JPH08201450A - Spectrum analyzer - Google Patents

Abstract

PURPOSE: To provide a further inexpensive oscillation source by performing the linear correction such that the voltage controlled oscillation frequency of a variable capacity diode generates a sweeping frequency of constant inclination. CONSTITUTION: The constitution of a sweep control section 70 is additionally provided with a linear correction section 78 thus providing an additional code data conversion processing for correcting the linearity of a varactor tuned voltage controlled oscillator(VCO) 20. The correcting section 78 is provided with a linearity correction table 79 prestored with correction values 79dal for determining the characteristic curve of control voltage 38uosc vs oscillation frequency. The correction value 79dal is read out using a code data 72cod , received from a ramp signal generating section 72, as an address. It is then multiplied by the data 72cod to produce a conversion code data 78cod subjected to linearity correction which is then fed to a DA converter 74. Consequently, the VCO 20 can oscillates a linear sweeping frequency having incremental inclination of a constant frequency. Since a local oscillator 30 can be constituted of a relatively inexpensive VCO circuit, a further inexpensive oscillation source can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrum analyzer for inexpensively constructing an oscillation source used for a local oscillator.

[0002]

2. Description of the Related Art Conventionally, as an oscillation source used for a local oscillator of a spectrum analyzer, YIG (Yttr
There is an example of a spectrum analyzer using (ium Iron Garnet). This will be described with reference to FIGS. 4, 5, and 6. This device, as shown in the block diagram of FIG.
Frequency converter 50, sweep controller 70, detector 62
And a display calculation section 64 and a display section 68.

The frequency conversion section 50 has the principle configuration of a frequency conversion section of a general spectrum analyzer. The frequency conversion section 50 receives a signal under test 100, sweeps a desired frequency range with a local oscillator, and converts it into a constant intermediate frequency. , BPF (bandpass filter) after filtering to the desired bandwidth characteristics,
It is supplied to the detection unit 62. The detection unit 62 detects the signal obtained by the sweeping, converts the signal into a digital signal, and supplies the digital signal to the display calculation unit 64. In this frequency conversion unit 50,
There is a local oscillator 30 that receives and sweeps a sweep ramp signal 76sweep.

The sweep control unit 70 supplies a swept analog ramp waveform to the local oscillator 30, and upon receipt of the sweep start signal 70stt, the ramp generation unit 72 responds to a span frequency (sweep range frequency) section. Then, the code data for sweeping the ramp at a constant slope is sequentially supplied to the DA converter 74 at a time interval corresponding to the sweep speed, converted into an analog staircase waveform, and filtered by a LPF (low-pass filter) 76 into a linear slope. The ramp signal 76sweep is supplied to the local oscillator 30.

The local oscillator 30 outputs a ramp signal 76sweep.
In response to this, an oscillator for sweeping a sweep frequency range,
As shown in FIG. 5, the internal configuration is such that the frequency dividers 34 and 37 are
, A phase comparator 36, an integrator 35, an adder 38,
It is composed of a YTO (YIG-tuned Oscillator) 40.

The YTO 40 has a PLL before the sweep.
A locked loop of (Phase Locked Loop) is formed to oscillate the center frequency f0 which is the intermediate value of the sweep frequency, and the phase is locked. Lamp signal 76 at this time
The sweep voltage is in the 0v state. Next, when the sweep is started, the analog potential 35vosc at the output end of the integrator 35 is controlled to be switched to the holding state. As a result, the PLL lock loop is released and a free-run state in which the PLL lock loop oscillates at the center frequency f0 is established. In this state, the ramp signal 76sweep from the sweep control unit 70 is supplied to one end of the analog adder 38 to add the analog potential 35vosc to the control voltage 38vosc.
Is supplied to the YTO 40 to generate an oscillation frequency for sweeping the lamp. That is, at the time of sweeping, a free-run state is set and an analog voltage obtained by adding the ramp signal 76sweep is applied to the voltage-controlled oscillation input end to sweep. Therefore, YTO40
Therefore, an oscillation source with good linearity that generates an oscillation frequency proportional to the input analog voltage is required.

The internal circuit configuration of the YTO 40, which is a VCO (voltage controlled oscillator), will be described with reference to FIG. The YTO 40 is a VCO using the YIG resonator 42.
In addition, the oscillator having excellent linearity, in which the value of the current flowing through the coil 42b and the value of the oscillation frequency are in a proportional relationship. The control voltage 38vosc signal from the adder 38 is received, converted into a current by the IV converter 41, and then supplied to the coil 42b, and then Y
A magnetic field is applied to the IG resonator 42. By this, YIG
The resonator 42 has a tuning frequency proportional to the magnetic field. Using this as a resonance circuit, the transistor 43, the series feedback element 44, and the output matching network (MN)
An oscillation circuit is formed by the negative resistance circuit 49 configured by. The negative resistance circuit 49 gives parameters of each element so that the negative resistance satisfies the oscillation condition in the oscillation frequency range used, for example, in the range of 4 to 8 GHz. An oscillation frequency signal 40osc obtained by buffer-amplifying the oscillation signal from this oscillation circuit with a buffer amplifier 48 is output. This YIG
By using a resonator, a sweep frequency with good linearity accuracy can be generated during sweep, and high frequency accuracy of spectrum measurement is maintained.

