CN220964875U - Broadband DDS spread spectrum device - Google Patents

Abstract

The utility model discloses a broadband DDS spread spectrum device, which comprises a DDS generating circuit, a frequency doubling circuit and a multi-stage spread spectrum circuit, wherein the DDS generating circuit generates an intermediate frequency signal, the frequency doubling circuit divides the intermediate frequency signal into two paths, the two paths are respectively input into a first low-pass filtering branch and a second frequency doubling branch, the spread spectrum circuit of each stage is provided with a second low-pass filtering branch, a local oscillation signal input end, a local oscillation circuit and a spread spectrum branch, the radio frequency signal input end of the spread spectrum circuit divides a received frequency band signal into two paths, the two paths are respectively connected into the second low-pass filtering circuit and the spread spectrum branch, and one of signals output by the second low-pass filtering circuit and the spread spectrum branch is selected as a spread spectrum signal output by the spread spectrum circuit. The device can realize rapid frequency hopping, spectrum purity and rapid sweep frequency test of broadband signals.

Description

Broadband DDS spread spectrum device

Technical Field

The utility model relates to the technical field of radio frequency signal processing, in particular to a broadband DDS spread spectrum device which can realize a 0-14GHz fast frequency hopping comprehensive source.

Background

DDS (direct digital frequency synthesizer, DIRECT DIGITAL SYNTHESIS) is a common microwave component in certain applications, such as signal sources, spectrometers and other instrumentation fields. The DDS technology has the advantages of high frequency point switching speed, high frequency resolution and the like. The disadvantage is that the output frequency is high-end limited.

When DDS is selected as the frequency source, there are several ways to perform frequency expansion.

(1) The frequency is extended by direct frequency multiplication. The method can realize rapid frequency hopping, and has simple circuit structure. The disadvantage is that direct frequency doubling can lead to a 20log degradation of the DDS phase noise and near-end spurious index. Near-end spurious emissions of the DDS cannot be effectively filtered out, affecting the output frequency spectrum purity.

(2) The frequency is extended by direct excitation PLL method using DDS. The DDS output bandwidth needs to be greater than the ratio of the DDS center frequency to the minimum divider ratio to allow continuous frequency coverage of the synthesizer.

(3) The frequency is extended by adopting a DDS and PLL in-loop mixing method. The method has the advantages that the DDS is utilized to expand the output frequency of the phase-locked loop, the defect of low resolution of the output frequency of the PLL is overcome, and the small stepping frequency is output. By using the down mixing mode, the feedback frequency is reduced, the in-loop frequency division ratio is reduced, and in-loop phase noise is improved. The disadvantage is that when the DDS output frequency is close to the integral multiple of the phase discrimination frequency, the nonlinearity of the output spurious pass through the mixer falls near the phase discrimination frequency, can not be effectively filtered by the loop filter, and seriously affects the output frequency spectrum purity.

(4) The frequency is extended by using a DDS and PLL out-of-loop mixing method. The phase demodulation frequency of the PLL can be made higher, the frequency division times in the loop are greatly reduced, and the frequency conversion time is shorter. The phase noise of the PLL output signal is relatively good. The disadvantage is that the non-linearity of the mixer mixes the spurs of the DDS into the output frequency range and that the non-linearity spurs of the mixer itself also affects the spectral purity of the output frequency.

(5) The frequency is spread using an in-loop insertion frequency synthesizer approach. The loop frequency division ratio M value can be designed to be lower, and the output phase noise of the PLL is reduced; the loop lock time is short, which shortens the frequency conversion time. When a fixed P frequency divider is used, the frequency synthesizer will have a 20lg (P) dB degradation of the phase modulated spurs in the spurs generated by the DDS within the phase locked loop bandwidth.

Disclosure of utility model

The technical purpose is that: aiming at the technical problems, the utility model provides a broadband DDS spread spectrum device which can realize rapid frequency hopping, spectrum purity and rapid sweep frequency test of broadband signals.

The technical scheme is as follows: in order to achieve the technical purpose, the utility model adopts the following technical scheme:

A wideband DDS spreading device, comprising:

The DDS generation circuit comprises a first frequency source (LO-1) and a first DDS for generating an intermediate frequency signal;

The frequency doubling circuit comprises a first low-pass filtering branch and a frequency doubling branch, and is used for dividing the intermediate frequency signal into two paths and respectively inputting the two paths into the first low-pass filtering branch and the frequency doubling branch; the frequency doubling branch performs frequency doubling treatment on the received signals to obtain corresponding frequency band signals; the output ends of the first low-pass filtering branch and the frequency doubling branch are provided with a single-pole double-throw switch which is commonly connected and used for selecting one of the single-pole double-throw switches as the output of the frequency doubling circuit;

