JPH0720169A - Spectrum analyzer with built-in tracking generator - Google Patents

Abstract

PURPOSE:To eliminate a signal source which is leaked to the side of an IF part and to measure a weak signal by a method wherein two oscillators are installed, they are mixed and a required TG (tracking-generator) output frequency is obtained. CONSTITUTION:This constitution is provided with a synthesizer 14 which sweeps a frequency and with a mixer 12 which mixes the synthesizer 14 with a received signal. In addition, mixers 18, 16 which mix the synthesizer 14 with fixed oscillators 19, 17 on the side of a TG, and a filter 23 which traps an unwanted frequency is installed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrum analyzer having a tracking generator (hereinafter referred to as TG) built-in, and the signal of the TG leaks to the receiving side, which makes it difficult to measure a weak receiving input signal. ,
The present invention relates to a circuit that prevents deterioration of the performance of a measuring instrument, that is, the performance of a measurement dynamic range due to an increase in measurement error.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing the configuration of an embodiment of a conventional spectrum analyzer. Further, FIG. 3 shows an example of a measurement mode in which a device under test (DUT) is connected. The main components are composed of a TG unit 20, a synthesizer 14, an isolation amplifier 22, an RF reception input unit, a mixer 12, and an IF unit 13.

First, the principle operation of the TG built-in spectrum analyzer will be described. The TG output signal 31 has an output level at the output unit 15 after the oscillation frequency f41 of the synthesizer 14 (including the variable voltage oscillator and the signal distribution circuit) and the frequency f42 of the fixed oscillator 17 are mixed by the mixer 16. After setting arbitrarily, TG frequency f43 =
(F41-f42) is output and supplied.

Here, the oscillation frequency of the synthesizer is swept (for example, f41 = 4.0001 GHz-).
7.6 GHz), an arbitrary TG output frequency (for example, f43 = 10 KHz to 3.6 GHz) can be obtained, and is used for measurement of an external DUT. Then, as shown in FIG. 3, the TG output signal 31 is supplied to the DUT 33, and the output signal from the DUT is input to the reception input 32. Then, it is input to one of the mixers 12 via the input attenuator 11 of FIG. On the other hand, the oscillation frequency f41 of the synthesizer is also supplied to the mixer 12. As a result, it is mixed with the received frequency, and the intermediate frequency f45 = (f41−f44)
After being converted to, the data is output to the IF unit 13.

Next, the relationship between the TG output frequency and the IF frequency will be explained, and its problems will be explained. IF section frequency f45
Requires that the frequency mixed by the reception input 32 and the frequency f41 (for example, 4.0001 GHz to 7.6 GHz) swept by the synthesizer 14 is always a constant IF frequency (for example, 4 GHz).

Therefore, on the TG output frequency side, a fixed oscillator 17 having the same oscillation frequency as the IF frequency is provided and mixed with the frequency f41 swept by the synthesizer 14 to obtain the TG output frequency. That is, the fixed oscillator 1
7 and the tuning frequency f4 of the IF unit 13.
5 must have the same frequency, that is, f45 = f42.

However, because of the above, there are the following problems. That is, since the fixed oscillator 17 has the same IF frequency, an extremely weak spurious signal leaking from the fixed oscillator 17 (hereinafter referred to as a residual response).
However, when entering the IF unit 13, it is measured as if it was a received input from the outside.

This adverse effect causes problems that the originally weak external input signal cannot be measured, the measurement error increases, and the measurement dynamic range decreases. Here, the dynamic range performance of the measuring device is mainly determined by the thermal noise (bandwidth and signal source impedance) level and the residual response from the TG. Including both, the dynamic range needs to be, for example, −130 dbm or less.

Due to the above-mentioned adverse effects, the following measures have been conventionally taken. The first is mechanical shield measures. That is, the fixed oscillator 17 and the mixer 16
Is distanced from the IF unit 13 or is surrounded by an aluminum shield block or the like to be completely shielded and cut off to prevent leakage. It is possible to take sufficient measures for this, but since there are restrictions on mounting space, layout, cost, etc., measures are taken to the extent that they do not interfere with actual use.

The second is a countermeasure against electrical reverse isolation. That is, the signal of the fixed oscillator 17 leaks to the IF unit 13 via the circuit in the reverse direction. This is because the signal of the fixed oscillator 17 passes through the mixer 16, the isolation amplifier, the synthesizer 14, and the mixer 12, as shown by the path of the TG leakage path 30 in FIG. This is a problem that leaks to the IF unit 13.

