CN105515693A - Wideband measurement method for dual-channel wideband receiver of vector network analyzer - Google Patents

Abstract

The invention relates to a wide-band measurement method for a dual-channel wide-band receiver used in a vector network analyzer, which solves the problem of introducing a large amount of noise due to the down-conversion of the low-frequency end in the wide-band measurement, causing the dynamic range of the low-frequency band to fail to be consistent with that of the high-frequency band . In the low frequency band (within 10MHz), use ADC to directly sample, so that the vector network analyzer can obtain a higher dynamic range in the low frequency band; Perform ADC sampling, which improves the range that can be measured in high frequency bands. Through the low-band channel and the high-band channel, the vector network analyzer can have a wide frequency range.

Description

Wideband Measurement Methods for Dual Channel Wideband Receivers for Vector Network Analyzers

technical field

The invention belongs to the technical field of vector network analysis, and specifically relates to a wideband measurement method for a dual-channel wideband receiver of a vector network analyzer.

Background technique

With the development of measurement technology, the frequency range required to be tested is getting wider and wider, and the requirements for dynamic range in a wide frequency band are getting higher and higher. This requires a vector network analyzer to be able to test lower frequencies and higher frequencies at one time. Frequency, while testing a wide frequency range, it is necessary to ensure the consistency of the test dynamic range.

The traditional vector network analyzer basically uses the full-band mixing mode to realize the receiver solution. In the whole receiver frequency band, the signal passes through the low-noise amplifier and slope attenuator of the RF front-end, and is transformed into the RF signal required by the mixer. , mix with the local oscillator signal provided by the vector network analyzer in the mixer, and generate the required fixed intermediate frequency signal through a down-conversion. The automatic gain control circuit selectively amplifies the intermediate frequency signal, and then quantizes it sampling. This solution cannot meet the needs of broadband testing.

The existing solution mainly implements the receiver solution through the full-band mixing mode, which cannot make the vector network analyzer perform high-frequency and low-frequency tests at the same time, mainly manifested in the following points:

1. The dynamic range of the low-frequency band is small: because the low-frequency band also adopts the frequency mixing scheme, due to the limitation of the characteristics of the mixer itself and the deterioration of the phase noise of the low-frequency local oscillator signal, the sensitivity of the RF receiving end of the receiver is reduced, causing the low frequency of the vector network analyzer. Deterioration of band dynamic range;

2. Low receiver isolation: Since the low-frequency band and high-frequency band share the same low-noise amplifier and slope attenuator, the receiver has different isolation in different frequency bands, which cannot meet the consistency of measurement;

3. The low-frequency signal interferes with the intermediate-frequency sampling signal: when the low-frequency signal is mixed, because the tested low-frequency signal is very similar to the frequency band of the sampled intermediate-frequency signal, the low-frequency signal received by the RF terminal interferes with the intermediate-frequency signal. quality, thus affecting the low frequency test results.

Contents of the invention

The purpose of the present invention is in order to overcome the above-mentioned defect that exists in the prior art, provide a kind of broadband measurement method that the present invention proposes a kind of dual-channel broadband receiver that is used for vector network analyzer, has solved in broadband measurement because low frequency A large amount of noise is introduced due to down-conversion at the end, resulting in the dynamic range of the low-frequency band being unable to be consistent with that of the high-frequency band. In the low frequency band (within 10MHz), use ADC to directly sample, so that the vector network analyzer can obtain a higher dynamic range in the low frequency band; Perform ADC sampling, which improves the range that can be measured in high frequency bands. Through the low-band channel and the high-band channel, the vector network analyzer can have a wide frequency range.

In order to achieve the above object, the wideband measurement method of the dual-channel wideband receiver used for the vector network analyzer proposed by the present invention may further comprise the steps:

Step 1: The radio frequency signal RF enters the receiver through the radio frequency front-end circuit, and enters the low frequency channel and the high frequency channel respectively through the power divider. The low-frequency channel directly enters the 2-to-1 switch, and the high-frequency channel enters the 2-to-1 switch after processing and mixing;

Step 2: The FPGA channel control circuit judges the current signal channel to be sampled, and controls the 2-to-1 switch to select the required channel;

Step 3: The signal selected by the 2-to-1 switch enters the A/D converter for sampling processing. This process adopts over-sampling technology, and the fixed sampling frequency is 60MHz.