The multi-stage spread spectrum circuit is provided with a radio frequency signal input end, a second low-pass filtering branch, a local oscillator circuit, a spread spectrum branch and a spread spectrum signal output end, wherein the radio frequency signal input end of the first-stage spread spectrum circuit receives the frequency band signals output by the frequency doubling circuit, and the radio frequency signal input ends of the other spread spectrum circuits receive the frequency band signals output by the last-stage spread spectrum circuit; the frequency band signal received by the radio frequency signal input end is divided into two paths, the two paths are respectively connected into a second low-pass filter circuit and a spread spectrum branch, the local oscillator circuit is used for providing local oscillator signals for the spread spectrum branch, a mixer used for carrying out mixing processing on the frequency band signal received by the spread spectrum branch and the local oscillator signals is arranged in the spread spectrum branch, and the output ends of the second low-pass filter circuit and the spread spectrum branch are provided with a single-pole double-throw switch which is commonly connected and used for alternatively serving as the output of the spread spectrum circuit.

Preferably, the frequency doubling circuit further comprises a first switch, a second filter and a second switch, wherein the first switch (S1) and the second switch are single-pole double-throw switches, and the second filter is a band-pass filter;

The DDS generating circuit generates a 0-Fa frequency band signal, the first switch and the second filter are used for dividing the 0-Fa frequency band signal into two paths, one path is the 0-Fa frequency band signal, the 0-Fa frequency band signal is input into the first low-pass filtering branch, and the 0-Fa frequency band signal is obtained after low-pass filtering; the other path is Fa/2-Fa frequency band signals, and the Fa/2-Fa frequency band signals are obtained after frequency doubling treatment by inputting a frequency doubling branch; the second switch S2 is configured to select one path from the 0-Fa frequency band signal and the Fa-2Fa frequency band signal as an output of the frequency multiplier circuit.

Preferably, in the frequency doubling circuit, the frequency doubling branch includes a first amplifier, a frequency doubling device, a third filter, a second amplifier and a fourth filter which are connected in series, and the third filter and the fourth filter are bandpass filters with different passbands.

Preferably, each stage of spread spectrum circuit is provided with a first single-pole double-throw switch, a second single-pole double-throw switch, a first single-pole multi-throw switch, a second single-pole multi-throw switch, a third single-pole multi-throw switch and a front band-pass filter;

The radio frequency signal input end divides a received frequency band signal into two paths through a first single-pole double-throw switch and a front band-pass filter, one path is a 0-Fbi frequency band signal, the 0-Fbi frequency band signal is accessed into a second low-pass filter circuit and is subjected to low-pass filtering processing to obtain a 0-Fbi frequency band signal, the other path is a Fbj-Fbi frequency band signal, the signal is input into a spread spectrum branch, b represents a b-stage spread spectrum circuit, 0< Fbj < Fbi, and Fbi represents the maximum frequency of the frequency band signal input by the b-stage spread spectrum circuit;

The local oscillation circuit is provided with a plurality of frequency sources and outputs one path through a first single-pole multi-throw switch as local oscillation signals;

The frequency spreading branch circuit further comprises a plurality of band-pass filter circuits, the mixer is used for carrying out mixing processing on the Fbj-Fbi frequency band signals and the local oscillator signals to obtain Fbi-Fbk frequency band signals, the output end of the mixer inputs signals of different frequency bands to each band-pass filter circuit through a second single-pole multi-throw switch, each band-pass filter circuit has different pass bands and jointly forms a permitted frequency range which is Fbi-Fbk, fbk represents the maximum frequency of spread spectrum signals output by a b-th stage spread spectrum circuit, and the output end of each band-pass filter circuit is jointly connected with a third single-pole multi-throw switch;

The second single-pole double-throw switch is connected with the output end of the third single-pole multi-throw switch and is used for selecting one path from the 0-Fbi frequency band signal and the Fbi-Fbk frequency band signal to serve as the output of the spread spectrum circuit.

Preferably, in the spread spectrum branch, each band-pass filter circuit includes an amplifier, and the input end and the output end of the amplifier are respectively provided with a band-pass filter with the same passband.

Preferably, in the local oscillation circuit, the frequency sources are directly generated by using PLL devices of an integrated VCO, the output ends of the frequency sources (LO-2 to LO-4; LO-5 to LO-8; LO-9 to LO-11) are connected to the input end of the first single-pole multi-throw switch by arranging a single-pole single-throw switch, and an amplifier is arranged between the output end of the first single-pole multi-throw switch and the corresponding mixer.

Preferably, the first low-pass filtering branch and the second low-pass filtering branch are both implemented by low-pass filters.

