CN109104187B - Full-digital broadband frequency synthesizer - Google Patents

Abstract

The invention sets the programmable logic controller in the circuit of the frequency synthesizer, and can adjust the parameters of the loop filter according to the actual input signal condition of the frequency synthesizer, thereby enriching the function and adaptability of the traditional frequency synthesizer. Secondly, the present invention also sets a phase/frequency decider to decide the phase and frequency of the input signal, which can avoid arithmetic operation and code conversion, and effectively reduce the complexity and power consumption of the circuit.

Description

An all-digital broadband frequency synthesizer

technical field

The invention relates to a frequency synthesizer, in particular to an all-digital wideband frequency synthesizer.

Background technique

Bandwidth is a sign that UWB radar is different from narrowband radar. Compared with narrowband radar, UWB radar can provide more target information, and it can also carry out more effective target recognition. With the advancement of radar signal processing technology, the bandwidth of the video signal that can be processed is getting wider and wider, so that the original operating frequency and bandwidth of the radar frequency synthesizer can no longer meet the technical requirements of ultra-wideband active phased array radar.

Frequency synthesizers are key components in modern communication systems, radars, and test equipment, which can provide high-precision and high-stability frequencies. Since the concept of frequency synthesis was first proposed in the 1930s, three basic frequency synthesis methods have been formed: (1) direct frequency synthesis; (2) phase-locked frequency synthesis; (3) direct digital frequency synthesis (DDS). Early frequency synthesizers use direct frequency synthesis, which is simple in structure and easy to implement, but large in size and high in cost.

A frequency synthesizer is proposed in the patent document CN201320570307.6. The frequency hopping of the present invention adopts the DDS excitation PLL method to realize the frequency synthesis scheme, and the low frequency frequency adopts the DDS direct generation method, which fully reflects the flexibility and portability of the software radio, and the frequency synthesizer has a fast locking time, and Guaranteed small spurious, accurate frequency accuracy, low noise, excellent spectral purity and wide frequency hopping range, reaching high technical indicators. However, in the device of the invention, the circuit structure is fixed and rigid, the flexibility is not enough, and the expandability is not enough, so it cannot be adjusted according to different actual needs.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and to provide a frequency synthesizer with a novel structure and ingenious conception, which can flexibly set various attributes of the frequency synthesizer as required through a programmable logic control module and a phase judgment module, Further, the functions and adaptability of the traditional frequency synthesizer are enriched, and the flexibility and tracking performance of the frequency synthesizer are greatly improved.

The present invention realizes through the following scheme:

An all-digital broadband frequency synthesizer, which specifically includes: a digital frequency and phase detector, a loop filter, a digital voltage-controlled oscillator, a digital frequency divider, a loop parameter controller, a phase/frequency decider, a programmable Logic controller; the output of the digital frequency discriminator is connected with the phase/frequency decider, the phase/frequency decider is respectively connected with the loop filter and the programmable logic controller, and the loop filter is connected with the digital voltage controlled oscillator , the output of the voltage-controlled vibrator is connected with the frequency divider, and the output of the frequency divider is used as an input signal of the digital frequency and phase detector; at the same time, the digital programmable logic controller is connected with the loop parameter controller, and the loop parameter The controller is connected to the loop filter.

Further, the digital frequency and phase detector compares the input reference signal and the output of the frequency divider with frequency and phase, and then obtains a signal representing the phase/frequency error to the phase/frequency decider; the phase/frequency decider is based on The error signal is progressively judged, and the judgment results of phase and frequency are obtained, and sent to the loop filter and the programmable logic controller respectively; the programmable logic controller performs the loop filter according to the judgment results of the phase/frequency decider. The parameters are adjusted, and the adjusted result is sent to the loop parameter controller, and the loop parameter controller controls the loop filter according to the result.

Further, a tunable resistor is provided in the loop filter, and the loop parameter controller adjusts the performance of the loop filter by adjusting the tunable resistor in the loop filter.

