CN112688686A - Miniaturized broadband frequency synthesizer - Google Patents
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- CN112688686A CN112688686A CN202011469298.2A CN202011469298A CN112688686A CN 112688686 A CN112688686 A CN 112688686A CN 202011469298 A CN202011469298 A CN 202011469298A CN 112688686 A CN112688686 A CN 112688686A
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Abstract
The invention relates to a miniaturized broadband frequency synthesis device, which adopts a scheme of combining a multi-ring phase-locking technology and a direct digital frequency synthesis technology and mainly comprises a second local oscillator phase-locked loop PLL1, a DDS circuit, a first local oscillator loop and a low-noise step phase-locked loop; the first local oscillator adopts a multi-loop lock frequency synthesis scheme, wherein a main loop feedback channel adopts a scheme combining frequency division and frequency mixing, and the loop is in a locked state under any sweep width without a complex frequency preset circuit and algorithm; when the frequency is switched, the current integrated voltage is kept by disconnecting the analog switch in the loop filter, so that the VCO frequency is kept stable at the moment of switching, and the problem of lock losing is avoided. By adopting the high-integration low-noise stepping phase-locked loop, the problems of complex circuit and high stray of output signal sideband of a sampling scheme are avoided. The hand-held frequency spectrograph for the multi-scene test is miniaturized, light in weight, low in power consumption and long in endurance design.
Description
Technical Field
The invention relates to the field of frequency synthesis, in particular to a miniaturized broadband frequency synthesis device.
Background
With the rapid development of wireless communication technology and military electronic equipment, the use scenes of the handheld spectrum analyzer are more and more extensive, and besides the requirements of miniaturization, low power consumption and multiple measurement functions, the product per se also has performance indexes close to that of a middle-grade desk type spectrum analyzer, so that higher requirements are provided for the circuit design including the synthesis of the first local oscillation frequency of the broadband of the handheld spectrum analyzer.
The first local oscillator of the hand-held spectrum analyzer has two schemes commonly used at present, the first one is a single-ring frequency synthesis scheme, the first one comprises a frequency synthesis chip, a broadband VCO, an active loop filter, a fractional frequency divider, a directional coupler and the like, and a phase-locked loop circuit is formed by the circuits. The second is a multi-loop frequency synthesis scheme, which includes a plurality of phase-locked loops, such as a fractional loop, a sampling local oscillator loop, and a first local oscillator VCO main loop, and the functional block diagram is shown in fig. 1. In the multi-ring phase-locked frequency synthesis scheme, a decimal ring provides a phase-locked reference signal of 50-100 MHz for a first local oscillator VCO main ring, and due to the adoption of a 32 or 48-digit decimal frequency division design, the high-frequency resolution index of the whole machine is ensured and a frequency sweeping function is provided; the sampling local oscillator ring adopts a design scheme of interpolating a frequency mixer through a feedback channel, the feedback frequency dividing ratio of the phase-locked loop is reduced, so that a local oscillator signal with high spectral purity is output to a sampler, sampling frequency conversion is carried out on a broadband VCO output signal (directly output or output through frequency division) to generate a frequency signal which is the same as a decimal ring, loop filtering is carried out after phase discrimination and a charge pump, and the generated error voltage controls the VCO output frequency. The multi-ring frequency synthesis circuit has the advantages of excellent phase noise index, small sideband spurious and the like, and plays a very key role in realizing low phase noise and low spurious index for the whole handheld spectrum analyzer.