Preferably, the apparatus comprises three stage spreading circuits, namely a first stage spreading circuit, a second stage spreading circuit and a third stage spreading circuit, wherein,

The DDS generation circuit generates a signal with the frequency range of 0-400 MHz;

In the frequency doubling circuit, the 0-400MHz frequency band signal is divided into two paths, one path is the 0-400MHz frequency band signal, the other path is the 200-400MHz frequency band signal, the 400-800MHz frequency band signal is obtained through the frequency doubling branch, and the frequency doubling circuit outputs the 0-800MHz frequency band signal;

In the first spread spectrum circuit, a frequency band signal received by a radio frequency signal input end is divided into two paths, one path is a frequency band signal of 0-800MHz, and the other path is a frequency band signal of 320-800 MHz; the local oscillation signal comprises three frequency sources with the frequencies of 1600MHz, 2080MHz and 2560MHz respectively; the spread spectrum branch comprises three band-pass filters, the pass bands of which are respectively 800-1280MHz, 1280-1760MHz and 1760-2240 MHz; the first spread spectrum circuit outputs a signal of 0-2240MHz frequency band;

In the second spread spectrum circuit, the frequency band signal received by the radio frequency signal input end is divided into two paths, one path is a 0-2240MHz frequency band signal, and the other path is a 800-1990MHz frequency band signal; the local oscillation signal comprises four frequency sources with frequencies of 4230MHz, 5420MHz, 6610MHz and 7800MHz respectively; the spread spectrum branch comprises four band-pass filters, the pass bands of which are 2240-3430MHz, 3430-4620MHz, 4620-5810MHz and 5810-7000MHz respectively; the second spread spectrum circuit outputs a signal of 0-7000MHz frequency band;

In the third spread spectrum circuit, the frequency band signal received by the radio frequency signal input end is divided into two paths, one path is a 0-7000MHz frequency band signal, and the other path is a 2240-5795MHz frequency band signal; the local oscillation signal comprises three frequency sources with frequencies of 12795MHz, 13955MHz and 16305MHz respectively; the spread spectrum branch circuit comprises three band-pass filters, the pass bands of the three band-pass filters are 7000-9350MHz, 9350-11700MHz and 11700-14000MHz respectively, and the third spread spectrum circuit outputs signals in the frequency band of 0-14000 MHz.

The beneficial effects are that: due to the adoption of the technical scheme, the utility model has the following beneficial effects:

The device uses 1 point frequency source as a DDS clock, uses a multi-point frequency source as a point frequency local oscillator capable of being switched in a multistage spread spectrum mixing process, and meets the frequency hopping time index through switching on and off of the switch, so that the whole spread spectrum device can realize the rapid sweep frequency test of broadband signals, and has a good spurious suppression effect.

Drawings

Fig. 1 is a schematic diagram of a DDS spread spectrum assembly of the present utility model;

FIG. 2 is a schematic diagram of a DDS generation circuit and a frequency doubling circuit;

FIG. 3 is a schematic diagram of a first stage spread spectrum circuit;

FIG. 4 is a schematic diagram of a second stage spread spectrum circuit;

FIG. 5 is a schematic diagram of a third stage spread spectrum circuit;

FIG. 6 is a cross-modulation spurious simulation diagram of a first section of a first mixing selection;

Fig. 7 is a cross-modulation spurious simulation diagram of a first section of second mixing frequency selection;

FIG. 8 is a cross-modulation spurious simulation diagram of a third section of second mixing frequency selection;

Fig. 9 is a cross-modulation spurious simulation diagram of a third mixing frequency selection first segment;

fig. 10 is a cross-modulation spurious simulation diagram of a third mixing frequency-selective second segment;

Fig. 11 is a cross-modulation spurious simulation diagram of a third section of a third mixing frequency selection.

Detailed Description

Embodiments of the present utility model will be described in detail below with reference to the accompanying drawings.

As shown in fig. 1, the present utility model provides a wideband DDS spread spectrum assembly for a signal source or a spectrum analyzer, which can realize the spread of a fast-hopping signal from 0-400MHz to 0-14GHz, and comprises 4 parts, namely a DDS generating circuit, a frequency doubling circuit, a first mixing and switching filtering frequency selecting circuit/a first spread spectrum circuit, a second mixing and switching filtering frequency selecting circuit/a second spread spectrum circuit, a third mixing and switching filtering frequency selecting circuit/a third spread spectrum circuit.

As shown in fig. 2, the DDS generating circuit and the frequency doubling circuit include: a first frequency source (LO-1), a first DDS (T1), a first filter (low pass) 0-400 MHz (F1), a first and second single pole double throw switch (S1, S2), a second filter (bandpass) 200 MHz-400 MHz (F2), a third and fourth filter (bandpass) 400 MHz-800 MHz (F3, F4), a first and second amplifier (A1, A2), a first frequency multiplier (B1).