[0008]

As described above, the local oscillator 30 is swept by the analog voltage obtained by adding the ramp signal 76sweep to the voltage-controlled oscillation input terminal in the free-run state at the time of sweeping. In the analyzer, a VCO using a YIG element having good linearity that generates an oscillation frequency proportional to the input analog voltage is used as the VCO. However, this YIG element is relatively expensive and has a drawback that it accounts for a relatively large proportion of the product cost.

Therefore, the problem to be solved by the present invention is to reduce the cost by using a relatively inexpensive VCO circuit instead of the YIG resonator and constructing a local oscillator that corrects this linearity. The purpose is to realize an oscillating source for various spectrum analyzers.

[0010]

In order to solve the above-mentioned problems, in the structure of the present invention, a straight line for correcting the voltage controlled oscillation frequency of the variable capacitance diode 24 so as to generate a sweep frequency having a constant slope. The property correction section 78 is provided as a constituent means. As a result, for a relatively inexpensive spectrum analyzer that has the local oscillator 30 that configures the voltage controlled oscillator VCO using the variable capacitance diode 24 for microwaves and sweeps with good linearity by receiving the analog sweep ramp signal 76sweep. The local oscillator 30 is realized.

As a concrete means, by receiving the code data 72cod from the ramp generating section 72 of the sweep control section 70,
Linearity correction that outputs conversion code data 78cod that has undergone linearity correction processing in which the oscillation frequency of the voltage controlled oscillator has an increasing slope of a constant frequency that is proportional to the ramp sweep, and corrects the sweep frequency by the analog sweep ramp signal 76sweep. There is a constituent means for providing the means 78.

[0012]

The linearity correction section 78 receives the code data 72cod from the ramp generation section 72 and receives the varactor tune V
The conversion code data 78cod is linearly corrected so that the oscillation frequency of the CO 20 has an increasing slope of a constant frequency proportional to the lamp sweep. A local oscillator 30 that configures a VCO using the variable capacitance diode for microwaves 24 as a variable tuning element, converts it into code data for correcting the sweep linearity of the oscillation frequency by the linearity correction unit 78 of the sweep control unit 70, and performs ramp sweep is used. , It is possible to obtain the effect of maintaining the frequency accuracy of spectrum measurement at the same level as the conventional one.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present invention is an example in which the local oscillator is composed of a varactor tuned VCO. This will be described with reference to FIGS. 1 and 2. The configuration of the entire apparatus is the same as the conventional configuration shown in FIG. 4, but in this, the local oscillator 30 of the frequency conversion unit 50 and the sweep control unit 7 are included.
The composition of 0 is changed. In the local oscillator 30, as shown in FIG. 1, instead of the YTO 40, a varactor tuned V
The configuration is such that CO20 is replaced. Further, the sweep control unit 70 has a configuration in which a linearity correction unit 78 is additionally provided in front of the DA converter 74.

As shown in FIG. 2, the internal structure of the varactor tuned VCO 20 is composed of a variable tuning circuit 21, a negative resistance circuit 49, and a buffer amplifier 48. The negative resistance circuit 49 and the buffer amplifier 48 are provided. 48 is the same as the conventional one. The variable tuning circuit 21 is a tank circuit (Tank Circuit) using a microwave variable capacitance diode 24 as a variable tuning element, and includes a lumped constant equivalent resonance coil 29 and an equivalent resonance capacitance 28. Are in the microwave band, so they are formed by the distributed constants of the microstrip line. The variable capacitance diode 24 is
For example, it is a tuning diode element (GaAs Tuning Diode chip) using gallium arsenide (GaAs).
An element applicable to the z band is used. The variable capacitance diode 24 is connected in series with the tank circuit and the capacitor 26 to form a resonance circuit as a whole. The control voltage 38vosc, which is a DC voltage, is applied to the variable capacitance diode 24 through the high resistance 22.

Here, the characteristic of the oscillation frequency with respect to the control voltage 38vosc given to the variable capacitance diode 24 is shown in an example of the voltage sensitivity characteristic curve of the oscillation frequency of FIG. The variable-capacitance diode has a different non-linear curve for each sample A and sample B. Therefore, the control voltage 38vosc from the sweep control unit 70 is supplied with the control voltage 38vosc obtained by correcting and converting the non-linear curve for linearity correction.