In the first local oscillator frequency synthesis scheme of the traditional hand-held frequency spectrograph, the frequency of a sampling local oscillator is usually 600-800 MHz, the output frequency of a VCO is 4-8 GHz or 6-12 GHz, a broadband local oscillator feedback channel performs sampling frequency conversion by utilizing multiple harmonics of the sampling local oscillator and radio frequency signals, the problem that the frequency is locked to unnecessary harmonic times or current sampling harmonic mirror frequency easily occurs, a special DAC control circuit is required to be added at a tuning end of the VCO to avoid the problem of the error locking, tuning voltage is required to be set in advance in an open-loop state before a certain frequency is set, so that the broadband VCO is kept near a locking frequency, then a phase-locked loop circuit is closed, final locking is realized by the capturing and tracking capacity of a loop, a complex calibration algorithm and a complex phase-locked loop test process are required to perform background touch and data fitting on the tuning characteristic of the VCO, the debugging process is long and is greatly influenced by the, frequency drift is liable to occur with changes in time and temperature characteristics causing an out-of-lock problem. In addition, the sampling vibration implementation scheme in the traditional scheme is complex, 100MHz frequency reference needs to be converted into 600MHz in a frequency doubling mode for realizing low phase noise, 100MHz, 300MHz and 600MHz in the frequency doubling conversion process and the power of a sampling local oscillator are high, the handheld frequency spectrum analyzer is limited by the size of the whole machine, all local oscillator frequency synthesis circuits are implemented on the same circuit board, high-power signals easily cause interference to high-sensitivity circuits including a frequency synthesis chip, a sampler and a mixer, so that sideband spurs are generated, although partial spurs can be avoided in a mode of changing the local oscillator and intermediate frequency combination of the sampler, the influence on the quality of a final local oscillator broadband output signal can not be eliminated by partial frequency point spurs.
At present, circuits such as a sampling local oscillator and a fractional ring in a handheld spectrum analyzer are mainly constructed by combining circuits such as a frequency synthesizer, a VCO (voltage controlled oscillator), an active loop filter, a mixer and a filter, the circuits occupy a large area and have high power consumption, and the characteristics of the whole handheld spectrum analyzer such as volume and power consumption are influenced.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a miniaturized broadband frequency synthesis device, which adopts a scheme of combining a multi-ring phase locking technology and a direct digital frequency synthesis technology, has reasonable design, overcomes the defects of the prior art and has good effect.
In order to achieve the purpose, the invention adopts the following technical scheme:
a miniaturized broadband frequency synthesis device comprises a second local oscillator phase-locked loop PLL1, a DDS circuit, a first local oscillator loop and a low-noise step phase-locked loop; the input end of a second local oscillator phase-locked loop PLL1 is connected with the input end of a low-noise step phase-locked loop, a second local oscillator phase-locked loop PLL1, a DDS circuit and a first local oscillator loop are sequentially connected, the second local oscillator phase-locked loop PLL1 and the first local oscillator loop are connected to a mixer in a radio frequency channel of a frequency spectrograph, and a 3 frequency multiplier and the low-noise step phase-locked loop are connected to the first local oscillator loop;
the first local oscillation loop comprises a first local oscillation frequency synthesizer, a single-pole single-throw analog switch, a loop filter, a broadband VCO (voltage controlled oscillator), a directional coupler, a frequency divider 2, a first single-pole double-throw radio frequency switch, a feedback N frequency divider, a feedback amplifier, a frequency mixer, a filter and a second single-pole double-throw radio frequency switch; the first local oscillator frequency synthesizer is sequentially connected with a single-pole single-throw analog switch, a loop filter, a broadband VCO (voltage controlled oscillator) and a directional coupler, the directional coupler is respectively connected with a frequency mixer and a frequency divider 2 in a radio frequency channel of the frequency spectrograph, the frequency divider 2 is connected with a first single-pole double-throw radio frequency switch, the first single-pole double-throw radio frequency switch is divided into two paths, one path is connected with a feedback N frequency divider, the other path is connected with a feedback amplifier, the frequency mixer and the filter, the two paths are commonly connected to a second single-pole double-throw radio frequency switch, and the second single-pole double-throw radio frequency switch is connected to the first local oscillator frequency synthesizer.