As shown in fig. 3, the first mixing and switching filter frequency selecting circuit includes: the second, third and fourth frequency sources (LO-2, LO-3, LO-4), fifth and sixth filters (low pass) 0 to 800MHz (F5), fourth, fifth and sixth switches (single pole single throw switches) (S4, S5, S6), third and tenth switches (single pole double throw switches) (S3, S10), seventh, eighth and ninth switches (single pole triple throw switches) (S7, S8, S9), sixth and eighth filters (band pass) 320MHz to 800MHz (F6), seventh and eighth filters (band pass) 1280MHz to 1760MHz (F7, F8), eleventh and twelfth filters (band pass) 1760MHz to 2240MHz (F11, F12), third, fourth, fifth and sixth amplifiers (band pass) 320MHz to 1280MHz (F7, F8), and first mixer (A4, A5, a 1).

As shown in fig. 4, the second mixing and switching filter frequency selecting circuit includes: a fifth frequency source, a sixth frequency source, a seventh frequency source, and an eighth frequency source (LO-5, LO-6, LO-7, LO-8), a thirteenth filter (low pass) 0 to 2240MHz (F13), a twelfth switch, a thirteenth switch, a fourteenth switch, a fifteenth switch (single pole single throw switch) (S12, S13, S14, S15), an eleventh switch, a nineteenth switch (single pole double throw switch) (S11, S19), a sixteenth switch, a seventeenth switch, and an eighteenth switch (single pole four throw switch) (S16, S17, S18), a thirty-fourth filter (bandpass) 800MHz to 1990MHz (F14), a fifteenth filter, a sixteenth filter (bandpass) 2240MHz to 3430MHz (F15, F16), a seventeenth filter, an eighteenth filter (bandpass) 3430MHz to 4620MHz (F17, F18), a nineteenth filter, a twentieth filter (4620 MHz to 5810MHz (F19), a twenty-fourth filter (bandpass 20 MHz), a twenty-fourth filter (bandpass) and a twenty-fourth filter (bandpass) 800MHz to 5810MHz (F20 MHz), a twenty-fourth filter (bandpass) and a nineteenth amplifier (bandpass) 2240MHz to 7000 (7 a, A7, a-eighth amplifier (bandpass) 10MHz to eighteenth amplifier (bandpass) 10 MHz).

As shown in fig. 5, the third mixing and switching filter frequency selecting circuit includes: ninth, tenth and eleventh frequency sources (LO-9, LO-10, LO-11), twenty-third filters (low pass) 0 to 7000MHz (F23), twenty-first, twenty-second, twenty-third (single pole single throw) switches (S21, S22, S23), twenty-first, twenty-seventh (single pole double throw) switches (S20, S27), twenty-fourth, twenty-fifth and twenty-sixth (single pole triple throw) switches (S24, S25, S26), twenty-fifth filters (bandpass) 2255MHz to 4605MHz (F24), twenty-fifth filters, twenty-sixth filters (bandpass) 7000 to 9350MHz (F25, F26), twenty-seventh filters, twenty-eighth filters (bandpass) 9350MHz to 11700MHz (F27, F28), twenty-ninth filters, thirty-fourth filters (bandpass) 1170 MHz to 14000MHz (F29, F30), thirteenth amplifiers (bandpass) and thirteenth amplifiers (bandpass) 7000MHz to 9300 MHz (F25, F30), thirteenth amplifiers (bandpass) 7000MHz to 9350MHz (F25, F26), and thirty-fourth filters (bandpass) and thirty-fifth amplifiers (31 a) and thirty-fifth amplifiers (31, 31 a to thirty-third amplifiers (15 MHz) and (lowpass) 3 MHz and (lowpass) filters).

The local oscillation frequency point and the relation between each frequency segment and the final output frequency set by the detailed mixer are shown in table 1.

List of frequency correspondence list

The working principle is as follows:

(1) The DDS circuit generates an intermediate frequency signal of 0-400MHz, the bandwidth of the DDS circuit is firstly expanded to 800MHz, and a single-pole double-throw switch is used for switching and selecting 0-400MHz and 400MHz-800MHz.

(2) The first mixer input is divided into two sections: 320MHz-400MHz and 400MHz-800MHz.

The first mixer local oscillator is 1600MHz and the output is 800MHz-1280MHz.

The first mixer local oscillator is 2080MHz, and the output is divided into 1280MHz-1680MHz,1680MHz-1760MHz.

The first mixer local oscillator is 2560MHz, and the output is divided into 1760MHz-2160MHz and 2160MHz-2240MHz.

(3) The second mixer input 800MHz-1990MHz is divided into five segments: 800MHz-1200MHz,1200MHz-1280MHz,1280MHz-1680MHz,1680MHz-1760MHz,1760MHz-1990MHz.

The second mixer local oscillation is 4230MHz, and the output is 2240MHz-3430MHz.

The second mixer local oscillator is 5420MHz, and the output is 3430MHz-4620MHz.