Moreover, in the conventional structure, it is not possible to insert a trap circuit in this path 30 to take measures against isolation. The reason is that, for example, if the sweep frequency of the synthesizer is f41 = 4.001 GHz to 7.6 GHz, the fixed oscillator on the TG side and the IF tuning frequency are 4 GHz.
Hz. At this time, the trap frequency for preventing leakage from the TG is 4 GHz. However, since it is almost the same as the lower limit frequency of 4.0001 GHz of the sweep frequency of the synthesizer, there is only 0.0001 GHz difference, and if the trap circuit is inserted, the signal of the synthesizer 14 is also trapped and cannot be used. .

For this reason, isolation measures are taken by another method. That is, the isolation amplifier 22 is provided between the mixer 16 and the synthesizer 14, and the reverse transfer characteristic (isolation characteristic) by this is used to prevent TG leakage.

The isolation amplifier 22 is inserted as a measure for reducing the transmission in the reverse direction, and a plurality of isolation amplifiers are used to obtain a required isolation characteristic. Also, the isolation characteristic of the amplifier used here has a high frequency of 4 GHz or more, and therefore the isolation performance of the amplifier itself and the attenuation amount obtained by inserting the attenuator amplified by the amplifier are added. Also, 20 to 30 per step
You can only get about db. Therefore, in order to obtain the required amount of isolation, the isolation amplifier is configured by connecting 3 to 4 stages in series.

Moreover, the isolation amplifier used here is expensive because it requires a dedicated high-frequency amplifier having good isolation characteristics as described above, which is a factor of cost increase. Further, in order to make the shield structure of the circuit strict, a lot of mounting space including peripheral circuits is required.

Even if the above-mentioned measures are taken, weak external input signals cannot be measured due to variations in assembly and mounting, or leakage from the isolation amplifier, and measurement is performed for each product. This is a cause of variations in the dynamic range performance of the vessel. For this reason, in applications where a weak signal level such as a noise level is measured, or in order to measure a wide dynamic range, the isolation amplifier is added further,
It is necessary to improve the mounting shield improvement method.

[0016]

As described above, since the oscillation frequency of the fixed oscillator 17 is the same as the intermediate frequency f45 of the IF section, the TG leakage path 30 shown in FIG.
This is a problem of leaking to the IF unit 13 as shown by the route of.

For this reason, conventionally, a plurality of isolation amplifiers have been inserted between the synthesizer 14 and the mixer 16 so as to have the required isolation characteristics. This isolation characteristic is one of the factors that determine performance. To improve the measurement performance,
It is necessary to add more isolation amplifiers, increasing product costs and increasing circuit installation space. Moreover, even more shielding measures will be needed.

Therefore, the problem to be solved by the present invention is to eliminate the isolation problem itself on the IF side and the TG side in principle. That is, the circuit is configured so that the TG side does not have the same oscillation source as the intermediate frequency of the IF section. This aims to improve the dynamic range of the measurement. Moreover, the purpose of the present invention is not to use an expensive isolation amplifier as in the prior art, but also to reduce strict shield measures to achieve cost reduction at the same time.

[0019]

In order to solve the above problems, the structure of the present invention is provided with a synthesizer 14, fixed oscillators 19 and 17, mixers 18, 16 and 12, and a filter 23. . This configuration eliminates the problem that the conventional device has, that is, the problem that it has the same oscillation source as the IF frequency, and eliminates the source of the residual response itself.

That is, the solution according to the present invention is the IF
Two oscillation frequencies f different from the tuning frequency f6 of the section 13
2 and f4 are provided, and the synthesizer 14 and these two are sequentially mixed to provide the TG output frequency.

A synthesizer 14 for sweeping the frequency is provided and is supplied to the mixer 18 and the mixer 12. Next, the mixer 18 mixes the output signals of the synthesizer and the fixed oscillator 19. Next, the output signal of the mixer 18 is supplied to the filter 23. next,
After the unnecessary frequency component is deleted by the filter 23, it is supplied to the mixer 16. Next, the output signal of the filter 23 and the output signal of the fixed oscillator 17 are mixed by the mixer 16. Next, the output signal of the mixer 16 is output to the output unit 1
After being attenuated to the output level in 5, the TG signal is output to the outside. Then, the received input signal and the synthesizer are mixed by the mixer 12, and then supplied to the IF unit 13.