In the above technical solution, in the first step, the low-frequency channel and the high-frequency channel obtain sampleable intermediate-frequency signals in different ways, the low-frequency channel is directly sampled, and the high-frequency channel is subjected to down-conversion to obtain an intermediate-frequency signal for sampling, realizing The function of the wideband receiver of the vector network analyzer.

In the above technical solution, in the step 2, the FPGA channel control circuit controls the channel where the vector network analyzer receiver is currently located, realizing the automatic control of channel selection, increasing the distance between the low frequency channel and the high frequency channel isolation.

In the above technical solution, in the step 3, the oversampling processing technology is adopted, and the fixed sampling frequency is 60MHz, which realizes the unification of the sampling frequency of the two channels, improves the bandwidth processing gain, and ensures the consistency of the dynamic range between the two channels sex.

The vector network analyzer needs a very wide frequency band during measurement, and the vector network analyzer is required to be able to test lower frequencies and higher frequencies at one time. The current vector network analyzer uses down-conversion technology when testing low-frequency signals. A lot of noise, the low frequency band cannot achieve the same dynamic range as the high band, and the compliance test cannot be satisfied during the test. Compared with the prior art scheme, the present invention has the following beneficial effects:

1. The frequency range of the vector network analyzer receiver is improved, and the low-frequency channel is directly sampled to ensure the sensitivity of the low-frequency end of the receiver; the high-frequency channel is cascaded and down-converted by multi-stage amplifiers to achieve high gain and greater dynamic range;

2. Channel automatic identification control, adding FPGAFPGA channel control circuit and 2-to-1 switch to realize automatic identification of low-frequency channels and high-frequency channels, and the introduction of 2-to-1 switch increases the isolation between the two channels;

3. The radio frequency circuit board scheme is adopted, the structure is simple and easy to use, and the anti-interference ability is strong.

Description of drawings

Fig. 1 is a schematic diagram of a dual-channel broadband receiver applied to a vector network analyzer according to the present invention.

detailed description

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

As shown in Figure 1, the schematic diagram of a dual-channel broadband receiver applied to a vector network analyzer is composed of three core circuits: a radio frequency front-end receiving circuit, a digital sampling and intermediate frequency processing circuit, and an FPGA channel control circuit. The RF front-end receiving circuit is used to receive and process the RF signal RF received by the test port of the vector network analyzer; the A/D converter circuit is used to convert the processed RF signal RF into a digital signal; the FPGA channel control circuit is used to The signal frequency band of the test port of the network analyzer automatically selects the required channel;

2. The RF front-end receiving circuit is used to process the received RF signal RF, including low-frequency channels and high-frequency channels. The radio frequency signal RF is processed by the first-stage low-noise amplifier, and enters the low-frequency channel or high-frequency channel at the power divider. The frequency band of the low-frequency channel is 100kHz to 10MHz, and the low-frequency signal passes through the low-frequency low-noise amplifier and low-pass filter and directly enters the 2-to-1 switch; the frequency band of the high-frequency channel is 10MHz to 8.5GHz, and the signal passes through the second-stage low-noise amplifier and slope attenuation The device enters the mixer and mixes with the local oscillator signal L0. The frequency difference between the radio frequency signal RF and the local oscillator signal L0 is 7.6MHz, so the intermediate frequency sampling signal of 7.6MHz is obtained after mixing, and enters the 2-to-1 switch.

3. The FPGA channel control circuit is used to select the signal in the low frequency channel or the high frequency channel. The FPGA channel control circuit receives the RF frequency band judgment signal from the upper computer, and controls the 2-to-1 switch to select the corresponding channel. When the signal is from 100kHz to 10MHz, the 2-to-1 switch selects the low-frequency channel, and the high-frequency channel is in a high isolation state; when the signal is from 10MHz to 8.5GHz, the 2-to-1 switch selects the high-frequency channel, and the low-frequency channel is in the High isolation status. The vector network analyzer realizes the separation of low-frequency signals and high-frequency signals through the FPGA channel control circuit, which increases the isolation of the whole machine.

