CN201887866U - Circuit for expanding frequency of signal level meter - Google Patents

Circuit for expanding frequency of signal level meter Download PDF

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Publication number
CN201887866U
CN201887866U CN2010202420936U CN201020242093U CN201887866U CN 201887866 U CN201887866 U CN 201887866U CN 2010202420936 U CN2010202420936 U CN 2010202420936U CN 201020242093 U CN201020242093 U CN 201020242093U CN 201887866 U CN201887866 U CN 201887866U
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China
Prior art keywords
circuit
frequency
signal
radio
switch
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Expired - Fee Related
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CN2010202420936U
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Chinese (zh)
Inventor
倪志伟
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DELI ELECTRONIC INSTRUMENT Co Ltd TIANJIN CITY
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DELI ELECTRONIC INSTRUMENT Co Ltd TIANJIN CITY
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Abstract

The utility model relates to signal level meters, in particular to a circuit for expanding frequency of a signal level meter, which a mixer circuit for expanding the frequency of the signal level meter, and comprises a radio frequency switch I, a frequency preselection circuit, a local oscillator, a mixer circuit, a radio frequency switch IV and a television tuner, wherein the radio frequency I in the circuit is in a synchronous match relationship with the radio frequency switch IV, a signal channels are selected by a control software according to needs, the signal channels are divided into a direct signal channel and a mixer signal channel, and the selected signals enter into the television tuner. The traditional circuit is highly integrated by adopting the circuit, so that the space of a printed circuit board is saved, the circuit adapts to the development of a measuring instrument in miniaturization, the cost and the power consumption are greatly lowered, the coefficient of the difficulty of the technology is lowered, and the circuit is easy to realize; the circuit occupies less space of the printed circuit board, and simultaneously, the frequency conversion of two frequency ranges can be completed through a simple mixer circuit, so that the circuit is greatly helpful to the development of hand hold test equipment.