Preferably, the first local oscillator frequency synthesizer and the integrated phase-locked chip comprise a reference R frequency divider, a feedback N frequency divider, a phase frequency detector and a charge pump, wherein a reference signal enters the phase frequency detector through the reference R frequency divider, a feedback signal enters the phase frequency detector through the feedback N frequency divider, and the phase frequency detector outputs an error current to enter the loop filter through the charge pump according to a phase error of two paths of signals.
Preferably, the single-pole single-throw analog switch has low on-resistance, high isolation index and nA-level leakage current, is used for a tuning voltage holding function when the main loop is switched from the frequency division mode to the frequency mixing mode, and ensures that the VCO frequency is kept stable at the switching moment of the radio frequency switch due to the fact that the phase-locked loop charge pump is in a high-resistance state when the phase-locked loop is switched off.
Preferably, the loop filter is an active loop filter formed by an operational amplifier, an analog switch and a resistor capacitor, and is used for loop parameter control and noise suppression of the wideband VCO, wherein the resistor and the capacitor are connected in series, and the operational amplifier is connected in parallel with the resistor and the capacitor.
Preferably, a 100MHz signal generated by the reference ring crystal oscillator is multiplied by a frequency multiplier 3 to 300MHz and then is used as a reference signal of the low noise step phase-locked loop, and the reference signal is further divided into 150MHz or 60MHz in a reference R frequency divider inside the low noise step phase-locked loop; the low-noise stepping phase-locked loop adopts a low-noise frequency synthesis chip with a built-in VCO (voltage controlled oscillator), has very good background noise and VCO noise, the phase discrimination frequency of the stepping phase-locked loop is selected to be more than 60MHz, the output frequency of 3-6 GHz is used as a radio frequency signal of a local oscillator feedback channel frequency mixer (the frequency difference with a frequency division 2 signal output by the first local oscillator VCO is 50-100 MHz), and the low-noise stepping phase-locked loop can generate signals with low noise and large stepping frequency by using a high phase discrimination frequency and a low feedback frequency division ratio.
Preferably, the second local oscillator phase-locked loop PLL1 generates a second local oscillator signal required by the complete machine, and provides 1600MHz frequency reference with low phase noise for the DDS circuit; the DDS circuit generates a sweep frequency signal in a frequency range of 50-100 MHz in a direct digital frequency synthesis mode to provide a low-phase noise phase-locked reference signal for the first local oscillator frequency synthesizer, and has the advantages of low phase noise and spurious emission and extremely high scanning speed compared with a fractional ring; the first local oscillator frequency synthesizer compares the phase difference of the reference signal and the feedback signal, and outputs error current to the loop filter through the internal charge pump to convert the error current into error voltage to tune the output frequency of the VCO; the loop filter comprises two different loop parameters under a frequency mixing mode and a frequency dividing mode, and the complete machine performs selection control on the loop filter according to the sweep width setting; the broadband VCO selects a frequency band of 6-12 GHz, and other frequency bands such as 4-8 GHz VCO can be selected according to different application occasions; the directional coupler outputs the VCO signal main circuit to a mixer in a radio frequency channel of the frequency spectrograph, and outputs the auxiliary circuit to a feedback channel of the phase-locked loop;
preferably, in the feedback channel, a 2-frequency divider converts a local oscillation feedback signal of 6-12 GHz into 3-6 GHz, the design difficulty of the back-end circuit is reduced by reducing the frequency, if the frequency band of the VCO is consistent with the working frequency interval of the back-end mixer and the stepping ring, the frequency divider is not needed, and the first single-pole double-throw radio frequency switch selects a frequency dividing channel or a frequency mixing channel according to the host width scanning setting; the frequency division path is that 3-6 GHz feedback signals output by the 2-frequency divider generate feedback phase discrimination signals within a range of 50-100 MHz after being subjected to N frequency division by the feedback N-frequency divider, and the feedback phase discrimination signals are fed back to the first local oscillator frequency synthesizer; and the frequency mixing channel is that a 3-6 GHz feedback signal output by the 2 frequency divider is amplified by the feedback amplifier and then used as a local oscillation signal of the frequency mixer, the frequency mixer mixes the 3-6 GHz local oscillation signal of the feedback channel with a radio frequency signal generated by the low-noise stepping phase-locked loop, and an intermediate frequency signal of 50-100 MHz is output and fed back to the first local oscillation frequency synthesizer.
