Brief introduction to the principle of function signal generator

The signals required by science and technology and industrial applications are becoming more and more precise, which has promoted the development and promotion of function signal generators, and has become an essential tool in the fields of industrial production, product development, scientific research, etc. As a precision test instrument, it has been widely used in the electronics industry. According to the analysis of the principle of function signal generator, we know that the most commonly used one is the sawtooth wave signal generator as the time base circuit.

For example, when we need to measure the accuracy/performance/frequency of a certain signal, we need to find a signal reference to observe the movement law of the detection signal, and then use some display instruments (such as oscilloscopes/digital display instruments, etc.) to use the fluorescent screen to display the measured image and the image of the function signal generator for comparison, simplifying the function generator measurement work. Below I summarize some basic knowledge about function signal generators, including the principle and performance analysis of function signal generators, so that everyone can understand this instrument more intuitively.

Function signal generator can be used to test or repair the frequency characteristics, gain, and passband of low-frequency amplifiers in various electronic instruments and equipment. It can also be used as an external modulation signal source for high-frequency signal generators. As the name suggests, it can definitely generate function signal sources, such as sine waves of a certain frequency, some of which can be voltage output and some can be power output. Let's use a simple example to illustrate the principle of function signal generator.

a) The signal generator system mainly consists of the following parts: master oscillator stage, master oscillator output adjustment potentiometer, voltage amplifier, output attenuator, power amplifier, impedance converter (output transformer) and indicating voltmeter.

b) Working mode: When a small signal sine wave is input at the input end, the signal is transmitted in two paths. One path is a loop to complete the rectification and voltage doubling function and provide working power; the other path is capacitive coupling and enters the input end of an inverter to complete the signal amplification function. The amplified signal is processed by the gate circuit of the subsequent stage, converted into a square wave and then output. The output end is an adjustable resistor.

c) Working process: First, the master oscillator generates a low-frequency sinusoidal oscillation signal, which needs to be amplified by a voltage amplifier. The amplification factor must meet the voltage output amplitude requirement. Finally, the output attenuator is used to directly output the voltage that the signal device can actually output. The output voltage can be adjusted using the master oscillator output adjustment potentiometer.

It is generally managed by a single-chip microcomputer, mainly to achieve the following functions:

a) Control the frequency generated by the function generator;

b) Control the waveform of the output signal;

c) Measure the output frequency or measure the external input frequency and display it;

d) Measure the amplitude of the output signal and display it;

e) Control the output of a single pulse.

Let's take an example and use the schematic diagram of a power-adaptive square wave generator to explain it in detail. The figure below is a square wave generator that does not require a power supply and can be used as a simple signal source for electronics enthusiasts and laboratories.

This circuit is an adaptive square wave generator composed of six inverters CD4096. The square wave generator circuit is simple and easy to make, so it can be used as a 50Hz square wave generator powered by the mains. When making it, the 220V sine wave of the mains should be isolated and stepped down by a transformer (1~0.75V) before being input to the input end of the circuit to ensure safety.

【Circuit analysis is as follows】

(1) When a small sine wave is input at the input end, the signal is transmitted in two paths. One path is the C1, D1, D2, C2 loop, which completes the rectification and voltage doubling function and provides working power for CD4096.

(2) The other path is coupled by capacitor C3 and enters the input end of an inverter of CD4096 to complete the signal amplification function (the inverter can be used as an amplifier when working with small signals). The amplified signal is processed by the gate circuit of the subsequent stage, converted into a square wave and output through pins 12, 8, and 10 of CD4096. R2 at the output end is an adjustable resistor to ensure that the output end signal is adjustable from 0 to 1.25V.

Function signal generators are often used in electronic design and can provide sine waves, square waves, triangle waves, etc. with a certain frequency and period.