JPH0335172A - Network analyzer - Google Patents

Abstract

PURPOSE:To obtain a wide dynamic range which is not limited to the attenuation quantity of an attenuator by reducing the attenuation quantity by a specific quantity and performing reception and detection when the response signal of a circuit to be measured is smaller than a specific level. CONSTITUTION:A test signal generation part 3 outputs a test signal, swept within a specific frequency range with the output signal of a sweep control means 40, to the circuit 1 to be measured and the response signal from the circuit 1 is attenuated by an attenuator 24, converted by a mixer 25 to an intermediate frequency and amplified by a variable gain amplifier 27, and detected by a detecting circuit 30 and displayed on a CRT 14. Here, when the level of the response signal becomes smaller than the specific level, an attenuation quantity switching means 28 outputs a control signal to decrease the attenuation quantity of the attenuator 24 by the specific quantity and a gain switching means 29 varies the gain of the amplifier 27 according to the attenuation quantity of the attenuator 24. Therefore, a low-level signal is received and detected without being attenuated greatly, so a measurement is taken over the wide dynamic range.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field of the Present Invention The present invention relates to a network analyzer for measuring amplitude characteristics and phase characteristics of a circuit under test with respect to frequency.

<Prior art> (Figures 8 to 9) This type of device is used for testing in which the level is kept constant and the frequency range to be measured is swept in order to quickly measure the amplitude characteristics, phase characteristics, etc. with respect to the frequency of the measured object. It has a signal generator that generates a signal, inputs this test #@ signal to the circuit under test, receives and detects the output response signal, and calculates the amplitude and phase between the input and output of the circuit under test at each frequency. It is configured to display phase difference etc. on a cathode ray tube or the like.

FIG. 8 is a block diagram showing the configuration necessary for amplitude measurement of a conventional network analyzer.

The test signal generation section 3 of this network analyzer 2 is
A signal (frequency Fv) from a voltage controlled oscillator (hereinafter referred to as VCO) 4 is frequency-converted by a signal with a frequency F which matches the intermediate frequency of the receiving section 6, which will be described later, to obtain a frequency 1''.
It is configured to output a test signal of v-Fl (or Fv, +Ft) to the circuit under test 1 (5 is a mixer)
.

3 results for the test signal! The output response signal from the lI constant circuit 1 is input to the mixer 9 via an attenuator (hereinafter referred to as ATT) 7 of the receiver 6, converted to an intermediate frequency of "1" by the output signal of the VCO 4, and band limited by the filter 10. The signal is then amplified by an amplifier 11.

Note that 8 is a setting device for manually setting the attenuation amount of the ATT7.

Therefore, this receiving section 6 receives the frequency 1"v of the VCO 4.
Even if the frequency of the test signal changes as the M signal is swept, it will always be tuned to the frequency of the test M signal.

12 is a detection circuit that detects the amplitude level of the signal received and amplified in the receiving section; 13 is a detection circuit that receives the frequency data of the test signal and the amplitude level for each frequency;
This is a display control means for displaying on a CRT (hereinafter referred to as CRT) 14.

15 is the sweep center frequency of the test signal set in advance;
The control means 13 sends a sweep signal corresponding to the sweep step etc. to the VCO 4 and displays the frequency data of the test signal.
This is a sweep control means for sending data to the

When a conventional network analyzer having such a configuration is used to connect a 311-pass type filter as the circuit under test 281 and measure its passband characteristics (selection characteristics), the sweep range including the filter's pass frequency and In addition to setting the sweep step etc. in the sweep control means 15, the attenuation amount of the ATT 7 is set in advance by the setting device 8 so that the level of the output response signal input to the receiving section 6 is below the allowable upper limit level determined by the ability of the mixer 9 etc. After setting, start the test signal sweep (VCO4 sweep).

When the sweep is started, the detection level for each set frequency step is displayed on the CRT 14, as shown in FIG. 9, and the passband characteristic S of this filter is displayed.

Note that in FIG. 9, N is the floor noise level that mainly depends on the input noise of the amplifier 11, and indicates the measurement limit.

However, when measuring a circuit under test that has a large cutoff attenuation, such as a crystal filter, and whose input level is regulated, the ATT7 during sweeping does not reach the maximum output of the output response signal. The amount of attenuation determined by the difference between the level and the allowable upper limit level (No. 91: A of g) is fixed.

For this reason, there is a problem in that, for example, very small level signals near both ends of the pass band of the filter are attenuated by the ATT 7 and become below floor noise, making them impossible to measure.