Preferably, the feedback channel of the first local oscillator main loop adopts a combination of an N frequency division mode and a frequency mixing mode, the N frequency division mode is adopted when the whole machine is set to be wide-scan, the high scanning speed is exchanged by the sacrifice of phase noise, the frequency mixing mode is adopted when the whole machine is set to be small-scan, the low-noise step phase-locked loop provides a radio-frequency signal with high spectral purity to the frequency mixer, and the excellent spectral purity index is obtained by reducing the feedback frequency division ratio.
Preferably, the frequency sweeping function and the small frequency stepping of the frequency mixing mode are realized by a DDS circuit, and the realization of the large frequency stepping and the low phase noise index depends on the phase discrimination frequency and the phase noise index of a low noise stepping phase-locked loop; the scanning starting frequency presetting of the frequency mixing mode is realized in an N frequency division mode, after the frequency division mode sets a first local oscillator starting frequency, a single-pole single-throw analog switch at the rear end of a first local oscillator frequency synthesizer is switched off to maintain the current tuning voltage unchanged, and the single-pole single-throw analog switch is switched on after the frequency setting of the DDS and the stepping ring is completed, so that the first local oscillator output frequency can be quickly switched to the set frequency when a first single-pole double-throw radio frequency switch in a channel is switched.
Preferably, the division ratio N of the feedback N-divider is 64.
Preferably, the mixer is a nonlinear device, the intermediate frequency output port includes sum frequency, difference frequency, local oscillator signal, radio frequency signal of the radio frequency and the local oscillator, and multiple intermodulation product of the sum frequency, the difference frequency, the local oscillator signal and the radio frequency signal, and the filter is used for suppressing other frequencies except the difference frequency signal, so that the feedback phase discrimination signal of the first local oscillator has higher spectral purity.
The invention has the following beneficial technical effects:
the invention adopts the scheme of combining interpolation mixing and frequency division, does not need frequency presetting during multi-loop phase locking, and can ensure that a loop is in a phase locking state in any state; the DDS chip and the stepping phase-locked loop chip with high integration level are adopted, the main loop feedback channel adopts a mixing scheme, the circuit area is small, the control scheme is simple, the advantages of high scanning speed, high frequency spectrum purity, low power consumption, small size and the like are achieved, and a hardware basis is provided for miniaturization, light weight, low power consumption and long endurance design of the hand-held frequency spectrograph for the multi-scene test.