Further, the digital frequency discriminator and phase discriminator includes a clock prescaler module, a multi-bit counter module, a multi-bit register module, and an edge detection module, and the clock prescaler module receives the clock signal input by the fixed crystal oscillator clock, and then passes through even numbers, Odd and half-integer cascade frequency division to output the reference clock signal, and then output the reference clock signal to the edge detection module and the multi-bit counter module, the edge detection receives the feedback clock signal, and then detects the edge of the reference clock signal and the feedback clock signal, according to The edge cases of the two give the signal of the phase/frequency error.

Further, the circuit of the phase/frequency decider specifically includes four NOR gates and two D-type flip-flops.

Further, the phase/frequency decider includes two logic circuits, and the two logic circuits include two NOR gate circuits, wherein an input end of the NOR gate receives the positive and negative error signals output by the digital frequency discriminator , the other input terminal receives a decision clock to determine the decision cycle of the phase/frequency decision; the output terminal of the logic circuit is used as the input terminal of the D-type flip-flop, and the other input terminal of the D-type flip-flop is connected to the decision clock signal, The D-type flip-flop outputs high and low levels to obtain the signal after tracking compensation.

Further, the programmable logic controller may be Siemens S7-200 or Mitsubishi FX2N or ABB's AC500.

Further, the frequency synthesizer can be applied to airborne radar, vehicle radar, aviation radar and satellite radar.

Further, the digital frequency divider may be an even frequency divider, an odd frequency divider, or a fractional frequency divider.

Compared with the prior art, the present invention has the following beneficial effects:

First of all, the present invention sets a programmable logic controller in the circuit of the frequency synthesizer, which can adjust the parameters of the loop filter according to the actual input signal of the frequency synthesizer, thereby enriching the functions and adaptability of the traditional frequency synthesizer. .

Secondly, the present invention also sets a phase/frequency decider to decide the phase and frequency of the input signal, which can avoid arithmetic operation and code conversion, and effectively reduce the complexity and power consumption of the circuit.

Finally, the frequency synthesizer provided by the present invention is flexible in structure, low in complexity, low in power consumption, fully digitally processed, and has broad application advantages and economic prospects.

Description of drawings

Fig. 1 is the circuit structure diagram of the frequency synthesizer of the present invention.

FIG. 2 is a circuit structure diagram of a digital frequency and phase detector in the frequency synthesizer of the present invention.

Fig. 3 is the circuit structure diagram of the phase/frequency decider in the frequency synthesizer of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. These drawings are all simplified schematic diagrams, and only illustrate the basic structure of the present invention in a schematic manner, so they only show the structures related to the present invention.

With the continuous development of communication, digital television, satellite positioning, aerospace and remote control telemetry, the requirements for frequency stability, spectral purity, frequency range and output frequency of frequency sources are getting higher and higher. In order to improve the frequency stability, methods such as crystal oscillators are often used to solve the problem, but it cannot meet the requirement of a large number of frequencies. Therefore, a large number of frequency synthesis techniques are currently used. By adding, subtracting, multiplying and dividing the frequency, a large number of different frequencies with the same stability and accuracy can be generated from a standard frequency source with high stability and accuracy. A frequency synthesizer is a device that generates multiple frequencies from one or more reference frequencies. It is an indispensable key circuit in modern communication systems, and is widely used in digital communication, satellite communication, radar, navigation, aerospace, remote control telemetry and high-speed instrumentation and other fields. The information industry represented by communications is the fastest growing industry in contemporary times. Therefore, frequency synthesizers have also developed rapidly, forming a complete series of varieties, and the market demand is also particularly large.

The technical complexity of frequency synthesizer is very high, and it has gone through three development stages: direct synthesis analog frequency synthesizer, phase-locked frequency synthesizer, and direct digital frequency synthesizer. Among them, the phase-locked frequency synthesizer and the direct digital frequency synthesizer have received attention from all walks of life and have developed rapidly.

Based on the current development trend and technical requirements, the present invention proposes a frequency synthesizer with a simple structure and rich functions. The present invention will be described below with reference to specific embodiments.