Description

A kind of circuit that is used for spread signal level meter frequency
Technical field
The present invention relates to signal level meter, specifically, is a kind of mixting circuit that is used for spread signal level meter frequency.
Background technology
Cable TV (CATV) signal level meter is one of most basic tester in the CATV system testing, and it mainly measures the index such as frequency, level of cable TV signal.And requirements such as, low cost simple and easy in order to satisfy, on circuit design to adopt TV tuner be the scheme of core receiving circuit more.TV tuner is commonly called as tuner, is the important devices in the television receive terminal, adopts the superheterodyne mode, and received signal is converted to television image and audio signal.Signal level meter is converted to DC level by demodulation circuit of intermediate frequency with image and audio signal again, finishes test request.
The frequency coverage of TV tuner is 46MHz~870MHz, and this scope is called downstream signal in the CATV signal, comprises all television channels.Yet, the reverse back transmission band of user terminal, frequency range is the upward signal of 5MHz~65MHz, also is the scope that the level signal table must cover.Simultaneously, its frequency coverage of CATV system of North America is up to 1000MHz.So in order to satisfy more vast market demand, signal level meter will be finished the 5MHz~46MHz outside the TV tuner frequency coverage and the measurement index requirement of two frequency ranges of 870MHz~1000MHz on circuit design.
Carrying out mixing respectively by two mixting circuits, above-mentioned two frequency ranges are dropped in the TV tuner frequency coverage, is the method for generally taking on the circuit design.Need two mixting circuits to finish frequency conversion work before.
With in the quasi-instrument, also abandon TV tuner abroad, oneself designs the scheme of superheterodyne receiver.The advantage of this scheme is not limited by extraneous device, free setpoint frequency coverage, and also speed is fast, the precision height.But its complex circuit designs, the cost height, it is big to take up room, and is unfavorable for the miniaturization development of instrument.
Summary of the invention
The purpose of this invention is to provide a kind of circuit that is used for spread signal level meter frequency, can use a mixting circuit to satisfy the frequency conversion demand of two frequency ranges.
A kind of circuit that is used for spread signal level meter frequency comprises: radio-frequency (RF) switch one, frequency preselection circuit, local oscillation circuit, mixting circuit, radio-frequency (RF) switch four, TV tuner; Radio-frequency (RF) switch one is synchronous corresponding relation with radio-frequency (RF) switch four in the circuit, selects signalling channel by Control Software as required, and signalling channel is divided into direct channel and mixing channel; Signal after the selection enters TV tuner.Schematic diagram such as Fig. 1.
Described frequency preselection circuit comprises: radio-frequency (RF) switch two, radio-frequency (RF) switch three, low pass filter LPF, high pass filter HPF; Select to need the radiofrequency signal of mixing to enter radio-frequency (RF) switch two by radio-frequency (RF) switch one; Radio-frequency (RF) switch two and radio-frequency (RF) switch three are synchronous corresponding relation, when needs to 5MHz~when the 46MHz signal carries out mixing, select the RF1 port of radio-frequency (RF) switch 2 by Control Software, make signal enter low pass filter LPF and carry out filtering, select the RF1 port of the radio-frequency (RF) switch three of correspondence with it by Control Software, make filtered signal send into mixting circuit; When needs to 870MHz~when the 1000MHz signal carries out mixing, select the RF2 port of radio-frequency (RF) switch two by Control Software, make signal enter high pass filter HPF and carry out filtering, select the RF2 port of the radio-frequency (RF) switch 3 of correspondence with it, make filtered signal send into mixting circuit by Control Software.
Low pass filter LPF allows that the signal of 5MHz~46MHz passes through, and the signal that blanketing frequency is higher than 46MHz passes through; High pass filter HPF allows that the signal of 870MHz~1000MHz passes through, and the signal that blanketing frequency is lower than 870MHz passes through.Schematic diagram such as Fig. 2.
Described local oscillation circuit is made up of chip ADF4360-7 and peripheral circuit, for mixting circuit provides local oscillation signal.
Described mixting circuit comprises: circuit chip LT5560; Input transformer one, impedance matching circuit one; Impedance matching circuit two, output transformer two; As Fig. 4, in the mixting circuit: 1,8 pins of local oscillation signal connection circuit chip LT5560; Radio-frequency input signals connects input transformer one, passes through impedance matching circuit one again, 3,4 pins of connection circuit chip LT5560; Output signal after the mixing through impedance matching circuit two, connects output transformer two outputs by 5,6 pins of circuit chip LT5560 again.
In the described local oscillation circuit: produce local oscillation signal by synthesizer chip ADF4360-7; 16 pins of ADF4360-7 connect the TCXO oscillator, provide reference clock by the TCXO oscillator; The ADF4360-7 chip is constituted the VCO circuit and is produced centre frequency by the external inductance of 9,10 pins, is made by the phase-locked loop circuit of chip ADF4360-7 by software control and exports the local frequency that needs; 24 pins of chip ADF4360-7 are exported phase-locked voltage through loop filter circuit, and radio-frequency component in the filtering voltage and noise go to control the frequency of VCO circuit by 7 pins inputs, and it is locked on the required local frequency; 4,5 pins of chip ADF4360-7 are signal output, suppress harmonic wave by filter circuit, for mixting circuit provides local oscillation signal.Schematic diagram such as Fig. 3.
Described TV tuner is the core receiving device of signal level meter, adopts the superheterodyne mode, and input signal is converted to image, audio signal.
