Design and implementation of function generator based on 5G8038

The function generator is a basic waveform generator often used in scientific research and production. With the rapid development of large-scale integrated circuits, multi-functional signal generators have been made into application-specific integrated circuits, such as the domestically produced 5G8038 monolithic Function waveform generator can generate high-precision sine waves, square waves, rectangular waves, sawtooth waves and other signals. This product has the same function as the foreign ICL8038. The various signal frequencies of the product can be adjusted by adjusting the parameter values ​​of external resistors and capacitors, which provides great convenience for quickly and accurately realizing the function signal generator.

This article mainly introduces a multifunctional function signal generator composed of operational amplifiers LM318 and 5G8038, potentiometers, etc. This circuit can generate sine wave signals, triangle wave signals, and rectangular wave signals with adjustable frequency and duty cycle. Its output frequency can Continuously adjust within the range of 20Hz-5kHz to achieve the advantages of simple debugging, stable performance, and ease of use.

1 Characteristics of 5G8038 [1]

The performance characteristics of 5G8038 are as follows:

(1) The frequency drift of various output waveforms is less than 50×10-6Hz/℃;

(2) By adjusting the value of external resistor-capacitor components, it is easy to change the oscillation frequency to make the work The frequency is adjustable within the range of 0.001Hz-300kHz.

(3) The output waveform distortion is small;

(4) The linearity of the triangular wave output can be better than 0.1%.

(5) The rectangular pulse output duty cycle adjustment range can reach 1-99%, and narrow pulse, square wave, and wide pulse output can be obtained;

(6) The output pulse (or square wave) level can be from 4.2-28V;

(7 ) The peripheral circuit is simple (fewer external components), the lead wire is more flexible and has strong applicability.

5G8038 is produced by Shanghai Component Factory No. 5, and the performance characteristics of the similar product ICL8038 produced abroad are better than those used interchangeably. The 5G8038 pin arrangement is shown in Figure 1.

Integrated circuit 5G8038 pin description:

1: Sine wave distortion adjustment terminal;

2: Sine wave output terminal;

3: Triangular wave/sawtooth wave output terminal;

4: Constant current source adjustment (pins 4 and 5 are connected to external resistors to adjust the duty cycle);

5: Constant current source adjustment (external resistor terminal);

6: Positive power supply;

7: Reference source output;

8: FM control input terminal;

9: Square wave/rectangular wave output terminal (open collector output);

10: External capacitor C;

11: Negative power supply or ground terminal;

12: Sine wave distortion adjustment;

13: Vacant end;

14: Vacant end.

2 Typical applications of 5G8038 - forming a multi-functional signal generator

(1) The internal structure [2] and working principle of the 5G8038 multi-functional function generator are shown in Figure 2.

It can be seen from the schematic block diagram of the function generator composed of 5G8038: It consists of a constant current charge and discharge oscillation circuit and a sine wave converter. The constant current charge and discharge oscillation circuit generates square waves and triangle waves, and the triangle wave outputs sine waves through the sine wave converter. Wave. In the figure, the two comparators C1 and C2 form a reference voltage with a relatively strong window set at 2/3Vcc and 1/3Vcc respectively. The outputs of the two comparators control the set end and reset end of the RS flip-flop respectively. The two constant current sources I1 and I2 are responsible for charging and discharging the timing capacitor C, and the conversion of charging and discharging is controlled by the output of the RS flip-flop through the on or off of the electronic switch S. When the electronic switch S is turned off, the circuit charges the external capacitor C. When the electronic switch S is turned on, the capacitor C discharges. Therefore, if the circuit parameters are properly designed, a good triangular wave can be generated on the capacitor C. After the buffer, the capacitor C is discharged. pin output. In order to convert a triangular wave to a sine wave in a relatively wide frequency range, a polygonal approximate conversion network composed of a resistor and a transistor can be used to convert the triangular wave into a sine wave, which is output from pin 2. The signal used to control switch S, that is, the output of the RS flip-flop, is a square wave, which is output from pin 9 through the buffer.

The multifunctional signal generator composed of 5G8038 is shown in Figure 3.

In order to improve the load capacity of the signal source, the triangle wave and sine wave signals can be amplified through the LM318 high-speed operational amplifier and then output.

By adjusting the position of the potentiometer Rp1, the output oscillation frequency of the function generator can be adjusted, and the duty cycle of the output rectangular pulse wave can also be adjusted.

Adjust the potentiometer Rp2 to adjust the distortion of the output sine wave signal.

Adjust Rp3 and Rp4 to adjust the signal output amplitude.

The three potentiometers Rp1, Rp2 and Rp3 in the picture are precision multi-turn potentiometers.

In order to obtain the best characteristics of the oscillation signal, the current flowing through pins 4 and 5 of the 5G8038 integrated circuit cannot be too large or too small. If the current is too large, the linearity of the triangular wave will deteriorate, resulting in an increase in the distortion of the sine wave; if the current is too small, the influence of the leakage current of the capacitor will become greater. The optimal current flowing through pins 4 and 5 of the 5G8038 integrated circuit is 1μA-1mA.

3 Conclusions

In the design of this article, the 5G8038 monolithic function waveform generator is used, which can generate high-precision sine waves, square waves, rectangular waves, triangle waves, sawtooth waves and other signals, and has high temperature stability and frequency stability. sex. It is especially suitable for industrial control and electronic laboratories. When the output buffer circuit is independently configured with multiple channels, it can output three signals in multiple channels at the same time, which is easier to meet actual needs.