That is, the measurement dynamic range is greatly limited by the amount of attenuation of the ATT 7, and there is a problem in that the original characteristics (S in FIG. 9) of the circuit under test having a wide dynamic range cannot be fully known.

For measurements with such a wide dynamic range, the sweep frequency is divided into high and low level ranges, and the A
The settings of TT must also be changed in each range.

For this reason, when making additional adjustments to the circuit under test, adjustments must be made while changing the sweep frequency and ATT settings many times, resulting in a very complicated task.

In order to solve this problem, the present invention provides an A
It is an object of the present invention to provide a network analyzer that can perform measurements with good S/N while automatically switching TT depending on the input level.

Means for Solving the Problems> In order to solve the above problems, the network analyzer of the present invention includes a test signal generation circuit that outputs a frequency-sweepable test signal to a circuit under test; a sweep control means that outputs a signal to sweep the test signal over a predetermined frequency range; an attenuator that varies the amount of attenuation by the control signal and attenuates the output response signal from the circuit under test to the test signal; and a signal from the attenuator. a frequency conversion circuit that tunes and receives the test signal by following the frequency sweep change of the test signal and converts it to an intermediate frequency; a variable gain amplifier that amplifies the output signal from the frequency conversion circuit by varying the gain according to a control signal; A detection circuit that detects the signal from the variable amplifier, a display means that displays the output of the detection circuit in correspondence with the frequency of the output response signal, and outputs a control signal when the level of the output response signal becomes lower than a predetermined level. and switching control means for reducing the amount of attenuation of the attenuator by a predetermined amount and changing the gain of the variable gain amplifier in accordance with the amount of attenuation of the attenuator.

Therefore, when the level of the output response signal is lower than a predetermined level, the attenuation amount of the attenuator is reduced by a predetermined amount, so that the signal with a small level is received and detected without being subjected to large attenuation, and the S/ Measurements with a good N and a wide dynamic range can be performed.

Embodiments of the present invention> (Figures 1 to 4) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, this network analyzer 22 is
A frequency-swept test signal is input to the circuit under test 1 from the test signal generating section 3 similar to that described above (FIG. 8); the receiving section 23 receives the output response signal.

24, the input output response signal can be set arbitrarily in 10 dB steps (for example, 0 to 30 dB) according to the attenuation amount setting data.
This is the ATT that attenuates the signal.

25 is a signal from VCO4, and the input signal is set to intermediate frequency Fj.
26 is an intermediate frequency filter.

Reference numeral 27 denotes a variable gain amplifier that amplifies the signal from the intermediate frequency filter 26 within a predetermined gain range (for example, 30 dB to 60 dB>) in 10 dB steps according to gain setting data.

The attenuation A of the ATT 24 and the gain G1 of the variable gain amplifier 27 are switched by data from an attenuation switching means 28 and a gain switching means 29, respectively. Based on the detection level data D1 of 1, switching control as shown in FIG. 2 is performed.

That is, when the first detection level data D1 is 0', AT
The attenuation ff1A of T24 is the maximum (30 dB>, the gain Ql of the variable gain amplifier R27 is the minimum (30 dB>), and the following:
Every time the first detection level data D1 increases by “20”,
Both the attenuation amount A and the gain WG1 are switched to change by QlodB (unchanged when Ds is in the range of 0 to 40)
.

Therefore, the reception gain from the ATT 24 to the variable gain amplifier 27 is G1-A-L, and the input level is 20d.
The reception gain changes every time B changes (however, B is the sum of the conversion loss of the mixer 25, the insertion loss of the intermediate frequency filter 26, etc.).

The detection circuit 30 is configured to have an auto range switching function.

Reference numeral 31 denotes a variable gain amplifier configured in substantially the same manner as the variable gain amplifier 27, and the gain G2 can be changed arbitrarily (for example, from OdB to 100 dB) in 20 dB steps.

32 is a diode detector, 33 is a diode detector 32
A logarithmic converter 34 is an AD converter that converts the output of the logarithmic conversion R33 into a digital value and outputs it as second detection level data D2.

35 compares the second detection level data D2 with a preset upper limit level value Rs (20 dBm) and lower limit level value R2 (OdBm>), and outputs a gain reduction signal when D2 is larger than R1. , D2 is less than R2, the comparison means outputs a gain increased signal.

36 is a range switching means that receives the gain increase signal and gain decrease signal from the comparison means 35 and increases or decreases the gain of the variable gain amplifier 31 in units of 20 dB;
The detection level data Os) is adjusted by II4 so as to match the gain value G2 of the variable gain amplifier 31.