The second mixer local oscillator is 6610MHz and the output is 4620MHz-5810MHz.

The second mixer local oscillator is 7800MHz and the output is 5810MHz-7000MHz.

(4) Third mixer input 2240MHz-5795MHz.

The local oscillation of the third mixer is 12795MHz, the corresponding input is 3445MHz-5795MHz, and the output is

7000MHz-9350MHz。

The local oscillation of the third mixer is 13955MHz, the corresponding input is 2255MHz-4605MHz, and the output is

9350MHz-11700MHz。

The local oscillation of the third mixer is 16305MHz, the corresponding input is 2240MHz-4605MHz, and the output is

11700MHz-14065MHz。

The relationship between the output frequency and the input frequency is shown in table 1. The input to the output is mainly divided into the following cases:

① Direct output, without going through a mixer, e.g. 0-400MHz.

② The output is passed through a frequency doubler without passing through a mixer, such as 400MHz-800MHz.

③ Only through the first mixer, e.g. 800MHz-1200MHz.

④ Only the first mixer and the second mixer, e.g., 2240MHz-2470MHz.

⑤ Only the first mixer and the third mixer, e.g. 7000MHz-7385MHz, are passed.

⑥ Through a first mixer, a second mixer, and a third mixer, such as 14065MHz-14145MHz.

The output frequencies of the sections are arranged in order from small to large. Because the 3 mixers all adopt a high local oscillation scheme, the output intermediate frequency and the input radio frequency are in inverse spectrum relation. In the superheterodyne scheme, the most critical is that the mixer outputs intermediate frequency selection, and the spurious distribution is determined by the intermediate frequency selection, so that the design difficulty of the system filter is determined. There are mainly four principles: (1) avoiding half intermediate frequency; (2) mixing spurious emissions are reduced to fall into the intermediate frequency as little as possible; (3) harmonics of the intermediate frequency are to be able to be pushed out of band; (4) enough transition band to reject the image.

In the three-time mixing, the output intermediate frequency is larger than the input radio frequency and is up-converted. If the spurious frequency conversion using the high local oscillator scheme is smaller than the spurious frequency conversion using the low local oscillator scheme. The mixer local oscillator selects a high local oscillator scheme. By selecting a region with smaller relative spurious, and combining the design and selection of the filter, spurious output can be effectively reduced, so that spurious suppression capability of output intermediate frequency signals can be improved.

Specific frequencies refer to table 1, control voltages corresponding to the switches are needed to be provided for switching on and off of the switches, and then local oscillation frequency points refer to settings in the table.

1. Radio frequency path process analysis

(1): After the radio frequency input signal of 0-400MHz passes through the frequency multiplier, the original frequency band is divided into two paths by a single-pole double-throw switch, one path of the radio frequency input signal of 0-400MHz and the other path of the radio frequency input signal of 400MHz-800MHz. And then one path of the signal is selected to be output to the lower section radio frequency link through the single-pole double-throw switch.

(2): The single pole double throw switch is connected with the previous stage. The last section is divided into two paths by a single-pole double-throw switch, one path is 0-800MHz, the other path is 800MHz-1280MHz,1280MHz-1760MHz and 1760MHz generated after the first mixing, and one section is selected to be output. And then one path is selected from the two paths through a single-pole double-throw switch to be output to a lower section radio frequency link.

(3): The single pole double throw switch is connected with the previous stage. The last section is divided into two paths by a single-pole double-throw switch, one path is 0-2240MHz, the other path is 2240MHz-3430MHz,3430MHz-4620MHz,4620MHz-5810MHz,5810MHz-7000MHz generated after the second mixing, and one section is selected to be output. And then one path is selected from the two paths through a single-pole double-throw switch to be output to a lower section radio frequency link.

(4): The single pole double throw switch is connected with the previous stage. The last section is divided into two paths by a single-pole double-throw switch, one path is 0-7000MHz, the other path is 7000MHz-9350MHz,9350MHz-11700MHz and 11700MHz generated after third mixing, and one section of output is selected. And then one path of the two paths is selected to be output through a single-pole double-throw switch.

The DDS signal is realized from 0-400MHz to 0-14GHz broadband spread spectrum component, a control circuit is arranged in the DDS signal, and a program control command of an external computer is received to perform switching so as to complete local oscillator frequency point selection and turn-off control. Under the control of an external computer, the fast scan test of the broadband signal is completed together with the signal/spectrum analyzer.

2. Radio frequency output signal analysis

The spurious and phase noise of the wideband rf signal spreading device of this example is analyzed in detail below in conjunction with fig. 6-11.

(1) Stray analysis;

(1.1): DDS generating circuit and frequency doubling circuit

The DDS is AD9912, the clock can adopt 1GHz, the output frequency of the DDS is 0-400MHz, and the maximum output frequency is 40% of the frequency of the DDS clock. The DDS itself is stray 70dBc.