Traditional phase-locked loop circuit generally is made up of frequency-dividing counter, voltage controlled oscillator (VCO) and buffer, its shortcoming be to use device many, take up room big, circuit complexity is high, poor reliability or the like.ADF4360-7 is an integrated integer-N synthesizer and voltage controlled oscillator (VCO) chip, can select the local oscillation signal frequency in the broadband reference frequency output of 350MHz~1800MHz.Its advantage is that cost is low, and is low in energy consumption, and the integrated level height has reduced technical difficulty, saved the printed board space, adapts to the development of measuring instrument miniaturization.And the broadband frequency synthesizer system also selects to provide maximum flexibility for the frequency of local oscillation signal.
Circuit chip LT5560 is an a kind of pair of balance active mixer, adopts the manufacturing of high frequency bipolar technology, has big bandwidth and low-down power consumption.All signal ports can be from almost being that DC works in the frequency range of 4GHz, for up-conversion and down-conversion applications provide convenience.This circuit is used this characteristic just, and to exceeding two frequency ranges of TV tuner frequency coverage, promptly 5MHz~65MHz, 870MHz~1000MHz carry out upper and lower frequency conversion respectively.
The IN of LT5560 chip, OUT and LO port all are the difference ports, to realize optimal performance.Input signal becomes differential signal by input transformer one with single-ended signal, and impedance matching circuit one carries out the impedance matching of port according to incoming frequency, obtains maximum gain.At high-frequency signal big differential loss is arranged in signalling channel, bias toward in the circuit design frequency range of 870MHz~1000MHz is carried out impedance matching, make two frequency conversion frequency ranges can obtain identical gain.Output signal is finished the conversion that differential signal becomes single-ended signal through impedance matching circuit two by output transformer two.Also be to bias toward the high-frequency signal after the mixing is carried out impedance matching in the circuit design, to obtain gain preferably.
The invention has the beneficial effects as follows:
1) in the past traditional circuit has carried out highly integratedly, has saved the printed board space, adapts to the development of measuring instrument miniaturization, and greatly reduces cost and power consumption, has reduced the technical difficulty coefficient, is easy to realize:
2) LT5560 is active mixing chip, with passive mixing chip relatively, have that volume is little, gain is high, the local oscillation signal input range is little, local oscillator is revealed and suppressed advantages of higher;
3) the local oscillation circuit device is few, cost is low, and circuit need not adjusted, and former phase-locked loop circuit and voltage controlled oscillator all is integrated in the chip, thereby greatly reduces the failure rate of cost and debugging, is applicable to batch process;
4) in the printed board space that takies seldom, by an easy mixting circuit, can finish frequency conversion conversion to two frequency ranges, development is very helpful to the hand-hold type testing equipment.
Description of drawings
Fig. 1 is the circuit theory diagrams that are used for spread signal level meter frequency of the present invention
Fig. 2 is the schematic diagram of the frequency preselection circuit of circuit of the present invention
Fig. 3 is the schematic diagram of the local oscillation circuit of circuit of the present invention
Fig. 4 is the schematic diagram of the mixting circuit of circuit of the present invention
Embodiment
Embodiment 1
Use mixting circuit of the present invention to be applied in the television signal level table, make it be applicable to the signal measurement of 5MHz~1000MHz.
As Fig. 1,2,3,4:
● the radio-frequency input signals of 5MHz~1000MHz connects radio-frequency (RF) switch one, and radio-frequency (RF) switch one is synchronous corresponding relation with radio-frequency (RF) switch four, selects signalling channel by Control Software.Select direct channel when measuring 46MHz~870MHz signal, be converted to image, audio signal by TV tuner.
● select the mixing channel when measuring 870MHz~1000MHz signal, signal enters the frequency preselection circuit and connects radio-frequency (RF) switch two.RF2 port by Control Software selection radio-frequency (RF) switch two makes signal enter the high pass filter that cut-off frequency is 870MHz (HPF)
Carry out filtering, select the RF2 port of the radio-frequency (RF) switch 3 of correspondence with it, make filtered signal send into mixting circuit by Control Software.
● 16 pins of chip ADF4360-7 connect 10MHz TCXO oscillator, and reference clock is provided.9,10 pins of ADF4360-7 connect the external inductance of 10nH and constitute the VCO circuit, produce the 600MHz centre frequency.By the phase-locked loop circuit output 560MHz local frequency of software control chip ADF4360-7, phase-locked voltage is imported by 7 pins behind filtering radio-frequency component and the noise through the 24 pins output of loop filter circuit by chip.4,5 pins of ADF4360-7 are by the harmonic wave of filter circuit inhibition 560MHz, for mixting circuit provides local oscillation signal.
● frequency is 1,8 pins that the local oscillation signal of 560MHz meets chip LT5560, is the difference input mode.870MHz~1000MHz signal is converted to differential signal by transformer, connects 3,4 pins of LT5560 through impedance matching circuit.290MHz after the mixing~440MHz output signal by 5,6 pins of chip LT5560, is converted to single-ended signal by transformer again through impedance matching circuit.
● the 290MHz after the mixing~440MHz signal connects radio-frequency (RF) switch four, enters TV tuner by software control and is converted to image, audio signal.
● when measuring 5MHz~46MHz signal, select low pass filter by software control in the frequency preselection circuit, other circuit controls are identical with 870MHz~1000MHz signal.