Therefore, this detection circuit 30 has an input level of 20d.
The gain G2 of the variable gain amplifier 31 increases (decreases) every time B increases (decreases).
The range is automatically switched so that the input level decreases (increases), and the linearity part (for example, 0 to 2063 m) of the detection diode 32 detection characteristic is used to maintain linearity over a wide range of input levels. Good detection is performed.

37 is a calculation means for calculating the amplitude level of the output response signal input to the receiving section 23 based on the first and second detection level data D1 and D2.

This calculation means 37 calculates the reception gain (G
1-A-L) is stored in advance, and the level of the output response signal input to the receiving section 23 is determined by combining this reception gain with 02,
Calculated using D].

40 is based on the sweep center frequency data and sweep step data Δf set in advance by the measurement condition setting means 41.
It outputs a sweep signal to the VCO 4 and also sends frequency data of the test signal to the display control 1113.

Next, the operation of measuring the amplitude characteristics of a crystal filter using this network analyzer as the measurement circuit 1 will be described.

The filter passing center frequency Fc1 and the sweep step Δf are set in advance by the measurement condition setting means 41, and the sweep is started from a low frequency.

At this time, the output level of the test signal is fixed to a predetermined level (known) allowed for this crystal filter, and the loss L = 10 dB, R = 20 dBm1R2 = Od
Bm), and 707/IXL/Bell is the output of the intermediate frequency filter 26 and is -140 dBm.

Here, when the frequency of the test signal is at a low frequency fl that deviates from the passing center frequency of the crystal filter, and the level of the output response signal is very small (-120 d Bm), the attenuation ff1A of the ATT 24 of the receiving section 23 is Suppose that 2
0dB1. : If this is set, the level of the output response signal will be attenuated to -140 dBm and input to the mixer 25 for frequency conversion, but this converted output level will be lower than the floor noise level (- 14
0dBm) or less, and the variable gain amplifier 27 outputs 40
A dB amplified noise signal of approximately 100 dBm is input to the detection circuit 30.

In the detection circuit 30, the gain of the variable gain amplifier 31 is increased by the auto range function, and the first detection level data D is
1 becomes "100", and the second detection level data D2 becomes "0".

Therefore, due to a change in the first detection level data D1, the attenuation MA of the ATT24 of the receiving section 23 is switched to 0 dB, and the gain G1 of the variable gain amplifier 27 is switched to 60 dB.

Therefore, the output response signal of -120 dBm is ATT2
4, the frequency is converted by the mixer 25,
A signal of -130 dBm, which is larger than the floor noise, is output from the intermediate frequency filter 26, amplified by 60 dB, and input to the detection circuit 30.

The detection circuit 30 calculates this input level, and displays a detection level -12063m corresponding to the frequency fl on a screen with the frequency as the horizontal axis.

Similarly, the frequency of the test signal is changed to f2 in Δf steps.
, f3, . . . each time the detection level is sequentially switched. However, if the input level of the output response signal exceeds 1100 dBm, the gain of the variable gain amplifier 31 of the detection circuit 30 changes. I? G2 switches from 100dB to 80dB, and the attenuation MA of ATT24 is 10d
B, the gain *G1 of the variable gain amplifier 27 changes to 50 dB.

In this way, as the input level of the output response signal increases, the amount of attenuation of the ATT24 gradually increases as shown in FIG. The maximum level is 10d
In the state of Bm, the first detection level data D] of the detection circuit 30 is 20", and the second detection level data D2 is "O".
At this time, the attenuation MA of the receiving section 23 is 30 dB,
Gain G1 is 30 dB. In this state, the amplifier means 3
7, the detection level is calculated to be 110 dBm, and the CRT
14.

When the frequency of the test signal further increases and the level of the output response signal decreases, contrary to the above operation, the attenuation ff1A of the ATT24 will decrease sequentially, and when the − sweep is completed, the fourth Passband characteristics as shown in the figure will be displayed on the CRT 14.

If the circuit under test 1 is not adjusted, the same display will be displayed in the second and subsequent sweeps, but if adjustments are made to obtain better pass characteristics, especially as shown by the dotted line in Figure 4. Even when adjustments are made to obtain steeper cut-off characteristics and flatter pass characteristics, this can be done accurately and easily without manual switching of the input attenuation amount or switching of the sweep range.

<Other Embodiments> In the above embodiments, the variable gain amplifier 2 of the receiving section 23
7 and the variable gain amplifier 31 of the detection circuit 30 are provided separately, but they may be configured with one variable gain amplifier 45 as shown in FIG.

