Design of phase-locked frequency synthesizer based on integrated phase-locked loop frequency synthesis chip PE3236

Frequency synthesis technology is a modern means of generating frequency sources. It has been widely used in communications, navigation, Electronic reconnaissance, interference and anti-interference, remote control and telemetry, and modern instrumentation. The rapid development of wireless communication technology has made the role of frequency synthesis technology in communication increasingly significant.

Authors: Zhao Yinghui, Yuan Anmin, Qi Yunjun

Frequency synthesis technology is a modern means of generating frequency sources. It has been widely used in communications, navigation, electronic reconnaissance, interference and anti-interference, remote control and telemetry, and modern instrumentation. The rapid development of wireless communication technology has made the role of frequency synthesis technology in communication increasingly significant.

In the past, frequency synthesizers were assembled with discrete components and small-scale integrated circuits, with complex technology, low reliability, high power consumption, large volume, and high cost. With the rapid development of semiconductor technology and integrated circuit technology, many large-scale integrated circuits for frequency synthesis have appeared. In these large-scale integrated circuits, the main components of the frequency synthesizer, such as the reference frequency divider, the program frequency divider, the phase detector, the lock indicator, and even the microprocessor, are integrated on the same chip. Coupled with a reference oscillator, a voltage-controlled oscillator, a loop filter and a high-speed prescaler, a complete frequency synthesizer can be formed. This greatly reduces the cost, volume, and power consumption of the frequency synthesizer, simplifies the complexity of design and production debugging, and significantly improves the reliability. The appearance of large-scale integrated phase-locked loop frequency synthesizer circuits has opened up a broad prospect for the application of frequency synthesizers.

1 Frequency synthesizer design

The designed frequency synthesizer requires low phase noise, an output frequency of 800 to 1 000 MHz, and a total of 88 channels. The channel selection is performed through the frequency control word sent by the single-chip microcomputer. On the basis of comparing the performance of various large-scale integrated frequency synthesis chips, a single-chip large-scale integrated phase-locked loop frequency synthesis chip PE3236 is selected as the core circuit to form a phase-locked frequency synthesizer.

1.1 Integrated phase-locked loop frequency synthesis chip PE3236

The integrated phase-locked loop frequency synthesis chip PE3236 is a high-performance integer frequency division PLL chip produced by Peregrine Company, the highest frequency division frequency can reach 2.2 GHz. PE3236 uses UTSiCMOS technology and has excellent performance of ultra-low phase noise, making it an ideal choice for cellular network/PCS base stations and wireless local loop base stations.

PE3236 is composed of high-speed prescaler, counter, phase detector and control logic. The high-speed prescaler adopts swallow pulse frequency division technology, and the mode selection determines whether the VCO output frequency ÷ 10 or ÷ 11; the main counter M and the reference counter R divide the dual-mode prescaler output frequency and reference frequency respectively Frequency; Auxiliary counter A is used for the mode selection control logic; the phase detector generates up and down frequency control signals; it also has phase detection frequency detection and clock detection pins. The count value of each counter can be realized through serial or parallel interface programming, or directly through wiring. The chip has the advantages of low power consumption, low phase noise, small spurs, high frequency division, and flexible and convenient programming.

The output frequency fp of the main counter and the output frequency fc of the reference counter are the phase discrimination frequency. The relationship between them and the input frequency and reference frequency is:

fp=fin/[10×(M+1)+A]A≤M+1, M≠0
fc=fr/(R+1) R≥0
When the loop is locked, it should have: fp=fc.

Therefore, the relationship between the input frequency fin of the chip and the reference frequency fr is:

Design of phase-locked frequency synthesizer based on integrated phase-locked loop frequency synthesis chip PE3236

1.2 Design of frequency synthesizer

The designed frequency synthesizer system realization block diagram is shown as in Fig. 1.

Design of phase-locked frequency synthesizer based on integrated phase-locked loop frequency synthesis chip PE3236

Through the serial port, the frequency control word from the single-chip microcomputer sets the internal frequency divider of the integrated phase-locked chip PE3236, the required frequency fo is divided by 10×(M+1) times as a phase discrimination input, and the reference frequency fr is (R+1) Frequency division is used as another phase detection input. After passing the phase detector, the output PD_U and PD_D- reflecting the error of the two phase detection signals are obtained. PD_U and PD_D pass through the loop filter to suppress interference such as noise and spurious After obtaining the control voltage of the VCO, control the work of the VCO so that the output frequency of the VCO is locked at fo (fo =[10×)tochangethecontroldataofthesingle-chipmicrocomputeranddifferentchannelscanbeselected

Design of phase-locked frequency synthesizer based on integrated phase-locked loop frequency synthesis chip PE3236

1.3 Analysis of the influence of loop filter on phase noise performance

With the improvement of radio communication system performance, the requirement of signal source phase noise is often the restricting factor of the whole system. There are many factors influencing the phase noise of the frequency synthesizer, here is a brief analysis of the influence of the loop filter.

In the phase-locked loop frequency synthesizer, the design of the loop filter is very important. Within the loop bandwidth, the phase detector forces the voltage-controlled oscillator (VCO) to track the reference frequency and map the phase noise of the reference oscillator to the VCO. This process is dominated by the phase detector noise floor, because the phase detector noise floor is usually higher than the phase noise of the reference oscillator. Since the compensation frequency is higher than the loop bandwidth, the loop cannot track the reference frequency well, and the total phase noise is equal to the phase noise of the VCO. Therefore, the loop bandwidth should be set at the noise floor of the phase detector and the phase noise when the VCO is freely oscillating. On the intersection. Although the loop bandwidth that is too wide and too narrow can improve the phase noise of the VCO to a certain extent, it cannot improve the phase noise performance of the PLL very well.

In this design, the loop filter is an active proportional-integral filter composed of a precision operational amplifier OP27, as shown in Figure 2. In order to well reduce the PLL phase noise, it is very necessary to select the appropriate loop component values.

Design of phase-locked frequency synthesizer based on integrated phase-locked loop frequency synthesis chip PE3236

2 Test results

On the basis of the above design, an L-band frequency synthesizer was made, and the measured results are as follows:

Working frequency: 800~1 000 MHz, 88 channels. Frequency stability: ±1×10-6.
Output power: ≥ +7 dBm.
Phase noise: ≤ -90 dB (10 kHz away from the center frequency).

3 Conclusion

With the development of radar, electronic countermeasures, aerospace, communications and related technologies, the requirements for frequency synthesis technology have become more stringent. The advantages of integrated phase-locked loop frequency synthesizers, such as small size, low power consumption, low cost, complete functions, high flexibility, and suitable for mass production, have attracted more and more attention. In this paper, a large-scale integrated phase-locked loop frequency synthesis chip PE3236 is used to design and fabricate an L-band frequency synthesizer. The frequency synthesizer has been successfully used in the field tester of decimeter wave instrument landing equipment, and it works well.

The Links:   NL2432HC17-01 1MBI50L-060

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