1. 1 Development Status and Research Survey of Digital Frequency Meter

With the rapid development of electronic technology, various discrete electronic components and their related functional units are gradually replaced by integrated chips with more powerful functions, more stable performance and more convenient use. Various automatic control, automatic measurement and automatic display circuits composed of integrated chips and some peripheral circuits are distributed in various electronic products and equipment. Digital systems and digital equipment have been widely used in various fields, and the speed of upgrading is changing with each passing day.

In the very wide application field of electronic systems, digital circuits for processing discrete information can be seen everywhere. Digital technology is used to design consumer microwave ovens and televisions, advanced industrial control systems, space communication systems, traffic control radar systems, hospital emergency systems, etc. With the development of digital circuit manufacturing industry, system designers can achieve more functions in a smaller space, thus improving the reliability and speed of the system.

Digital frequency meter is an indispensable measuring instrument in modern communication measuring equipment system. It not only requires the circuit to generate signals with accurate frequency and high stability, but also requires that the frequency can be changed conveniently.

The main realization methods of digital frequency meter are direct, phase-locked, direct digital and hybrid.

The advantages of direct mode are high speed and low phase noise, but its structure is complex and there are many spurs, so it is generally only used for ground radar.

The advantages of phase locking are automatic control of phase synchronization, high production frequency, low power consumption and easy realization of serialization, miniaturization, modularization and engineering.

The advantages of direct digitization are circuit stability, high precision, easy serialization, miniaturization, modularization and engineering.

With the development of single-chip phase-locked digital frequency meter, phase-locked and digital are easy to realize serialization, miniaturization, modularization and engineering, and their performance is getting better and better. They have gradually become the two most typical and widely used digital frequency meters.

1.2 Research background and main research significance of this topic.

Digital frequency meter is an indispensable measuring instrument in the fields of computer, communication equipment, audio and video. And it is closely related to many measurement schemes and results of electrical parameters, so frequency measurement is more important. In digital circuit, frequency meter belongs to sequential circuit, which is mainly composed of flip-flops with memory function. It has been widely used in computers and various digital instruments. Among CMOS circuit series products, frequency meter is the most widely used and varied product.

This topic adopts direct digital frequency meter, which has simple design principle, full hardware circuit realization, stable circuit and high precision, and greatly shortens the production cycle.

1.3 main research contents of this topic

In this paper, a digital frequency meter of 1 Hz- 1 MHz is made by digital circuit, and the required frequency is displayed by digital tube. Digital frequency meter is mainly composed of four parts: time base circuit, gate circuit, logic control circuit and controllable counting, decoding and display circuit. The principle block diagram is shown in figure 1- 1:

Figure 1- 1 principle block diagram