Claims (6)

1. a circuit that is used for spread signal level meter frequency is characterized in that, comprising: radio-frequency (RF) switch one, frequency preselection circuit, local oscillation circuit, mixting circuit, radio-frequency (RF) switch four, TV tuner; Radio-frequency (RF) switch one is synchronous corresponding relation with radio-frequency (RF) switch four in the circuit, and signalling channel is divided into direct channel and mixing channel.
2. the circuit that is used for spread signal level meter frequency as claimed in claim 1 is characterized in that, described frequency preselection circuit comprises: radio-frequency (RF) switch two, radio-frequency (RF) switch three, low pass filter LPF, high pass filter HPF; Select to need the radiofrequency signal of mixing to enter radio-frequency (RF) switch two by radio-frequency (RF) switch one; Radio-frequency (RF) switch two and radio-frequency (RF) switch three are synchronous corresponding relation,
When needs to 5MHz~when the 46MHz signal carries out mixing, select the RF1 port of radio-frequency (RF) switch two, make signal enter low pass filter LPF and carry out filtering, select the RF1 port of corresponding with it radio-frequency (RF) switch three, make filtered signal send into mixting circuit;
When needs to 870MHz~when the 1000MHz signal carries out mixing, select the RF2 port of radio-frequency (RF) switch two, make signal enter high pass filter HPF and carry out filtering, select the RF2 port of corresponding with it radio-frequency (RF) switch three, make filtered signal send into mixting circuit.
3. the circuit that is used for spread signal level meter frequency as claimed in claim 1 is characterized in that described local oscillation circuit is made up of chip ADF4360-7 and peripheral circuit, for mixting circuit provides local oscillation signal.
4. the circuit that is used for spread signal level meter frequency as claimed in claim 1 is characterized in that, described mixting circuit comprises: circuit chip LT5560; Input transformer one, impedance matching circuit one; Impedance matching circuit two, output transformer two; In the mixting circuit: 1,8 pins of local oscillation signal connection circuit chip LT5560; Radio-frequency input signals connects input transformer one, passes through impedance matching circuit one again, 3,4 pins of connection circuit chip LT5560; Output signal after the mixing through impedance matching circuit two, connects output transformer two outputs by 5,6 pins of circuit chip LT5560 again.
5. the circuit that is used for spread signal level meter frequency as claimed in claim 3 is characterized in that, in the described local oscillation circuit: produce local oscillation signal by synthesizer chip ADF4360-7; 16 pins of ADF4360-7 connect the TCXO oscillator, provide reference clock by the TCXO oscillator; The ADF4360-7 chip is constituted the VCO circuit and is produced centre frequency by the external inductance of 9,10 pins, exports the local frequency that needs by the phase-locked loop circuit of chip ADF4360-7; 24 pins of chip ADF4360-7 are exported phase-locked voltage through loop filter circuit, and radio-frequency component in the filtering voltage and noise go to control the frequency of VCO circuit by 7 pins inputs, and it is locked on the required local frequency; 4,5 pins of chip ADF4360-7 are signal output, suppress harmonic wave by filter circuit, for mixting circuit provides local oscillation signal.
6. the circuit that is used for spread signal level meter frequency as claimed in claim 1 is characterized in that, described TV tuner is the core receiving device of signal level meter, adopts the superheterodyne mode, and input signal is converted to image, audio signal.
CN2010202420936U 2010-06-30 2010-06-30 Circuit for expanding frequency of signal level meter Expired - Fee Related CN201887866U (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103595940A (en) * 2013-10-29 2014-02-19 江苏绿扬电子仪器集团有限公司 Circuit system for digital television local oscillator signals
CN106896268A (en) * 2015-12-18 2017-06-27 苏州普源精电科技有限公司 A kind of frequency expansion device, the spectrum analyzer for possessing spread spectrum function
CN109120261A (en) * 2017-06-26 2019-01-01 北京普源精电科技有限公司 A kind of frequency expansion device and radio-frequency signal source

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103595940A (en) * 2013-10-29 2014-02-19 江苏绿扬电子仪器集团有限公司 Circuit system for digital television local oscillator signals
CN106896268A (en) * 2015-12-18 2017-06-27 苏州普源精电科技有限公司 A kind of frequency expansion device, the spectrum analyzer for possessing spread spectrum function
CN109120261A (en) * 2017-06-26 2019-01-01 北京普源精电科技有限公司 A kind of frequency expansion device and radio-frequency signal source
CN109120261B (en) * 2017-06-26 2023-09-26 北京普源精电科技有限公司 Frequency expansion device and radio frequency signal source

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CF01 Termination of patent right due to non-payment of annual fee

Granted publication date: 20110629

Termination date: 20170630

CF01 Termination of patent right due to non-payment of annual fee