The 2-frequency multiplier circuit generates harmonics. The 1/2*F and 3/2*F subharmonic spurs are worst 20dBc. The band pass filter section filtering can suppress subharmonic spurious to 60dBc.

(1.2): First frequency mixing and switching filtering frequency selecting circuit

The first mixing, the local oscillator selects one from three point frequencies of 1600MHz/2080MHz/2560MHz as the mixing local oscillator. When one frequency point is opened, the other two frequency points are cut off. The switch isolation is guaranteed by (S4, S5, S6) SPST and (S7) SP3T two-stage switches. The isolation can reach 70dBc. I.e. the spurious suppression is to 70dBc.

The mixing is carried out by adopting a high local oscillation mode, and in the intermodulation spurs of three-section mixing, (800 MHz-1280 MHz) and (1280 MHz-1760 MHz), the maximum intermodulation spurs are 2 times of RF, and the spurs are suppressed by 58.6dBc. The maximum spurious (1760 MHz-2240 MHz) is-2 RF+LO, and spurious suppression is 76dBc.

(1.3): Second frequency mixing and switching filtering frequency selecting circuit

And a second mixing, wherein the local oscillator is selected from four point frequencies of 4230MHz/5420MHz/6610MHz/7800MHz to be used as a mixing local oscillator. When one frequency point is opened, the other three frequency points are cut off. The switch isolation is guaranteed by (S12, S13, S14, S15) SPST and (S16) SP4T two-stage switches. The isolation can reach 70dBc. I.e. the spurious suppression is to 70dBc.

The mixing is carried out by adopting a high local oscillation mode, and in the intermodulation spurs of four sections of mixing, (2240 MHz-3430 MHz) and (3430 MHz-4620 MHz), the maximum intermodulation spurs are 2 RF, and the spurs are suppressed by 58.6dBc. (4620 MHz-5810 MHz) and (5810 MHz-7000 MHz) have a maximum spurious of-2 RF+LO, with spurious suppression of 76dBc.

(1.4): Third frequency mixing and switching filtering frequency selecting circuit

And thirdly, selecting one local oscillator from three point frequencies of 12795MHz/13955MHz/16305MHz as a mixing local oscillator. When one frequency point is opened, the other two frequency points are cut off. The switch isolation is guaranteed by (S21, S22, S23) SPST and (S24) SP3T two-stage switches. The isolation can reach 70dBc. I.e. the spurious suppression is to 70dBc.

The mixing is carried out by adopting a high local oscillation mode, and in the intermodulation spurs of three-section mixing, the maximum intermodulation spurs (7000 MHz-9350 MHz) are 2 RF, and the spurs are suppressed to 58dBc. The maximum intermodulation spurious (9350 MHz-11700 MHz) is-2 x RF+LO, and the spurious suppression is 76dBc. The maximum spurious (11700 MHz-14000 MHz) is 3 rf and the spurious suppression is 98dBc.

(2) And (3) phase noise analysis:

The phase noise of the output signal depends on the 3 mixed dot frequency local oscillator signals and the DDS signal.

(2.1): DDS generating circuit and frequency doubling circuit

The phase noise of the DDS signal is determined by the phase noise of the input clock LO-1 and the DDS device's own noise. The frequency doubling circuit may deteriorate the phase noise by 20lg2, i.e. 6dB.

(2.2): First frequency mixing and switching filtering frequency selecting circuit

The first mixing produces frequencies 800MHz-2240MHz, and the phase noise is determined by the phase noise of local oscillator point frequencies (160 MHz,2080MHz,2560 MHz) and 320MHz-800MHz output from (2.1).

(2.3): Second frequency mixing and switching filtering frequency selecting circuit

The second mixing produces frequencies 2240MHz to 7000MHz, and the phase noise is determined by the phase noise of local oscillation point frequencies (4230 MHz,5420MHz,6610MHz,7800 MHz) and 800MHz to 1990MHz output in (2.2).

(2.4): Third frequency mixing and switching filtering frequency selecting circuit

The third mixing produces frequencies 0-14065MHz, and the phase noise is determined by the phase noise of local oscillator point frequencies (12795 MHz,13955MHz,16305 MHz) and 2240MHz-5795MHz output from (2.3).

The utility model needs to generate 11 point frequency sources, wherein 1 point frequency source is used as a DDS clock, and the other 10 point frequency sources are switchable point frequency local oscillators in the three-time mixing process. These 11 point sources are all generated directly using PLL devices of an integrated VCO. The power-on state is always kept in an on state, and the frequency hopping time index is met by switching on and off of a switch. The integrated phase-locked loop chip is convenient to use, and the final point frequency is high in frequency and can be obtained by adopting a frequency multiplication method.