In this case, the variable gain amplifier 45 is configured so that the gain can be varied from 60 to 130 dB in 10 dB steps, and the gain setting data G3 shown in FIG. The output gain switching means 46 can perform almost the same operation as described above.

Further, in the above embodiment, the receiving unit 23 is configured to perform frequency conversion only once, but this does not limit the present invention, and the receiving unit 23 is configured to perform frequency conversion two or more times. The present invention can also be applied in exactly the same way.

Further, the configuration of the detection circuit 30 is not limited to the present invention, and a detection circuit having another configuration may be used.

Furthermore, in the embodiment described above, the attenuation of the ATT 24 and the gain of the variable gain amplifier 27 are both variable in four steps in opposite directions in 10 dB steps, but in order to simplify switching, they are variable in two steps in 20 dB steps. Alternatively, the attenuation amount and gain may be varied in the same direction, in which the gain is constant (in this case, the gain of the receiving section is approximately constant regardless of the input level). .

Furthermore, in the embodiment described above, the receiving section 23 was configured to receive the same frequency as the frequency of the test signal for the circuit under test 1, but in the case where the circuit under test 1 has a frequency conversion section. The receiving frequency of the receiving section may be offset to the corresponding frequency range, and the present invention is not limited to the case where the test signal frequency and the frequency of the output response signal are configured to match. .

Further, in the embodiment described above, the detection circuit 30 was used as means for detecting the input level of the output response signal in order to control the attenuation amount of the ATT 24 and the gain of the variable gain amplifier 27, but as shown in FIG. Alternatively, a level detection means 47 for detecting the input level of the output response signal from the output of the variable gain amplifier 27 may be provided separately from the detection circuit 30, and the ATT 24 and the variable gain amplifier 27 may be controlled by this detection signal.

Further, in the above embodiment, the loss f) of the receiving section 23 is fixed, but the loss f) for each input frequency is measured in advance and stored in the calculation means 37, and this loss f) is read out. More accurate measurement is possible if the level calculation is performed for each frequency.

<Effects of the Present Invention> As described above, the network analyzer of the present invention reduces the attenuation amount by a predetermined amount when the level of the output response signal @ from the circuit under test is smaller than a predetermined level, and performs reception detection. As a result, a wide measurement dynamic range that is not limited by the attenuator reduction Wffi can be obtained, and test and adjustment of circuits under test with a wide dynamic range such as crystal filters can be performed without switching the sweep frequency range. It can be done quickly and easily.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining switching operations of main parts of the embodiment. FIG. 3 is a diagram showing a change in attenuation amount with respect to the input level of a main part of one embodiment, and FIG. 4 is a diagram showing a display of measurement results of one embodiment. FIG. 5 is a block diagram of main parts showing another embodiment of the present invention,
FIG. 6 is a diagram for explaining the operation of FIG. 5, and FIG. 7 is a block diagram of main parts showing another embodiment of the present invention. FIG. 8 is a block diagram showing a conventional device, and FIG. 9 is a diagram showing a display of measurement results of the conventional @ position. 1... Circuit under test, 3... Test signal generation section, 13... Display control means, 22...
・Network analyzer, 24...attenuator,
25... Mixer, 27... Variable gain amplifier, 28... Attenuation amount switching means, 29...
...Gain switching means, 30...Detection circuit, 40.
...Sweep control means. Fig. 2 Fig. 3 (dBm) Fig. 4 Fig. 6 Fig. 2 Hand Mne 01 original (spontaneous) 6 windows August 7, 1989

Claims (1)

[Scope of Claims] A test signal generation circuit that outputs a frequency-sweepable test signal to a circuit under test, and a sweep control means that outputs a sweep signal to the test signal generation circuit to sweep the test signal within a predetermined frequency range. an attenuator whose attenuation amount is varied by a control signal to attenuate an output response signal from the circuit under test in response to the test signal; and a signal from the attenuator is tuned to follow a frequency sweep change of the test signal. a frequency conversion circuit that receives the signal and converts it to an intermediate frequency; a variable gain amplifier that amplifies the output signal from the frequency conversion circuit by varying the gain according to a control signal; and a detection circuit that detects the signal from the variable gain amplifier. , display means for displaying the output of the detection circuit in association with the reception frequency of the output response signal; and when the level of the output response signal becomes lower than a predetermined level, outputting a control signal to attenuate the attenuator. 1. A network analyzer comprising switching control means for reducing the amount of attenuation by a predetermined amount and changing the gain of the variable gain amplifier in accordance with the amount of attenuation of the attenuator.