Drawings
FIG. 1 is a schematic diagram of a conventional multi-loop frequency synthesis scheme;
FIG. 2 is a schematic diagram of a miniaturized wideband frequency synthesizer according to the present invention;
FIG. 3 is a schematic diagram of a miniaturized wideband frequency synthesizer of the present invention;
1-a second local oscillator phase-locked loop PLL 1; 2-DDS circuit; 3-a first local oscillator frequency synthesizer; 4-single pole single throw analog switch; 5-a loop filter; 6-wideband VCO; 7-a directional coupler; an 8-2 frequency divider; 9-a first single pole double throw radio frequency switch; 10-feedback N-divider; 11-a feedback amplifier; 12-a mixer; 13-a filter; 14-a second single pole double throw radio frequency switch; 15-3 frequency doubler; 16-low noise step phase locked loop;
Detailed Description
The following description of the embodiments of the present invention will be made with reference to the accompanying drawings:
a miniaturized wideband frequency synthesizer, as shown in fig. 2 and 3, includes a second local oscillator phase-locked loop PLL1(1), a DDS circuit (2), a first local oscillator loop, and a low noise step phase-locked loop (16); the input end of a second local oscillator phase-locked loop PLL1(1) is connected with the input end of a low-noise step phase-locked loop (4), the second local oscillator phase-locked loop PLL1(1), a DDS circuit (2) and a first local oscillator loop are sequentially connected, the second local oscillator phase-locked loop PLL1 and the first local oscillator loop are connected to a mixer in a radio frequency channel of a frequency spectrograph, and a frequency multiplier (15) and a low-noise step phase-locked loop (16) are connected to the first local oscillator loop;
the first local oscillator loop comprises a first local oscillator frequency synthesizer (3), a single-pole single-throw analog switch (4), a loop filter (5), a broadband VCO (6), a directional coupler (7), a 2 frequency divider (8), a first single-pole double-throw radio frequency switch (9), a feedback N frequency divider (10), a feedback amplifier (11), a frequency mixer (12), a filter (13) and a second single-pole double-throw radio frequency switch (14); the first local oscillator frequency synthesizer (3) is sequentially connected with a single-pole single-throw analog switch (4), a loop filter (6), a broadband VCO (6) and a directional coupler (7), the directional coupler (7) is respectively connected with a frequency mixer and a frequency divider (8) in a radio frequency channel of a frequency spectrograph, the frequency divider (8) is connected with a first single-pole double-throw radio frequency switch (9), the first single-pole double-throw radio frequency switch (9) is divided into two paths, one path is connected with a feedback N frequency divider (10), the other path is connected with a feedback amplifier (11), a frequency mixer (12) and a filter (13), the two paths are commonly connected to a second single-pole double-throw radio frequency switch (14), and the second single-pole double-throw radio frequency switch (14) is connected to the first local oscillator frequency synthesizer (3).
Specifically, the first local oscillator frequency synthesizer (3) is an integrated phase-locked chip and comprises a reference R frequency divider, a feedback N frequency divider, a phase frequency detector and a charge pump, wherein a reference signal enters the phase frequency detector through the reference R frequency divider, a feedback signal enters the phase frequency detector through the feedback N frequency divider, and the phase detector outputs an error current to enter a loop filter through the charge pump according to phase errors of two paths of signals. .
Specifically, the single-pole single-throw analog switch (4) has low on-resistance, high isolation index and nA-level leakage current, and the VCO frequency is ensured to be stable at the switching moment of the radio frequency switch due to the fact that the phase-locked loop charge pump is in a high-resistance state when the phase-locked loop charge pump is switched off.
Specifically, the loop filter (5) adopts an active loop filter consisting of an operational amplifier, an analog switch and a resistor capacitor, wherein the resistor and the capacitor are connected in series, and the operational amplifier is connected with the resistor and the capacitor in parallel.
Specifically, the working process of the miniaturized broadband frequency synthesis device is as follows:
a 100MHz signal generated by a reference ring crystal oscillator is subjected to frequency multiplication by a frequency multiplier (14) to 300MHz and then is used as a reference signal of a low-noise stepping phase-locked loop (15), and the reference signal is further divided into 150MHz or 60MHz in a reference R frequency divider inside the low-noise stepping phase-locked loop (15); the low-noise step phase-locked loop (15) adopts a low-noise frequency synthesis chip with a built-in VCO, the phase discrimination frequency of the step phase-locked loop is selected to be more than 60MHz, and the output frequency is 3-6 GHz and is used as a radio frequency signal of a first local oscillation feedback channel frequency mixer (12).