In the embodiment, the frequency spreading component is controlled by an external computer, and the rapid sweep test of the 0-14GHz broadband signal is completed according to the information such as the switch configuration of the 0-400MHz DDS generator and the frequency spreading component and matching with frequency spreading software.

The foregoing has shown and described the basic principles, principal features and advantages of the utility model. It will be appreciated by persons skilled in the art that the above embodiments are not intended to limit the utility model in any way, and that all technical solutions obtained by means of equivalent substitutions or equivalent transformations fall within the scope of the utility model.

Claims (8)

1. A wideband DDS spreading device, comprising:

the DDS generation circuit comprises a first frequency source (LO-1) and a first DDS (T1) for generating an intermediate frequency signal;

The frequency doubling circuit comprises a first low-pass filtering branch and a frequency doubling branch, and is used for dividing the intermediate frequency signal into two paths and respectively inputting the two paths into the first low-pass filtering branch and the frequency doubling branch; the frequency doubling branch performs frequency doubling treatment on the received signals to obtain corresponding frequency band signals; the output ends of the first low-pass filtering branch and the frequency doubling branch are provided with a single-pole double-throw switch which is commonly connected and used for selecting one of the single-pole double-throw switches as the output of the frequency doubling circuit;

The multi-stage spread spectrum circuit is provided with a radio frequency signal input end, a second low-pass filtering branch, a local oscillator circuit, a spread spectrum branch and a spread spectrum signal output end, wherein the radio frequency signal input end of the first-stage spread spectrum circuit receives the frequency band signals output by the frequency doubling circuit, and the radio frequency signal input ends of the other spread spectrum circuits receive the frequency band signals output by the last-stage spread spectrum circuit; the frequency band signal received by the radio frequency signal input end is divided into two paths, the two paths are respectively connected into a second low-pass filter circuit and a spread spectrum branch, the local oscillator circuit is used for providing local oscillator signals for the spread spectrum branch, a mixer (M1; M2; M3) used for carrying out mixing processing on the frequency band signal received by the spread spectrum branch and the local oscillator signals is arranged in the spread spectrum branch, and the output ends of the second low-pass filter circuit and the spread spectrum branch are provided with a single-pole double-throw switch which is commonly connected and used for selecting one of the two paths as the output of the spread spectrum circuit.

2. The wideband DDS spreading apparatus of claim 1 wherein: the frequency doubling circuit further comprises a first switch (S1), a second filter (F2) and a second switch (S2), wherein the first switch (S1) and the second switch (S2) are single-pole double-throw switches, and the second filter (F2) is a band-pass filter;

The DDS generation circuit generates a 0-Fa frequency band signal, a first switch (S1) and a second filter (F2) are used for dividing the 0-Fa frequency band signal into two paths, one path is the 0-Fa frequency band signal, the 0-Fa frequency band signal is input into a first low-pass filtering branch, and the 0-Fa frequency band signal is obtained after low-pass filtering; the other path is Fa/2-Fa frequency band signals, and the Fa/2-Fa frequency band signals are obtained after frequency doubling treatment by inputting a frequency doubling branch; and the second switch (S2) is used for selecting one path from the 0-Fa frequency band signal and the Fa-2Fa frequency band signal to be used as the output of the frequency doubling circuit.

3. The wideband DDS spreading apparatus of claim 1 wherein: in the frequency doubling circuit, the frequency doubling branch comprises a first amplifier (A1), a frequency doubling device (B1), a third filter (F3), a second amplifier (A2) and a fourth filter (F4) which are connected in series, wherein the third filter (F3) and the fourth filter (F4) are bandpass filters with different passbands.

4. The wideband DDS spreading apparatus of claim 1 wherein: each stage of spread spectrum circuit is provided with a first single-pole double-throw switch (S3; S11; S20), a second single-pole double-throw switch (S10; S19; S27), a first single-pole multi-throw switch (S7; S16; S24), a second single-pole multi-throw switch (S8; S17; S25) and a third single-pole multi-throw switch (S9; S18; S26), and a front band-pass filter (F6; F14; F24);

The radio frequency signal input end divides a received frequency band signal into two paths through a first single-pole double-throw switch (S3; S11; S20) and a front band-pass filter (F6; F14; F24), one path is a 0-Fbi frequency band signal, the second low-pass filter circuit is connected to the radio frequency signal input end, the 0-Fbi frequency band signal is obtained after low-pass filtering processing, the other path is a Fbj-Fbi frequency band signal, the signal is input into a spread spectrum branch, b represents a b-stage spread spectrum circuit, 0< Fbj < Fbi, and Fbi represents the maximum frequency of the frequency band signal input by the b-stage spread spectrum circuit;

