Sinusoidal signal generator: Sinusoidal signal is mainly used to measure frequency characteristics, nonlinear distortion, gain and sensitivity of circuits and systems. According to the frequency coverage, it is divided into low-frequency signal generator, high-frequency signal generator and microwave signal generator; According to the adjustable range and stability of output level, it can be divided into simple signal generator (signal source), standard signal generator (output power can be accurately attenuated to below-100 dB MW) and power signal generator (output power is more than tens of MW). According to the way of frequency change, it can be divided into tuning signal generator, sweeping signal generator, program-controlled signal generator and frequency synthesis signal generator. Multi-waveform signal generator based on 555

Low frequency signal generator: sine wave generator including audio (200 ~ 20000 Hz) and video (1 Hz ~ 10 MHz). The main vibration stage generally adopts RC oscillator or difference frequency oscillator. In order to test the frequency characteristics of the system, it is required that the output amplitude-frequency characteristics are flat and the waveform distortion is small. High frequency signal generator: high frequency signal generator with frequency of 100 kHz ~ 30 MHz and VHF signal generator with frequency of 30 ~ 300 MHz. Generally, LC tuned oscillator is used, and the frequency can be read out through the dial of tuning capacitor. The main purpose is to measure the technical indicators of various receivers. The output signal can be amplitude modulated or frequency modulated by internal or external low-frequency sinusoidal signals, so that the output carrier frequency voltage can be attenuated below 1 microvolt. The output signal level of (Figure 1) can be accurately read, and the added amplitude modulation or frequency offset can also be read with an electric meter. In addition, the instrument has good shielding to prevent signal leakage. Standard signal generator microwave signal generator: signal generator from decimeter wave to millimeter wave band. The signal is usually generated by UHF triode and distributed parameter resonator reflection klystron, but it tends to be gradually replaced by microwave transistor, field effect transistor, Gunn diode and other solid devices. Generally speaking, the frequency of musical instruments is changed by mechanically tuning the resonant cavity. Each instrument can cover about an octave, and the signal power coupled out of the cavity can generally reach more than 10 MW. The simple signal source only needs to add 1000 Hz square wave amplitude modulation, while the standard signal generator can adjust the output reference level to 1 MW, and then read the decibel MW value of the signal level from the subsequent attenuator; There must also be internal or external rectangular pulse amplitude modulation to test the receiver, such as radar. Sweep frequency and program-controlled signal generator: The sweep frequency signal generator can generate signals with constant amplitude and linear frequency change in a limited range. In high frequency and very high frequency band, the low frequency scanning voltage or current is used to control the oscillation circuit elements (such as varactor diode or magnetic core coil) to realize swept frequency oscillation; In the early stage of microwave section, voltage tuning frequency is adopted, and the oscillation frequency is changed by changing the DC voltage of the spiral electrode of the backward wave tube. Later, magnetic tuning frequency sweep was widely used, YIG ferrite beads were used as the tuning loop of microwave solid-state oscillator, and the DC magnetic field was controlled by scanning current to change the resonance frequency of the beads. The frequency sweep signal generator includes automatic frequency sweep, manual control, program control and remote control. Standard signal generator