As the connecting means, the output of the synthesizer 14 is supplied to one input of the mixer 18 and one of the mixers 12, and the output of the fixed oscillator 19 is supplied to the mixer 1.
8 and the output of the mixer 18 to the input of the filter 23, the output of the filter 23 to one input of the mixer 16, the output of the fixed oscillator 17 to the other input of the mixer 16. And the output of the mixer 16 is supplied to the output unit 15. Further, the received input signal is supplied to the input attenuator 11, the output of the input attenuator is supplied to the other of the mixers 12, and the output of the mixer 12 is supplied to the IF unit 13. A spectrum analyzer with a built-in tracking generator, comprising the above.

There is a configuration in which the following means is added between the filter 23 and the mixer 16 in the above-mentioned configuration means to further remove the residual response. An amplifier 21 that amplifies the output signal of the filter 23 is provided. Then, a filter 24 for filtering the output signal of the amplifier 21 is provided. As a result, the input signal of the filter 23 is amplified by the amplifier and supplied to the filter 24. The filter 24 further removes unnecessary frequency components that could not be completely removed by the filter of the filter 23, and then supplies them to the mixer 16.

As the connecting means, the output of the filter 23 is supplied to the input of the amplifier 21 with respect to the above connection configuration,
The output of the amplifier is supplied to the input of the filter 24, and the output of the filter 24 is supplied to one of the mixers 16. A spectrum analyzer with a built-in tracking generator, comprising the above.

[0025]

Operation: Oscillation frequencies f2 and f4 of the fixed oscillators 17 and 19
Since the frequency is different from the intermediate frequency f6 of the IF section, even if there is a leak from the fixed oscillator to the IF section, the frequency is different, so there is no influence.

In the conventional case, the trap circuit could not be inserted, but as a result of shifting the frequency up by the mixer 18, the trap circuit can be inserted between the output point of the mixer 18 and the input point of the mixer 16. . This trap has the following effects.

First, the filters 23 and 24 are provided with traps for the f2 frequency component. As a result, the mixer 16 has a function of preventing the generation of the (f4-f2) = f6 frequency component itself due to unintended mixing. Second, f
Filters 23 and 24 are provided with traps of 6 frequency components. As a result, the weak IF frequency component f6 generated by mixing in the mixer 16 has a function of preventing transmission in the opposite direction.

In the spectrum analyzer configured as described above, the oscillation source matching the IF frequency is almost completely eliminated. As a result, there is a residual response problem due to spurious as in the conventional case, a weak received signal can be measured, and the dynamic range performance of measurement can be improved.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the configuration block diagram of one embodiment of the spectrum analyzer of the present invention shown in FIG. Conventionally, the intermediate frequency f of the IF unit 13
By making 6 and the oscillation frequency f4 of the fixed oscillator 17 the same, the circuit has a simple circuit configuration. However, in recent years, there has been a demand for further improvement in measurement performance, and the isolation measures and the shield measures in the conventional circuit system have become more costly and mounting space increased, which is not a good idea.

Therefore, the solution according to the present invention uses two oscillation frequencies f different from the tuning frequency f6 of the IF section 13.
2 and f4 are provided, and the synthesizer 14 and these two oscillation frequencies are sequentially mixed to obtain the TG output frequency. Due to this, the part that changed from the past is
A fixed oscillator 19 is added, a mixer 18 is added, an amplifier 21 is added, filters 23 and 24 are added, and an isolation amplifier 22 is deleted.

This structure has the following problems.
In principle, the method has been changed to a circuit configuration that eliminates the source of spurious emission. That is, in the present invention, a fixed oscillator 19 and a mixer 18 are newly provided,
The oscillation source itself, which is an intermediate frequency of the IF frequency f6, is eliminated.

The flow of signals will be described. First, the sweep frequency signal output from the synthesizer 14 and the output frequency signal of the fixed oscillator 19 are mixed by the mixer 18, and then the output signal is supplied to the filter 23. To do. Here, the output frequency component from the mixer 18 is (f
1 + f2), (f2-f1), f2, and f1 are mixed, so a high-pass filter for passing only (f1 + f2) of the target frequency is used as the filter 2
Provide in 3.