The local oscillation circuit is internally provided with a plurality of frequency sources (LO-2-LO-4; LO-5-LO-8; LO-9-LO-11) and selects one path of output as local oscillation signals through a first single-pole multi-throw switch (S7; S16; S24);

The spread spectrum branch circuit also comprises a plurality of band-pass filter circuits, a mixer (M1; M2; M3) is used for carrying out mixing processing on the Fbj-Fbi frequency band signals and local oscillator signals to obtain Fbi-Fbk frequency band signals, the output end of the mixer (M1; M2; M3) inputs signals of different frequency bands to each band-pass filter circuit through a second single-pole multi-throw switch (S8; S17; S25), each band-pass filter circuit has different pass bands and jointly forms the allowed frequency range as Fbi-Fbk, fbk represents the maximum frequency of spread spectrum signals output by a b-th level spread spectrum circuit, and the output end of each band-pass filter circuit is jointly connected with a third single-pole multi-throw switch (S9; S18; S26);

The second single-pole double-throw switch (S10; S19; S27) is connected with the output end of the third single-pole double-throw switch (S9; S18; S26) and is used for selecting one path from the 0-Fbi frequency band signal and the Fbi-Fbk frequency band signal to be used as the output of the spread spectrum circuit.

5. The wideband DDS spreading apparatus of claim 4 wherein: in the spread spectrum branch, each band-pass filter circuit comprises an amplifier (A4-A6; A8-A11; A13-A15), and the input end and the output end of the amplifier are respectively provided with a band-pass filter (F7-F8; F9-F10; F11-F12; F15-F16; F17-F18; F19-F20; F21-F22; F25-F26; F27-F28; F29-F30) with the same passband.

6. The wideband DDS spreading apparatus of claim 4 wherein: in the local oscillation circuit, frequency sources are directly generated by using PLL devices of an integrated VCO, the output ends of the frequency sources (LO-2-LO-4; LO-5-LO-8; LO-9-LO-11) are connected to the input end of the first single-pole multi-throw switch (S7; S16; S24) through a single-pole single-throw switch (S4-S6; S12-S15; S21-S23), and an amplifier (A3; A7; A12) is arranged between the output end of the first single-pole multi-throw switch (S7; S16; S24) and a corresponding mixer.

7. The wideband DDS spreading apparatus of claim 1 wherein: the first low-pass filtering branch and the second low-pass filtering branch are realized by adopting low-pass filters, and all switches are switched on and off by corresponding control voltages.

8. The wideband DDS spreading apparatus of claim 1 wherein: the device comprises three-stage spread spectrum circuits, namely a first-stage spread spectrum circuit, a second-stage spread spectrum circuit and a third-stage spread spectrum circuit, wherein,

The DDS generation circuit generates a signal with the frequency range of 0-400 MHz;

In the frequency doubling circuit, the 0-400MHz frequency band signal is divided into two paths, one path is the 0-400MHz frequency band signal, the other path is the 200-400MHz frequency band signal, the 400-800MHz frequency band signal is obtained through the frequency doubling branch, and the frequency doubling circuit outputs the 0-800MHz frequency band signal;

In the first-stage spread spectrum circuit, a frequency band signal received by a radio frequency signal input end is divided into two paths, one path is a frequency band signal of 0-800MHz, and the other path is a frequency band signal of 320-800 MHz; the local oscillation signal comprises three frequency sources with the frequencies of 1600MHz, 2080MHz and 2560MHz respectively; the spread spectrum branch comprises three band-pass filters, the pass bands of which are respectively 800-1280MHz, 1280-1760MHz and 1760-2240 MHz; the first spread spectrum circuit outputs a signal of 0-2240MHz frequency band;

In the second-stage spread spectrum circuit, the frequency band signal received by the radio frequency signal input end is divided into two paths, one path is a 0-2240MHz frequency band signal, and the other path is a 800-1990MHz frequency band signal; the local oscillation signal comprises four frequency sources with frequencies of 4230MHz, 5420MHz, 6610MHz and 7800MHz respectively; the spread spectrum branch comprises four band-pass filters, the pass bands of which are 2240-3430MHz, 3430-4620MHz, 4620-5810MHz and 5810-7000MHz respectively; the second spread spectrum circuit outputs a signal of 0-7000MHz frequency band;

In the third-stage spread spectrum circuit, a frequency band signal received by a radio frequency signal input end is divided into two paths, one path is a 0-7000MHz frequency band signal, and the other path is a 2240-5795MHz frequency band signal; the local oscillation signal comprises three frequency sources with frequencies of 12795MHz, 13955MHz and 16305MHz respectively; the spread spectrum branch circuit comprises three band-pass filters, the pass bands of the three band-pass filters are 7000-9350MHz, 9350-11700MHz and 11700-14000MHz respectively, and the third spread spectrum circuit outputs signals in the frequency band of 0-14000 MHz.