A second local oscillator phase-locked loop PLL1(1) generates a second local oscillator signal required by the whole device and provides 1600MHz frequency reference with low phase noise for a DDS circuit (2); the DDS circuit (2) generates a sweep frequency signal in a frequency range of 50-100 MHz in a direct digital frequency synthesis mode to provide a low-phase noise phase-locked reference signal for the first local frequency synthesizer (3); the first local oscillator frequency synthesizer (3) compares the phase difference of the reference signal and the feedback signal, outputs error current to a loop filter (5) through an internal charge pump, and converts the error current into error voltage to tune the output frequency of the VCO; the loop filter (5) comprises two different loop parameters under the frequency mixing mode and the frequency dividing mode, and the whole machine carries out selection control on the loop filter (5) according to the setting of the sweep width; the method comprises the following steps that a broadband VCO (6) selects a frequency band of 6-12 GHz, a directional coupler (7) outputs a VCO signal main circuit to a mixer in a frequency spectrograph radio frequency channel, and an auxiliary circuit is output to a feedback channel of a phase-locked loop;
in a feedback channel, a 2-frequency divider (8) converts a first local oscillation feedback signal of 6-12 GHz into 3-6 GHz, and a first single-pole double-throw radio frequency switch (9) selects a frequency division channel or a frequency mixing channel according to the host width scanning setting; the frequency division path is that a 3-6 GHz feedback signal output by the frequency divider (8) is subjected to N frequency division by the feedback N frequency divider (10) to generate a feedback phase discrimination signal within a range of 50-100 MHz, and the feedback phase discrimination signal is fed back to the first local oscillator frequency synthesizer (3), wherein the frequency division ratio N is 64; the frequency mixing channel is that a 3-6 GHz feedback signal output by the 2 frequency divider (8) is amplified by the feedback amplifier (11) and then used as a local oscillation signal of the frequency mixer (12), the frequency mixer (12) mixes the 3-6 GHz local oscillation signal of the feedback channel with a radio frequency signal generated by the low-noise step phase-locked loop (15), and an intermediate frequency signal of 50-100 MHz is output and fed back to the first local oscillation frequency synthesizer (3).
Specifically, a feedback channel of the first local oscillator main loop adopts an N frequency division mode and a frequency mixing mode in combination, the N frequency division mode is adopted when the whole machine is set to be wide in scanning width, high scanning speed is exchanged by sacrificing phase noise, the frequency mixing mode is adopted when the whole machine is set to be small in scanning width, a low-noise stepping phase-locked loop provides a radio-frequency signal with high spectral purity to a frequency mixer, and the feedback frequency division ratio is reduced to obtain an excellent spectral purity index.
Specifically, the frequency sweeping function and the small frequency stepping of the frequency mixing mode are realized by a DDS circuit, and the realization of the large frequency stepping and the low phase noise index depends on the phase discrimination frequency and the phase noise index of a low noise stepping phase-locked loop; the scanning starting frequency presetting of the frequency mixing mode is realized in an N frequency division mode, after the frequency division mode sets a first local oscillator starting frequency, a single-pole single-throw analog switch at the rear end of a first local oscillator frequency synthesizer is switched off to maintain the current tuning voltage unchanged, and the single-pole single-throw analog switch is switched on after the frequency setting of the DDS and the stepping ring is completed, so that the first local oscillator output frequency can be quickly switched to the set frequency when a first single-pole double-throw radio frequency switch in a channel is switched.
Specifically, the mixer (12) is a nonlinear device, the intermediate frequency output port comprises sum frequency, difference frequency, local oscillator signal, radio frequency signal of radio frequency and local oscillator, and multiple intermodulation product of the sum frequency, the difference frequency, the local oscillator signal and the radio frequency signal, and the filter is used for inhibiting other frequencies except the difference frequency signal, so that the feedback phase discrimination signal of the first local oscillator has higher spectral purity.