When the f2 frequency component is supplied to the mixer 16 at the next stage, it is mixed with f4 to obtain (f4-f2).
Frequency components are generated. This is a frequency component that is weak but matches the IF frequency f6. Therefore, in order to prevent this from occurring, the filter 23 is provided with a trap circuit of f2 frequency so that it is not supplied to the mixer 16.

Here, in the conventional case, the trap circuit could not be inserted, but the mixer 18 shifts the frequency UP.
Therefore, the trap circuit can be easily inserted.

Still, since the weak IF frequency f6 is generated, the filter 23 is provided with a trap circuit of f6 frequency to surely eliminate spurious. here,
The trap circuit can easily obtain an attenuation amount of 40 dB or more by combining parallel resonance and series resonance, for example. Further, if a plurality of stages of this trap circuit are provided, it is possible to easily realize the required attenuation amount.

Next, the output signal of the filter 23 is supplied to the amplifier 21. The amplifier here amplifies and buffers the input signal level, and then outputs it to the filter 24 at the next stage. The amplifier used here may be a general high-frequency buffer amplifier. In other words, there is no need for an expensive multi-stage dedicated amplifier with good isolation characteristics as in the conventional case. Moreover, it is no longer necessary to take strict shield measures as in the past.

Like the filter 23, the filter 24 is composed of a high-pass filter and a trap circuit, and attenuates unnecessary frequency components and outputs them to the mixer 16 as described above. If the filter 23 is configured to obtain a sufficient amount of attenuation, the filter 24 may be deleted. Also, if signal level amplification is not needed,
The amplifier 21 may be deleted.

Next, the output frequency (f
1 + f2) and the output frequency f4 of the fixed oscillator 17 are mixed by the mixer 16, and the output frequency (f1 + f2-
f4) is supplied to the output unit 15. Then, the output section 15 makes a desired output level through a low-pass filter, a buffer amplifier and an attenuator, and then outputs a TG output 31 for external supply.

[0039]

Since the present invention is configured as described above, it has the following effects. I
Since there is no oscillation source that matches the F frequency f6, the residual response due to spurious as in the past disappears,
The weak received signal can be measured, and the dynamic range performance of the measurement is improved.

For the above reason, it is no longer necessary to insert an isolation amplifier as in the conventional case. That is,
The amplifier 21 used here may be a general inexpensive high-frequency buffer amplifier. It is no longer necessary to use a multi-stage amplifier, which is expensive and has good isolation characteristics as in the past.

In the conventional case, the trap circuit could not be inserted, but since the frequency was shifted up by the mixer 18, the trap circuit could be easily inserted. This trap causes a weak I generated secondly in the mixer 16.
It can be easily realized that almost all F frequency components are deleted. Further, since the fixed oscillator in the TG section is no longer at the IF frequency f6 as in the conventional case, the fixed oscillators 17 and 19 are
No longer requires strict shielding measures.

[0042]

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment of a spectrum analyzer of the present invention.

FIG. 2 is a configuration block diagram of an embodiment of a conventional spectrum analyzer.

FIG. 3 is a diagram showing an example of a measurement mode in which a device under test (DUT) is connected.

[Explanation of symbols]

 11 Input Attenuator Section 12, 16, 18 Mixer 13 IF Section 14 Synthesizer 15 Output Section 17, 19 Fixed Oscillator 20 TG Section 21 Amplifier 22 Isolation Amplifier 23, 24 Filter

Claims (2)

[Claims] 1. A spectrum analyzer incorporating a tracking generator, comprising a synthesizer (14) for sweeping a frequency, and a fixed oscillator (19) for mixing with the synthesizer.
The output signal of the synthesizer and the fixed oscillator (19)
A fixed oscillator (17) having a mixer (18) for mixing the output signal of the filter, a filter (23) for filtering the output signal of the mixer (18), and mixing with the output signal of the filter (23) And an output signal of the filter (23) and a fixed oscillator (17)
And a mixer (12) for mixing the received input signal and the synthesizer, and a mixer (12) for mixing the received input signal and the synthesizer. analyzer. 2. The filter (23) according to claim 1, wherein
And the mixer (16) between the amplifier (2) for amplifying the output signal of the filter (23).
The spectrum analyzer with a built-in tracking generator according to claim 1, further comprising: a filter (24) for filtering an output signal of the amplifier (21).