Frequency synthesis signal generator: The signal of this kind of generator is not directly generated by an oscillator, but takes a high-stability timely oscillator as a standard frequency source, and uses frequency synthesis technology to form a signal with any required frequency, which has the same frequency accuracy and stability as the standard frequency source. The output signal frequency can usually be selected according to the decimal places, and the highest resolution can reach 1 1 digits. In addition to manual selection, the frequency can be programmed and remotely controlled, and it can also be swept step by step, which is suitable for automatic test system. The direct frequency synthesizer consists of crystal oscillation, addition, multiplication, filtering and amplification circuits. The frequency conversion is rapid but the circuit is complex, and the highest output frequency can only reach about 1000 MHz. The widely used indirect frequency synthesizer uses a standard frequency source to control an electrically tuned oscillator through a phase-locked loop (frequency doubling, frequency division and frequency mixing can be realized at the same time in the loop), thus generating and outputting signals of various required frequencies. The highest frequency of the synthesizer can reach 26.5 GHz. The frequency synthesizer with high stability and high resolution has many modulation functions (amplitude modulation, frequency modulation and phase modulation), plus amplification, amplitude stabilization and attenuation circuits, which constitutes a new type of high performance and programmable synthetic signal generator, and can also be used as a phase-locked sweep generator. Function generator: Also called waveform generator. It can generate some specific periodic time function waveforms (mainly sine wave, square wave, triangle wave, sawtooth wave, pulse wave, etc. ). The frequency range can be from several millihertz or even several megahertz to tens of megahertz. Besides testing communication, instruments and automatic control systems, it is also widely used in other non-electric measurement fields. Fig. 2 is one of the methods for generating the above waveform. The integrator is connected with a certain threshold switching circuit with hysteresis characteristics (such as Schmidt trigger) to form a loop, and the integrator can integrate square waves into triangular waves. Schmidt circuit can make triangular wave jump to form square wave when it rises to a certain threshold or falls to another threshold. The frequency can change with the change of RC value in the integrator, and the two thresholds can be controlled by the applied voltage. Sine waves can be formed by adding triangular waves to a shaping network composed of many different bias diodes to form many broken lines with different slopes. The other way is to use a frequency synthesizer to generate a sine wave, then amplify and limit it several times to form a square wave, and then integrate the square wave into a triangular wave and a sawtooth wave with positive and negative slopes. The frequency of these function generators can be controlled, programmed, locked and scanned. In addition to working in continuous wave state, the instrument can also work by keying, gating or triggering. Pulse signal generator: a generator that generates rectangular pulses with adjustable width, amplitude and repetition frequency, which can be used to test the transient response of linear systems or to test the performance of pulse digital systems such as radar and multi-channel communication with analog signals. The pulse generator is mainly composed of a master oscillator, a delay stage, a pulse forming stage, an output stage and an attenuator. The master oscillator is usually a circuit such as a multivibrator, which mainly works in trigger mode except for self-excited oscillation. Usually, a pre-trigger pulse is output after the trigger signal is applied to trigger the oscilloscope and other observation instruments in advance, and then the main signal pulse is output after an adjustable delay time, and its width is adjustable. Some can output pairs of main pulses, and some can output main pulses with different delays in two ways. Random signal generator: Random signal generators are divided into noise signal generators and pseudo-random signal generators. Noise signal generator: a completely random signal is white noise with a uniform spectrum in the working frequency band. Commonly used white noise generators mainly include: saturated diode white noise generator working in coaxial line system below 1000 MHz; Gas discharge tube type white noise generator for microwave waveguide system: solid-state noise source (which can work in the full frequency band below 18 GHz) using the noise in the reverse current of crystal diode, etc. The intensity of the output of the noise generator must be known, which is usually expressed by the number of decibels (called the super-noise ratio) in which its output noise power exceeds the thermal noise of resistance or by its noise temperature. The main purposes of the noise signal generator are: ① to introduce a random signal into the system under test to simulate the noise under actual working conditions and determine the performance of the system; ② Add a known noise signal and compare it with the internal noise of the system to determine the noise coefficient; ③ Using random signals instead of sine or pulse signals to test the dynamic characteristics of the system. For example, the impulse response function of the network can be obtained by measuring the cross-correlation function between the output signal and the input signal of the network with white noise as the input signal. Pseudo-random signal generator: when measuring correlation function with white noise signal, if the average measurement time is not long enough, there will be statistical error, which can be solved with pseudo-random signal. When the pulse width of binary coded signal is small enough and the number of bits n in a code period is large, the amplitude of signal spectrum is uniform in the frequency band below fb= 1/ bit, which is called pseudo-random signal. As long as the measurement time is equal to an integer multiple of the period of the coded signal, no statistical error will be introduced. Binary signals can also provide the time delay required for correlation measurement. The pseudo-random coded signal generator consists of n-level shift registers with feedback loops, and the generated code length is n = 2- 1.

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Signal generator, also known as signal source or oscillator, is widely used in production practice and scientific and technological fields. Various waveform curves can be expressed by trigonometric function equations. A circuit that can generate various waveforms such as triangular wave, sawtooth wave, rectangular wave (including square wave) and sine wave is called a function signal generator. Function signal generators are widely used in circuit experiments and equipment testing. For example, in communication, broadcasting and television systems, radio frequency (high frequency) emission is needed, and the radio frequency wave here is the carrier wave. In order to execute audio (low frequency), video signal or pulse signal, an oscillator capable of generating high frequency is needed. In industry, agriculture, biomedicine and other fields, such as high-frequency induction heating, melting, quenching, ultrasonic diagnosis, nuclear magnetic resonance imaging and so on. An oscillator with high or low power and high or low frequency is needed.