Example 1:

Figure 1 shows the circuit structure diagram of the frequency synthesizer of the present invention, specifically: a digital frequency and phase detector, a loop filter, a digital voltage-controlled oscillator, a digital frequency divider, a loop parameter controller, a phase /Frequency decider, programmable logic controller; the output of the digital frequency discriminator is connected to the phase/frequency decider, and the phase/frequency decider is connected to the loop filter and the programmable logic controller respectively. The loop filter It is connected with the digital voltage-controlled oscillator, the output of the voltage-controlled oscillator is connected with the frequency divider, and the output of the frequency divider is used as an input signal of the digital frequency and phase detector; at the same time, the digital programmable logic controller and the loop parameter controller connected, the loop parameter controller is connected with the loop filter.

In the present invention, the related digital phase detector, digital voltage-controlled oscillator, and digital frequency divider have the characteristics of high resolution, high linearity, and high complexity, so as to improve the signal processing performance and accuracy, and increase the The phase/frequency decider can avoid arithmetic operations and code conversion, significantly reducing the complexity and power consumption of the circuit structure.

Further, the digital frequency discriminator compares the frequency and phase of the input reference signal and the output of the frequency divider, and then obtains a signal representing the phase/frequency error to the phase/frequency decider; the phase/frequency decider is based on the error signal. Progressive judgment, the judgment results of phase and frequency are obtained, and sent to the loop filter and the programmable logic controller respectively; the programmable logic controller adjusts the parameters of the loop filter according to the judgment results of the phase/frequency decider , and send the adjusted result to the loop parameter controller, and the loop parameter controller controls the loop filter according to the result.

Further, a tunable resistor is provided in the loop filter, and the loop parameter controller adjusts the performance of the loop filter by adjusting the tunable resistor in the loop filter.

For different signals to be processed, the bandwidth coverage may be very large. For traditional frequency synthesizers, the bandwidth that can be processed is often limited by the performance of the ring filter, and simply expanding the ring On the one hand, the processing range of the filter will increase the cost of the ring filter, and it will also reduce the processing accuracy of the ring filter. In the present invention, by adding a programmable logic controller to the circuit, the programmable logic controller receives The input signal of the loop filter is used to adjust the loop filter in real time according to the signal to be processed, which can expand the processing bandwidth range of the loop filter and improve the flexibility of the synthesis filter.

Fig. 2 shows the circuit structure of the digital frequency and phase detector used in the present invention, which specifically includes a clock prescaler module, a multi-bit counter module, a multi-bit register module, and an edge detection module. At the same time, the clock prescaler module receives Fix the clock signal input by the crystal oscillator clock, and then output the reference clock signal through even, odd, and half-integer cascade frequency division, and then output the reference clock signal to the edge detection module and the multi-bit counter module. The edge detection receives the feedback clock signal, and then Detect the edge of the reference clock signal and the feedback clock signal, and obtain the phase/frequency error signal according to the edge conditions of the two.

For the digital frequency discriminator, the selection of the reference clock signal is very important. The multi-bit counting clock input with fixed duty cycle is obtained by cascading the frequency division of the fixed clock. This improves the control accuracy and reduces the difficulty of implementation.

At the same time, in the digital frequency and phase detector of the present invention, an edge detection module is also set to detect the edge of the reference clock and the feedback clock, when the frequency is not locked, the frequency difference is counted, and the frequency difference digital quantity is output; when the frequency is locked , count the phase difference, and complete the update of the linear phase difference digital quantity on the rising edge of each reference clock.

FIG. 3 shows the circuit structure of the phase/frequency decider used in the present invention, and the circuit specifically includes four NOR gates and two D-type flip-flops.

Further, the phase/frequency decider includes two logic circuits 1 and 2, and the two logic circuits include two NOR gate circuits, wherein one input end of the NOR gate receives the positive and negative errors output by the digital frequency discriminator. signal, the other input terminal receives a decision clock to determine the decision cycle of the phase/frequency decision; the output terminal of the logic circuit is used as the input terminal of the D-type flip-flop, and the other input terminal of the D-type flip-flop is connected to the decision clock signal, D The type flip-flop outputs high and low levels to obtain the signal after tracking compensation.

Specifically, the two logic circuits will be reset by the decision clock signal after each decision to ensure stable output at the beginning of each clock cycle. When there is no falling signal in the next update cycle time, logic circuit 1 remains high. , and when the decision clock signal reaches the rising edge, the decision circuit outputs a high level with a rising frequency/phase; and if there is only a falling signal within the update cycle time, the decision circuit finally outputs a high level with a falling frequency/phase.

