JP2004015260A - Evaluation system and evaluation method of rf down converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to evaluate the performance of a RF (radio frequency) down converter itself. <P>SOLUTION: The RF down converter demodulates a RF signal applied with spread spectrum, superimposing a PN (pseudo random noise) code to a carrier wave from a RF signal generator to an IF signal and outputs it. At the same time, the evaluation system evaluates, by delaying the PN code taken from the RF signal generator by means of a delay circuit and outputs it, detecting a carrier component from the output obtained by applying inverse spread spectrum of the delayed PN code and the IF signal inputted into a multiplier, and calculating the C/N ratio. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an RF down converter performance evaluation system and a performance evaluation method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known a technique called spread spectrum in which a digital signal is spread after being spread over a band wider than the original signal by a signal called a spread code, and the original digital signal is restored on the receiving side by the same spread code.
[0003]
This is because it has features such as being able to secure confidentiality, being resistant to noise, and not causing a sudden deterioration in quality even in an overcrowded state, and therefore has a Global Positioning System (GPS). CDMA) or a code division multiple access method (CDMA: Code Division Multiplex Access, hereinafter referred to as CDMA).
[0004]
In such a GPS or CDMA, an RF down converter for converting a spread spectrum RF (Radio Frequency) signal into an IF (Intermediate Frequency) signal of several hundred kHz to several tens MHz suitable for signal processing is usually used. IC is used.
[0005]
As shown in FIG. 8, the RF downconverter IC includes a mixer A1 for downconverting a spread spectrum RF signal into an IF signal, a voltage controlled oscillator (VCO) A2 of a local frequency oscillator, and a minute control unit. And an amplifier A3 for amplifying a signal.
[0006]
When manufacturing and shipping such an RF downconverter IC, performance evaluation is performed. Conventionally, evaluation was performed as follows.
[0007]
That is, as shown in FIG. 9, an RF signal generator B that superimposes a PN (Pseudorandom Noise) code and data on a carrier to spread a spectrum and outputs an RF signal, and the RF downconverter IC to be evaluated include: An arithmetic processing device (DSP: Digital Signal Processor, hereinafter referred to as DSP) usually used in combination with the RF downconverter IC is prepared here for performance evaluation, and the RF signal output from the RF signal generator B is prepared. V1 is actually received by the RF downconverter IC, and the IF signal V2 output from the downconverted IC is processed by the DSP previously connected to the output terminal of the RF downconverter IC, and the reception sensitivity is measured. The performance was evaluated based on the received receiving sensitivity.
[0008]
[Problems to be solved by the invention]
However, the above-described conventional method has a problem as described below.
[0009]
That is, as shown in FIG. 10, the IF signal V2 output from the RF downconverter IC is in a state of being spread in a wide band around the IF signal fIF and buried in noise. Then, as described above, the signal is processed by the DSP, and the measurement is performed. However, this is merely a reception characteristic in a state where the RF downconverter IC and the DSP are combined, and the reception sensitivity varies depending on the DSP. Therefore, the evaluation of the RF downconverter IC alone cannot be performed.
[0010]
That is, when the characteristics of the RF downconverter IC are evaluated, the characteristics of the DSP have been greatly affected in the past.
[0011]
There is no particular problem if the RF down-converter IC is always used in combination with a DSP most suitable for evaluating the IC, but the above-described conventional method is used when evaluating the characteristics of the RF down-converter IC alone. Then, the evaluation may be changed depending on the combination of the RF downconverter IC and the DSP or the individual performance of the DSP.
[0012]
In addition, when the frequency of the IF signal V2 output from the RF downconverter IC is different from the input frequency of the DSP, there is a problem that even the total reception characteristics of the RF downconverter IC and the DSP cannot be measured.
[0013]
An object of the present invention is to provide a performance evaluation system and a performance evaluation method for an RF downconverter that can solve the above problems.
[0014]
Means for Solving the Invention
In order to solve the above problem, according to the present invention, an RF signal generator that outputs a spectrum-spread RF signal in which a PN code is superimposed on a carrier wave, and the RF signal is input and down-converted, An RF down-converter that converts the signal into an IF signal and outputs the signal, a multiplier that multiplies the PN code by the IF signal and performs spectrum despreading, and a spectrum analyzer that detects a carrier component of the IF signal from the output of the multiplier. An evaluation system for an RF downconverter, comprising:
[0015]
In the present invention, the PN code output from the RF signal generator is multiplied by the IF signal.