The first local oscillation frequency synthesizer adopted by the invention presets tuning frequency by the feedback N frequency divider in a multi-ring phase-locked state, a low leakage current analog switch in a loop filter keeps tuning voltage, a radio frequency switch and the analog switch are switched after DDS frequency and step phase-locked loop frequency are set, so that the re-locking of multi-ring frequency is realized, and the frequency presetting of a VCO (voltage controlled oscillator) tuning end is not required to be additionally added with a preset DAC (digital-to-analog converter) circuit for multi-ring phase-locked; first local oscillator for feedback channel replaces the sampler under the multi-ring mode, has avoided in the sampling frequency conversion scheme except that the loss of the extra 5 ~ 8dB that causes of local oscillator doubling of frequency effect, under the condition that the circuit area reduces by a wide margin, replaces the phase noise index that the sample local oscillator can be better than the original scheme with step-by-step phase-locked loop to stray index also can promote by a wide margin.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.
Claims (10)
1. A miniaturized broadband frequency synthesis device is characterized by comprising a second local oscillator phase-locked loop PLL1, a DDS circuit, a first local oscillator loop and a low-noise step phase-locked loop; the input end of the second local oscillator phase-locked loop PLL1 is connected with the input end of the low-noise step phase-locked loop, the second local oscillator phase-locked loop PLL1, the DDS circuit and the first local oscillator loop are sequentially connected, the first local oscillator loop and the second local oscillator phase-locked loop PLL1 are connected to a mixer in a radio frequency channel of the frequency spectrograph, and the 3 frequency multiplier and the low-noise step phase-locked loop are connected to the first local oscillator loop;
the first local oscillation loop comprises a first local oscillation frequency synthesizer, a single-pole single-throw analog switch, a loop filter, a broadband VCO (voltage controlled oscillator), a directional coupler, a frequency divider 2, a first single-pole double-throw radio frequency switch, a feedback N frequency divider, a feedback amplifier, a frequency mixer, a filter and a second single-pole double-throw radio frequency switch; the first local frequency synthesizer is sequentially connected with a single-pole single-throw analog switch, a loop filter, a broadband VCO (voltage controlled oscillator) and a directional coupler, the directional coupler is respectively connected with a frequency mixer and a frequency divider 2 in a radio frequency channel of the frequency spectrograph, the frequency divider 2 is connected with a first single-pole double-throw radio frequency switch, the first single-pole double-throw radio frequency switch is divided into two paths, one path is connected with a feedback N frequency divider, the other path is connected with a feedback amplifier, the frequency mixer and a filter, the two paths are commonly connected to a second single-pole double-throw radio frequency switch, and the second single-pole double-throw radio frequency switch is connected to the first local frequency synthesizer.
2. The apparatus of claim 1, wherein the first local oscillator synthesizer is an integrated phase locked chip comprising a reference divider R, a feedback divider N, a phase frequency detector and a charge pump, wherein the reference signal enters the phase frequency detector through the reference divider R, the feedback signal enters the phase frequency detector through the feedback divider N, and the phase frequency detector outputs an error current to the loop filter according to the phase error of the two signals.
3. The apparatus of claim 1, wherein the single-pole single-throw analog switch has a low on-resistance, a high isolation index and a leakage current of nA level, and when the VCO is turned off, the VCO frequency is kept stable at the switching moment of the RF switch due to the high impedance state of the PLL charge pump during switching.
4. A miniaturized wideband frequency synthesizer according to claim 1, wherein said loop filter is an active loop filter formed by an operational amplifier, an analog switch and a resistor-capacitor, wherein the resistor and the capacitor are connected in series, and the operational amplifier is connected in parallel with the resistor and the capacitor.
5. The miniaturized wideband frequency synthesizer according to claim 1, wherein the 100MHz signal generated by the reference ring crystal oscillator is multiplied by 3 frequency multipliers to 300MHz and then used as the reference signal of the low noise step-locked loop, and the reference signal is further divided into 150MHz or 60MHz in the reference R frequency divider inside the low noise step-locked loop; the low-noise step phase-locked loop adopts a low-noise frequency synthesis chip with a built-in VCO, the phase discrimination frequency of the step phase-locked loop is selected to be more than 60MHz, and the output frequency of 3-6 GHz is used as a radio frequency signal of a first local oscillation feedback channel frequency mixer.