The internal structure of the sweep control unit 70 is, as shown in FIG. 1, a ramp generation unit 72, a linearity correction unit 78, and a D
The varactor tuned VCO 20 includes an A converter 74 and an LPF 76, and a linearity correction unit 78 is added.
A code data conversion process to correct the linearity of is added. The internal linearity correction table 79 has a control voltage 38
The correction value 79dat for which the oscillation frequency characteristic curve for vosc has been obtained is stored in advance. Upon receiving the code data 72cod from the ramp generator 72, the correction value 79dat of the linearity correction table 79 having this as an address is read, and the conversion code data 78cod corrected by linearity by multiplication with the code data 72cod is DA converted. Supply to the container 74.
As a result, the varactor tuned VCO 20 can oscillate and output a sweep frequency having a linearity with a constant frequency increasing slope. By the way, providing a correction value for all the code data from the ramp generating section 72 in the linearity correction table 79 requires a large memory capacity. Therefore, it is sufficient for the linearity correction to be within ± 0.1%. Therefore, the correction value for the code data 72cod for each desired interval is stored, and the code data in this section is calculated by the linear interpolation method and the correction calculation is performed. .

In the above description of the embodiment, the correction value 79dat is stored in the linearity correction table 79 in advance. However, in the case where the frequency counter for measuring the oscillation frequency of the local oscillator 30 is built-in, the correction value 79dat is stored in advance. It is also possible to oscillate with each code data 72cod in the current environment, measure the oscillation frequency at any time as desired, calculate a correction value 79dat from this, store it in the linearity correction table 79, and then execute sweeping. Can be carried out.

[0018]

Since the present invention is configured as described above, it has the following effects. The linearity correction unit 78 of the sweep control unit 70 has the effect of correcting the nonlinearity of the oscillation frequency of the varactor tuned VCO 20 to enable the linearity-corrected sweep so that the sweep frequency has an increasing slope of a constant frequency. can get. A local oscillator 30 that configures a VCO using the variable capacitance diode for microwaves 24 as a variable tuning element, converts it into code data for correcting the sweep linearity of the oscillation frequency by the linearity correction unit 78 of the sweep control unit 70, and performs ramp sweep is used. , It is possible to obtain the effect of maintaining the frequency accuracy of spectrum measurement at the same level as the conventional one.
From these, it is possible to obtain the effect of realizing an oscillation source of a spectrum analyzer which is cheaper than the conventional one.

[0019]

[Brief description of drawings]

FIG. 1 is a configuration diagram of a local oscillator 30 and a sweep control unit 70 of the present invention.

FIG. 2 is a block diagram of a varactor tuned VCO 20 of the present invention.

FIG. 3 is an example of a voltage sensitivity characteristic curve of an oscillation frequency of a variable capacitance diode 24.

FIG. 4 is an overall configuration diagram of a conventional local oscillator 30.

FIG. 5 is a configuration diagram of a conventional YTO 40.

[Figure 6]

[Explanation of symbols]

 20 varactor tuned VCO 21 variable tuning circuit 24 variable capacitance diode 26 capacitor 28 equivalent resonance capacitance 29 equivalent resonance coil 30 local oscillator 34, 37 frequency divider 35 integrator 35 vosc analog potential 36 phase comparator 38 adder 38 vosc control voltage 40 YTO (YIG-tuned Oscillator) 40osc Oscillation frequency signal 41 IV converter 42 YIG resonator 42b Coil 43 Transistor 44 Series feedback element 48 Buffer amplifier 49 Negative resistance circuit 50 Frequency conversion unit 62 Detection unit 64 Display operation unit 68 Display unit 70 Sweep control unit 70stt Sweep start signal 72 Ramp generation unit 72cod code data 74 DA converter 76 sweep ramp signal 76 LPF (low pass filter) 78 Linearity correction unit 78cod conversion code data 79 Linearity correction table 00 signal to be measured

Claims (2)

[Claims] 1. A variable capacitance diode for microwaves (2
4) using a local oscillator (30) which constitutes a voltage controlled oscillator (VCO), and which receives and sweeps an analog sweep ramp signal (76sweep), the variable capacitance diode (30) A spectrum analyzer characterized in that a linearity correction section (78) means for correcting the voltage-controlled oscillation frequency of 24) to generate a sweep frequency having a constant slope is provided. 2. A variable capacitance diode for microwaves (2
In the local oscillator (30) which has a local oscillator (30) which constitutes a voltage controlled oscillator (VCO) using 4) and which receives and sweeps an analog sweep ramp signal (76sweep), a sweep control unit (70) ) Received the code data (72cod) from the ramp generator (72), the conversion frequency of the voltage-controlled oscillator is converted into linearity correction processing that has an increasing slope of a constant frequency proportional to the ramp sweep (78cod).
d) is output to output an analog sweep ramp signal (76sweep)
Linearity correction unit (7
8) A spectrum analyzer provided with means and having the above.