal generator; Square wave signal; Circuit simulation; Hysteresis comparator

o introduction

signal generator generally refers to a circuit or instrument that can automatically generate sine wave, square wave and triangular wave voltage waveforms. The circuit form can be composed of operational amplifier and separation elements; Monolithic integrated function generator can also be used. Here, a signal generator that can generate three common experimental waveforms is designed by using discrete components, and the parameters of each component are determined. Through adjustment and analog output, the circuit can generate three signal outputs with a frequency lower than 10 Hz, which has the advantages of simple principle, clear structure and low cost. The circuit has been used in the experimental operation of the actual circuit

1 waveform conversion principle

1.1 generation of square wave and triangular wave

square wave triangular wave sine wave signal generator circuit is composed of operational amplifier circuit and discrete components, and its structure is shown in Figure 1. It uses comparator to produce square wave output; Square wave generates triangular wave output through integration

1.2 use the differential amplifier circuit to realize the transformation of triangular wave to sine wave

the principle of waveform transformation is to use the nonlinearity of the transmission characteristic curve of the differential amplifier, and the waveform transformation process is shown in Figure 2. It can be seen from Figure 2 that the more symmetrical the transmission characteristic curve is, the linear region is 2 Weight of auxiliary impact hammer: 40kg. The narrower the range, the better; The amplitude UIM of the triangular wave should just make the crystal close to the saturation region or the cutoff region

2 circuit design and parameter adjustment

according to the design function, The design process of the circuit is divided into low-speed pin plate (it has three parts: sine wave, square wave and triangle wave of large and small stocks.

2.1 generation and conversion circuit of square wave and triangle wave

in Figure 3, U1 forms an in-phase input hysteresis comparator circuit for generating output square wave. Operational amplifier U2 forms an integral circuit with resistance RP2 and capacitance, which is used to take the square wave output by U1 circuit as input to generate output triangle wave.

the parameters of square wave part and triangle wave part are determined as follows :

according to the performance index, it can be seen that f is proportional to C. to obtain l~10 Hz output, c=10 f; To get 10 ~ 100 Hz output, c=1 F. At this time, r4+rp2=7.5 ~ 75 K. if r4=5.1 K is taken, the pressure range of R belongs to the safe range p2=2.4 K or rp2=69.9 K, because when rp2=100 K,

according to the output triangle amplitude of 5 V and the output square wave amplitude of 14 V, if there is: R2/(r3+rp1) 14=5 R2/(r3+rp1) = 5/14, r2=10 K, then there is rp1xxxxxx △ 47 K, r3=20 K. According to the rise time of the square wave is 2 ms, you can choose the 74141 model op amp. Thus, the adjustment resistance is:

2.2 sine wave generation circuit

sine wave generation circuit is shown in Figure 4. Since the differential amplification circuit is selected to transform triangle wave to sine wave, ksp2222a tube is selected, and its static curve image is shown in Figure 5

according to the static characteristic curve of ksp2222a, the center static current and voltage of the static working area are selected as:

because the static working point has been determined, the static current becomes known. According to KVL equation, we can calculate the size of each resistance value in the mirror current source:

2.3 system integration

centralize each sub circuit on a circuit board. After sharing the power supply and grounding terminal, the structure of the whole signal generator becomes compact and beautiful. The integrated electricity can be processed by traditional thermoplastic molding methods such as injection, extrusion and molding. The circuit diagram is shown in Figure 6

3 simulation experiment results and analysis

3.1 simulation results

draw the circuit diagram with Multisim software, connect the oscilloscope at the corresponding point, and simulate the circuit results

the output results of changing the value of RP2 from 2.4 K to 5.6 K are compared as follows

3.2 result analysis

(1) frequency range

to facilitate measurement, connect the square wave signal on the circuit diagram to the oscilloscope, close the switch c1=10 F, disconnect the switch c2=1 F, and then adjust RP2 and measure the variation range of the square wave signal frequency at this time; Disconnect the switch of C1, close the switch of C2, adjust RP2 in the same way, and record the variation range of square wave signal frequency. The results are shown in Table 1. The comparison of the three output waveforms of the circuit is shown in Figure 7

(2) the output voltage

square wave signal is connected to the oscilloscope, and the RPL is adjusted to obtain the square wave peak vpp=14 V; Remove the square wave signal and connect the triangular wave signal, adjust RP1, and measure the peak value of triangular wave upp=5 V; Connect the sine wave signal to the oscilloscope, adjust RP3 and RP4, and measure the sine wave peak value upp=2.8 v

4 conclusion

the performance index of function signal generator mainly depends on the selection of components and parameters of circuit components. Connecting an oscilloscope in the circuit will have a certain impact on the load matching of the circuit, and then affect the waveform output. In this design, Muitisim software is used to simulate the designed circuit, and the results are simulated. The circuit can produce three signal waveforms lower than 10 Hz, and the output voltage can reach a reasonable range. This circuit has been applied to experimental operation

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