6. The apparatus of claim 1, wherein a second local oscillator PLL1 generates a second local oscillator signal required by the overall apparatus and provides a 1600MHz frequency reference with low phase noise for the DDS circuit; the DDS circuit generates a sweep frequency signal in a frequency range of 50-100 MHz in a direct digital frequency synthesis mode to provide a low-phase noise phase-locked reference signal for the first local oscillator frequency synthesizer; the first local oscillator frequency synthesizer compares the phase difference of the reference signal and the feedback signal, and outputs error current to the loop filter through the internal charge pump to convert the error current into error voltage to tune the output frequency of the VCO; the loop filter comprises two different loop parameters under a frequency mixing mode and a frequency dividing mode, and the complete machine performs selection control on the loop filter according to the sweep width setting; the broadband VCO selects a frequency band of 6-12 GHz, the directional coupler outputs a VCO signal main circuit to a mixer in a frequency spectrograph radio frequency channel, and an auxiliary circuit is output to a feedback channel of the phase-locked loop.
7. The miniaturized broadband frequency synthesizer according to claim 6, wherein in the feedback channel, a 2-frequency divider converts a local oscillator feedback signal of 6-12 GHz into 3-6 GHz, and the first single-pole double-throw RF switch selects the frequency dividing path or the frequency mixing path according to the host sweep setting; the frequency division path is that 3-6 GHz feedback signals output by the 2-frequency divider generate feedback phase discrimination signals within a range of 50-100 MHz after being subjected to N frequency division by the feedback N-frequency divider, and the feedback phase discrimination signals are fed back to the first local oscillator frequency synthesizer; and the frequency mixing channel is that a 3-6 GHz feedback signal output by the 2 frequency divider is amplified by the feedback amplifier and then used as a local oscillation signal of the frequency mixer, the frequency mixer mixes the 3-6 GHz local oscillation signal of the feedback channel with a radio frequency signal generated by the low-noise stepping phase-locked loop, and an intermediate frequency signal of 50-100 MHz is output and fed back to the first local oscillation frequency synthesizer.
8. A miniaturized wideband frequency synthesizing device as claimed in claim 7, characterized in that the division ratio N of the feedback N-divider is 64.
9. The apparatus of claim 7, wherein the feedback path of the first local oscillator main loop is implemented by combining a frequency division N mode with a frequency mixing mode, the frequency division N mode is implemented when the whole apparatus is set to a large scan width, and the frequency mixing mode is implemented when the whole apparatus is set to a small scan width.
10. The apparatus of claim 9, wherein the frequency sweep function and the small frequency step in the mixing mode are realized by the DDS circuit, and the large frequency step and the low phase noise index are realized depending on the phase discrimination frequency and the phase noise index of the low noise step phase-locked loop; the scanning starting frequency presetting of the frequency mixing mode is realized in an N frequency division mode, after the frequency division mode sets a first local oscillator starting frequency, a single-pole single-throw analog switch at the rear end of a first local oscillator frequency synthesizer is switched off to maintain the current tuning voltage unchanged, and the single-pole single-throw analog switch is switched on after the frequency setting of the DDS and the stepping ring is completed, so that the first local oscillator output frequency can be quickly switched to the set frequency when a first single-pole double-throw radio frequency switch in a channel is switched.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113419111A (en) * | 2021-08-24 | 2021-09-21 | 深圳市鼎阳科技股份有限公司 | Spectrum analyzer and signal scanning method for same |
| CN113489487A (en) * | 2021-06-22 | 2021-10-08 | 中国电子科技集团公司第二十九研究所 | Integrated VCO (voltage controlled oscillator) type phase discriminator and in-loop mixing type phase-locked loop circuit |
| CN117040530A (en) * | 2023-08-01 | 2023-11-10 | 南京威翔科技有限公司 | Broadband frequency synthesis module |
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