If the update cycle of the decision circuit needs to be changed, the update cycle can be modified only by changing the frequency division ratio of the circuit. This design can effectively reduce the complexity of the circuit, and can work in any update cycle, which is convenient, flexible, accurate and efficient.

At the same time, specifically, considering the three aspects of cost, quality and performance, the programmable logic controller can be selected from three models of Siemens S7-200, Mitsubishi FX2N or ABB's AC500.

Further, the frequency synthesizer can be applied to airborne radar, vehicle radar, aviation radar and satellite radar.

Further, the digital frequency divider may be an even frequency divider, an odd frequency divider, or a fractional frequency divider.

The embodiments of the present invention have been described above, but those skilled in the art should understand that these are only examples, and those skilled in the art can make various changes to the embodiments without departing from the principles and essence of the present invention. or modification, but these changes and modifications all fall into the protection scope of the present invention.

Claims (7)

1. an all-digital broadband frequency synthesizer, is characterized in that comprising: digital frequency and phase detector, loop filter, digital voltage-controlled oscillator, digital frequency divider, loop parameter controller, phase/frequency decision device , programmable logic controller; wherein, the phase/frequency decision device includes a D-type flip-flop and two logic circuits, the two logic circuits include two NOR gate circuits in total; the output of the digital frequency discriminator It is connected with the phase/frequency decider, one of the input terminals of the two NOR gate circuits receives the positive and negative error signals output by the digital frequency discriminator, and the other input terminal receives a decision clock to determine the phase/frequency decision The output of the logic circuit is used as the input of the D-type flip-flop, the other input of the D-type flip-flop is connected to the judgment clock signal, and the D-type flip-flop outputs a high level or a low level to track the signal Compensation; the phase/frequency decider is connected with the loop filter and the programmable logic controller respectively, the loop filter is connected with the digital voltage-controlled oscillator, the output of the digital voltage-controlled oscillator is connected with the digital frequency divider, the digital frequency division The output of the device is used as an input signal of the digital frequency and phase detector; meanwhile, the programmable logic controller is connected with the loop parameter controller, and the loop parameter controller is connected with the loop filter. 2. frequency synthesizer according to claim 1, is characterized in that: described digital frequency discriminator phase discriminator carries out the comparison of frequency and phase to the output of input reference signal and digital frequency divider, then obtains a representative phase/frequency The error signal is sent to the phase/frequency decider; the phase/frequency decider makes a progressive decision according to the error signal, and obtains the decision results of phase and frequency, and sends them to the loop filter and programmable logic controller respectively; programmable logic controller According to the decision result of the phase/frequency decider, the parameters of the loop filter are adjusted, and the adjusted result is sent to the loop parameter controller, and the loop parameter controller controls the loop filter according to the result. 3. The frequency synthesizer according to claim 2, characterized in that: the loop filter is provided with a tunable resistance, and the loop parameter controller is adjusted by adjusting the tunable resistance in the loop filter performance of the loop filter. 4. frequency synthesizer according to claim 1, is characterized in that: described digital frequency discrimination phase discriminator comprises clock prescaler module, multi-bit counter module, multi-bit register module, edge detection module, and clock prescaler simultaneously The frequency module receives the clock signal input by the fixed crystal oscillator clock, and then outputs the reference clock signal through even, odd, and half-integer cascade frequency division, and then outputs the reference clock signal to the edge detection module and the multi-bit counter module, and the edge detection receives the feedback clock Then, the edges of the reference clock signal and the feedback clock signal are detected, and the signal of the phase/frequency error is obtained according to the edge conditions of the two. 5 . The frequency synthesizer according to claim 1 , wherein the programmable logic controller can be Siemens S7-200 or Mitsubishi FX2N or AC500 of ABB. 6 . 6. The frequency synthesizer according to claim 1, wherein the frequency synthesizer can be applied to airborne radar, vehicle radar, aviation radar and satellite radar. 7. The frequency synthesizer according to claim 1, wherein the digital frequency divider can be an even frequency divider, an odd frequency divider, or a fractional frequency divider.

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