4. The digital sampling and intermediate frequency processing circuit is used for sampling and processing the intermediate frequency signal from 100kHz to 10MHz in the 2-to-1 switch. The signal from 100kHz to 10MHz in the low frequency channel is directly sampled and processed; the 7.6MHz intermediate frequency signal obtained after down-conversion is sampled and processed in the high frequency channel from 10MHz to 8.5GHz. For the low-frequency channel and the high-frequency channel, the sampling frequency is uniformly adopted at 60MHz, and the A/D converter works in an oversampling state, which improves the bandwidth processing gain and improves the dynamic range at the same time. Perform digital down-conversion technology on the sampled signal to separate I and Q signals, which introduces lower noise than analog down-conversion technology.

The wideband measurement method for the two-channel wideband receiver of the vector network analyzer in Fig. 1 includes the following steps:

Step 1: The radio frequency signal RF enters the receiver through the radio frequency front-end circuit, and enters the low frequency channel and the high frequency channel respectively through the power divider. The low-frequency channel directly enters the 2-to-1 switch, and the high-frequency channel enters the 2-to-1 switch after processing and mixing. The low-frequency channel and the high-frequency channel obtain sampleable intermediate frequency signals in different ways. The low-frequency channel is directly sampled, and the high-frequency channel is subjected to down-conversion to obtain an intermediate-frequency signal for sampling, realizing the function of a vector network analyzer broadband receiver.

Step 2: The FPGA channel control circuit judges the signal channel that needs to be sampled currently, and controls the 2-to-1 switch to select the required channel. The FPGA channel control circuit controls the current channel of the vector network analyzer receiver, realizes the automatic control of channel selection, and increases the isolation between the low-frequency channel and the high-frequency channel.

Step 3: The signal selected by the 2-to-1 switch enters the A/D converter for sampling processing. This process adopts over-sampling technology, and the fixed sampling frequency is 60MHz. The over-sampling processing technology is adopted, and the fixed sampling frequency is 60MHz, which realizes the unification of the sampling frequencies of the two channels, improves the bandwidth processing gain, and ensures the consistency of the dynamic range between the two channels.

The invention solves the problem that the dynamic range of the low frequency band cannot be consistent with that of the high frequency band due to the introduction of a large amount of noise due to the down conversion of the low frequency end in the broadband measurement. In the low frequency band (within 10MHz), use ADC to directly sample, so that the vector network analyzer can obtain a higher dynamic range in the low frequency band; Perform ADC sampling, which improves the range that can be measured in high frequency bands. Through the low-band channel and the high-band channel, the vector network analyzer can have a wide frequency range.

The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims (4)

1. a kind of broadband measurement method for the dual-channel wideband receiver of vector network analyzer, is characterized in that, may further comprise the steps: Step 1: The radio frequency signal RF enters the receiver through the radio frequency front-end circuit, and enters the low frequency channel and the high frequency channel respectively through the power divider. The low-frequency channel signal directly enters the 2-to-1 switch, and the high-frequency channel signal enters the 2-to-1 switch after processing and mixing; Step 2: The FPGA channel control circuit judges the current signal channel to be sampled, and controls the 2-to-1 switch to select the required channel; Step 3: The signal selected by the 2-to-1 switch enters the A/D converter for sampling processing. This process adopts over-sampling technology, and the fixed sampling frequency is 60MHz. 2. according to claim 1, is used for the broadband measurement method of the dual-channel broadband receiver of vector network analyzer, it is characterized in that: in described step 1, described low-frequency channel and high-frequency channel obtain sampleable through different modes The intermediate frequency signal, the low frequency channel signal is directly sampled, and the high frequency channel signal is sampled by the intermediate frequency signal after down conversion, realizing the function of the wideband receiver of the vector network analyzer. 3. according to claim 1, is used for the broadband measurement method of the dual-channel wideband receiver of vector network analyzer, it is characterized in that: in described step 2, described FPGA channel control circuit controls vector network analyzer receiver current place The channel at the place realizes the automatic control of channel selection and increases the isolation between the low frequency channel and the high frequency channel. 4. according to claim 1, is used for the broadband measuring method of the dual-channel wideband receiver of vector network analyzer, it is characterized in that: in described step 3, described adopting oversampling processing technique, fixed sampling frequency is 60MHz, realizes It unifies the sampling frequency of the two channels, improves the bandwidth processing gain, and ensures the consistency of the dynamic range between the two channels.