[0016]
According to the third aspect of the present invention, there is provided a delay circuit having a variable delay amount for delaying the PN code output from the RF signal generator.
[0017]
According to the fourth aspect of the present invention, the RF signal generator superimposes a PN code on a carrier wave and spreads the spectrum to demodulate the RF signal into an IF signal by an RF down converter and outputs the IF signal. The extracted PN code is output after being delayed by a delay circuit, and the delayed PN code and the IF signal are input to a multiplier, and a carrier component is detected by a spectrum analyzer from an output obtained by spectrum despreading. The RF downconverter was evaluated by taking the / N ratio (carrier power to noise power ratio).
[0018]
According to the fifth aspect of the present invention, an RF signal generated by superimposing a PN code and a data signal on a carrier by an RF signal generator and spectrum-spread is converted into an IF signal by an RF down-converter and output. The PN code extracted from the signal generator is output after being delayed by a delay circuit, and the delayed PN code and the IF signal are input to a multiplier, and the frequency component is obtained from an output obtained by spectrum despreading using a spectrum analyzer. The RF down-converter was evaluated by detecting the S / N ratio (signal-to-noise ratio).
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The performance evaluation system for an RF downconverter according to the present embodiment includes an RF signal generator that outputs a spread spectrum RF signal in which a PN code is superimposed on a carrier, and an RF signal that is input and downconverted, and an IF signal An RF down-converter that converts and outputs the IF signal, a multiplier that multiplies the PN code by the IF signal and performs spectrum despreading, and a spectrum analyzer that detects a carrier component of the IF signal from an output of the multiplier. Things.
[0020]
That is, for example, when evaluating an RF down-converter IC that handles a spread-spectrum signal such as a GPS, a spread-spectrum RF signal in which a PN code is superimposed on a carrier wave is output from an RF signal generator and received by the RF down-converter. Then, the signal is converted into an IF signal, and the output is multiplied by the PN code, and only the carrier component of the IF frequency is detected by the spectrum analyzer from the signal output which is subjected to spectrum despreading.
[0021]
By measuring the C / N ratio (carrier power-to-noise power ratio), which is the ratio between the level of the carrier component and the noise level, the RF down-converter IC, which could not be achieved conventionally, can be used regardless of the IF signal. The performance can be evaluated.
[0022]
The PN code input to the multiplier is preferably a PN code extracted from the RF signal generator. In other words, spread spectrum is a method of spreading a digital signal into a band wider than the original signal using a PN code and transmitting the signal, and restoring the original digital signal using the same PN code on the receiving side. This is because the use of the same PN code allows more accurate evaluation.
[0023]
Further, it is more preferable that the apparatus further includes a delay circuit having a variable delay amount for delaying the PN code output from the RF signal generator.
[0024]
In other words, the influence of the delay time generated in the RF downconverter IC can be eliminated by the delay circuit, and the optimal delay amount can be set for the RF downconverter IC to be evaluated, so that the carrier (carrier) after the spectrum despreading is performed. The peak of the component can be raised, and the highest performance level of the RF downconverter can be detected.
[0025]
By the way, according to the preferred RF down converter evaluation system described above, an RF signal generated by superimposing a PN code on a carrier by an RF signal generator and spread spectrum is demodulated into an IF signal by an RF down converter and output. A PN code extracted from the RF signal generator is output after being delayed by a delay circuit, and the delayed PN code and the IF signal are input to a multiplier, and a carrier component is obtained from an output obtained by spectrum despreading to obtain a spectrum. The RF down-converter is evaluated by detecting it with an analyzer and taking the C / N ratio. Alternatively, the following evaluation method may be used.
[0026]
That is, the RF signal generator superimposes a PN code and a data signal on a carrier wave and spreads the spectrum to convert the RF signal into an IF signal by an RF down-converter and outputs the IF signal. The code is delayed by a delay circuit and output. The delayed PN code and the IF signal are input to a multiplier, and a frequency component is detected by a spectrum analyzer from an output obtained by spectrum despreading. The RF downconverter is evaluated by taking the (signal to noise ratio).
[0027]
As described above, the performance of the RF downconverter alone can be evaluated by calculating the ratio between the signal component including the data component and the noise component in the IF frequency carrier component as described above.
[0028]
Hereinafter, the present embodiment will be described more specifically with reference to the drawings.
[0029]
FIG. 1 is a block diagram for briefly explaining an RF down converter evaluation system (hereinafter, simply referred to as an “evaluation system”) A according to the present embodiment.
[0030]
As shown in the figure, the evaluation system A includes an RF signal generator 1 that outputs a spectrum-spread RF signal V11 in which a PN code is superimposed on a carrier wave, receives and inputs the RF signal V11, downconverts the signal, and outputs an IF signal. An IC (hereinafter, referred to as an “RF downconverter”) 2 as an RF downconverter that converts the voltage into V12 and outputs the same, and a delay circuit with a variable delay amount that delays the PN code output V13 from the RF signal generator 1 3, a multiplier 4 for multiplying the IF signal V12 by a PN code as an output V14 passed through the delay circuit 3 and despreading the spectrum, and a carrier wave component of the IF signal from the output V15 from the multiplier 4. And a spectrum analyzer 5 for detection.
[0031]
The RF down-converter 2 is composed of an IC as described in the related art, and as shown in FIG. 8, a mixer A1 for down-converting a spread-spectrum RF signal into an IF signal, and a local frequency oscillator A voltage controlled oscillator A2 and an amplifier A3 for amplifying a small signal are provided.
[0032]
Further, the RF signal generator 1 includes a carrier generation means CWG and a PN code generator PNG for superimposing a PN code on the carrier. The RF signal V11 output from the RF signal generator 1 fRF is a signal that has been spectrum-spread with a PN code, and has frequency components as shown in FIG.
[0033]
Then, the RF signal V11 is down-converted into the IF signal fIF by the RF down converter 2, amplified by the amplifier A3, and the amplified IF signal V12 is input to the multiplier 4. The IF signal fIF is the difference between the frequency of the carrier fRF of the RF signal generator 1 and the local frequency of the RF downconverter 2.
[0034]
Further, only the PN code can be output from the RF signal generator 1, and the output PN code V 13 is input to the delay circuit 3, delayed and output according to the delay time generated in the RF down converter 2, and multiplied. Input to the container 4. Then, the PN code V13 and the IF signal V12 are multiplied by the multiplier 4 so that the spectrum is despread, and is input from the multiplier 4 to the spectrum analyzer 5 as an output V15 of only the frequency component of the IF signal.
[0035]
When the spectrum-despread output V15 is observed by the spectrum analyzer 5, as shown in FIG. 3, the signal is more prominent than the noise level. At this time, the carrier level (C) of the spectrum analyzer 5 and the noise level By measuring the ratio to (N), that is, the C / N ratio, it is possible to evaluate the performance of the RF downconverter 2 alone. Moreover, the evaluation system A has a relatively simple configuration, does not require a special dedicated device, and is easy to introduce.
[0036]
FIG. 4 shows an evaluation system A ′ according to another embodiment. Note that the same components as those of the evaluation system A according to the previous embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0037]
The present embodiment differs from the previous embodiment in that data is superimposed on carrier fRF in RF signal generator 1 '.
[0038]
In this case, when the output V25 after spectrum despreading by the multiplier 4 is observed by the spectrum analyzer 5, as shown in FIG. 5, a data component appears in a frequency component as a carrier component of the IF signal. Again, the signal is more prominent than the noise level. By measuring the ratio of the signal component (S) to the noise component (N), that is, the S / N ratio, the performance of the RF downconverter 2 alone is evaluated. Becomes possible.
[0039]
By the way, the delay circuit 3 in each of the embodiments described above has a variable delay amount for delaying the PN code.
[0040]
This is because the effect of the delay time generated in the RF downconverter 2 can be eliminated by making the delay amount variable. In addition, if the optimum delay amount is appropriately set in the RF downconverter 2, the delay after the spectrum despreading can be reduced. Can be further increased. Therefore, the highest performance level of the RF down converter 2 can be detected.
[0041]
Further, the multiplier 4 in each of the embodiments described above may perform digital processing using an exclusive OR (Exclusive OR) as shown in FIG. 6, or use a double balancer as shown in FIG. Analog processing.
[0042]
【The invention's effect】
The present invention is implemented in the form described above, and has the following effects.
[0043]
(1) According to the first aspect of the present invention, an RF signal generator for outputting a spread spectrum RF signal in which a PN code is superimposed on a carrier wave, and the RF signal is input and down-converted to an IF signal. A configuration comprising: an RF downconverter for converting and outputting; a multiplier for multiplying the PN code by the IF signal to despread the spectrum; and a spectrum analyzer for detecting a carrier component of the IF signal from an output of the multiplier. By using the RF down converter evaluation system described above, the evaluation of the RF down converter alone can be surely performed, and since it is relatively simple, it can be easily introduced.
[0044]
(2) According to the second aspect of the present invention, since the PN code output from the RF signal generator is multiplied by the IF signal, spectrum despreading can be executed accurately.
[0045]
(3) According to the third aspect of the present invention, since the delay circuit having a variable delay amount for delaying the PN code output from the RF signal generator is provided, the delay time generated in the RF down converter is provided. In addition to eliminating the effects of the above-mentioned delay circuit, the optimum amount of delay can be set for the RF downconverter to be evaluated, and the peak of the carrier component after spectrum despreading can be increased. The highest performance level can be detected.
[0046]
(4) According to the fourth aspect of the present invention, an RF signal generated by superimposing a PN code on a carrier by an RF signal generator and spectrum-spread is demodulated into an IF signal by an RF down-converter and output. A PN code extracted from the RF signal generator is output after being delayed by a delay circuit, and the delayed PN code and the IF signal are input to a multiplier, and a carrier component is obtained from an output obtained by spectrum despreading. , And the C / N ratio (carrier power to noise power ratio) is used for the evaluation, so that the RF down converter alone can be reliably evaluated.
[0047]
(5) According to the fifth aspect of the present invention, an RF signal generator superimposes a PN code and a data signal on a carrier wave and spreads the spectrum to convert the RF signal into an IF signal by an RF down-converter and outputs it. On the other hand, the PN code extracted from the RF signal generator is output after being delayed by a delay circuit, and the delayed PN code and the IF signal are input to a multiplier to obtain a frequency from an output obtained by spectrum despreading. Since the components are detected by a spectrum analyzer and evaluated by taking the S / N ratio (signal-to-noise ratio), the evaluation of the RF downconverter alone can be reliably performed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of an evaluation system for an RF downconverter according to the present invention.
FIG. 2 is an explanatory diagram illustrating frequency components of an RF signal output from an RF signal generator.
FIG. 3 is an explanatory diagram showing a signal subjected to spectrum despreading in the first embodiment.
FIG. 4 is a block diagram showing a second embodiment of the evaluation system for the RF downconverter according to the present invention.
FIG. 5 is an explanatory diagram showing a spectrum despread signal according to the second embodiment.
FIG. 6 is an explanatory diagram of an exclusive OR constituting a multiplier.
FIG. 7 is an explanatory diagram of a double balancer constituting a multiplier.
FIG. 8 is a block diagram of an RF down-converter IC.
FIG. 9 is a block diagram showing a conventional RF downconverter IC evaluation system.
FIG. 10 is an explanatory diagram showing an IF signal after down-conversion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 RF signal generator 2 RF down converter 3 Delay circuit 4 Multiplier 5 Spectrum analyzer

Claims (5)

An RF signal generator that outputs a spread spectrum RF signal in which a PN code is superimposed on a carrier, an RF down converter that inputs and downconverts the RF signal, converts the RF signal into an IF signal, and outputs the IF signal; An RF down-converter evaluation system, comprising: a multiplier for multiplying an IF signal to despread a spectrum; and a spectrum analyzer for detecting a carrier component of the IF signal from an output of the multiplier. 2. The evaluation system for an RF downconverter according to claim 1, wherein the PN code output from the RF signal generator is multiplied by the IF signal. 3. The evaluation system for an RF downconverter according to claim 1, further comprising a delay circuit having a variable delay amount for delaying a PN code output from the RF signal generator. The RF signal generator superimposes a PN code on a carrier wave and spreads the spectrum to demodulate an RF signal into an IF signal by an RF down-converter and outputs the same, while delaying the PN code extracted from the RF signal generator by a delay circuit. The delay PN code and the IF signal are input to a multiplier, and a carrier component is detected by a spectrum analyzer from an output obtained by spectrum despreading, and evaluated by taking a C / N ratio. A method for evaluating an RF downconverter, comprising: The RF signal generator superimposes a PN code and a data signal on a carrier wave and converts the spread spectrum RF signal into an IF signal by an RF down-converter and outputs the IF signal. On the other hand, the PN code extracted from the RF signal generator is output. The output is delayed by a delay circuit, the delay PN code and the IF signal are input to a multiplier, and a frequency component is detected from an output obtained by spectrum despreading using a spectrum analyzer to obtain an S / N ratio. A method for evaluating an RF downconverter, wherein the evaluation is performed by the following.

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