JPH0227616Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a reference frequency signal generator commonly called SG, etc., and specifically aims to provide a signal generator that prevents the output signal level from fluctuating as the frequency changes. It is.

<Prior Art> Figure 1 shows the configuration of a conventional signal generator. In the figure, 1 indicates a signal source. This signal source 1 outputs a signal whose frequency is accurately calibrated. 2 is a gain adjustment circuit, 3 is an output amplifier, 4 is a variable attenuator, and 5 is an output terminal.

Conventionally, in such a signal generator, an automatic level control circuit 6 is provided to prevent level fluctuations of the output signal. This automatic level control circuit 6 takes out a signal from the input side of the variable attenuator 4,
The extracted signal is detected by the detector 7, and the detected output of the detector 7 is compared with the voltage of the level setting reference voltage source 8 by the voltage comparator 9.
The gain of the gain adjustment circuit 2 is adjusted based on the comparison output, and the level of the signal applied to the variable attenuator 4 is automatically controlled to a constant value.

With this configuration, the level of the signal output from the output terminal 5 is maintained at a constant level defined by the amount of attenuation set by the variable attenuator 4.

<Conventional disadvantages> By the way, the signal source 1 can change the oscillation frequency over a fairly wide range. For example, even if the gain adjustment circuit 2 and the output amplifier 3 have frequency characteristics, the signal level on the input side of the variable attenuator 4 is maintained at a nearly constant value by the automatic level control circuit 6 described above, regardless of frequency changes. be done.

On the other hand, recently, relays and the like have been used so that the amount of attenuation of the variable attenuator 4 can be automatically switched by a control signal. Therefore, since the relay contacts are inserted into the signal path, the relay contacts have frequency characteristics with respect to high-frequency signals, and because of this, the variable attenuator 4 tends to have frequency characteristics as shown in FIG. 5A, for example. There is.

If the variable attenuator 4 has frequency characteristics, level fluctuations due to the frequency characteristics appear at the output terminal. In order to eliminate level fluctuations due to the frequency characteristics of the variable attenuator 4, the signal output point of the automatic level control circuit 6 may be selected as the output terminal 5. However, with this configuration, even if the amount of attenuation in the variable attenuator 4 is changed, the output level of the output terminal 5 will be held at a constant value by the action of the control loop, and the variable attenuator 4 will not function at all. It becomes impossible to set the level of the signal output to the desired level.

Therefore, as a method of eliminating the influence of the frequency characteristics of the variable attenuator 4, a configuration as shown in FIG. 2 has been considered.

In FIG. 2, 11 indicates a microcomputer. The frequency of the signal output to the output terminal 5 is taken into the microcomputer 11. Correction data obtained by measuring the frequency characteristics of the variable attenuator 4 was stored in advance in the microcomputer 11.
It has a built-in ROM 11a, reads a correction value for the frequency from an address corresponding to the frequency of the output signal, converts the correction data from D to A by a D-A converter 11b, and supplies it to the reference voltage source 8, for example. There is a device that corrects the reference voltage output from 8 to correct level fluctuations in the output voltage.

With such a correction device, level fluctuations in the output signal caused by the frequency characteristics of the variable attenuator 4 can be corrected.

However, since the storage capacity of the ROM 11a is limited, it is not possible to store correction values for all continuously changing frequencies. For this reason, or because the corrected values are stored at frequency intervals, the level of the corrected output signal has the drawback of fluctuating in a sawtooth pattern as shown in FIG. 3 when viewed microscopically. Furthermore, when the frequency is changed, the microcomputer 11 takes in the change in frequency and generates an address signal corresponding to that frequency, and it takes some time to read out the ROM 11a, and the level of the output signal is corrected. The disadvantage is that there is a time delay. Furthermore, the frequency of the variable attenuator 4 must be measured for each product, corrected data must be obtained from the measurement results, and the corrected data must be written into the ROM 11a, which makes manufacturing complicated. Additionally, since a microcomputer must be used, the overall cost is high.

<Purpose of the invention> The purpose of this invention is to provide a signal generator that does not use a microcomputer, can be continuously corrected, and can be manufactured at low cost.

<Summary of the invention> In this invention, a pseudo loss circuit with frequency characteristics equivalent to that of a variable attenuator is inserted into the automatic level control circuit, and the correction characteristics of the automatic level control circuit have frequency characteristics due to the frequency characteristics of this pseudo loss circuit. height,
This correction characteristic is configured to correct level errors caused by the frequency characteristics of the variable attenuator.

<Example of the invention> Fig. 4 shows an example of the invention. 1st in the diagram
Parts corresponding to those in the figure are designated by the same reference numerals.

In this invention, a signal taken out from the input side of the variable attenuator 4 is supplied to a pseudo loss circuit 12 having frequency characteristics equivalent to the frequency characteristics of the variable attenuator 4,
The signal extracted through the pseudo loss circuit 12 is detected by the detector 7, and the detected output is sent to the voltage comparator 9.
It is configured to supply

The signal may be branched by any method, but in this example, the directional coupler 13 is provided before the variable attenuator 4, and the branch output terminal 1 of the directional coupler 13 is connected to the branch output terminal 1 of the directional coupler 13.
A case is shown in which the signal is taken out from 3a. By using the directional coupler 13 in this way, the reverse signal coming from the output terminal does not appear at the branch output terminal 13a due to this directional effect. Therefore, since the backward signal does not mix into the automatic level control circuit 6, intermodulation distortion caused by the backward signal and the output signal can be reduced. This often occurs when two, three, or multiple signals are combined using a power combiner, and deteriorates the measurement dynamic range when testing intermodulation distortion of nonlinear elements. This problem can be alleviated by configuring as in one embodiment of the present application.

<Operation and Effect of the Invention> According to the above-mentioned configuration of the present application, the frequency characteristics of the variable attenuator 4 are such that, as shown in FIG. 5A, for example, the attenuation amount gradually increases on the high frequency side as the frequency increases If it is hot, pseudo loss circuit 1
The frequency characteristics of No. 2 are also selected to be similar to this.

If the frequency characteristics of the pseudo loss circuit 12 are as shown in FIG. 5A, the voltage of the detected output signal of the detector 7 will be a voltage signal that gradually decreases as the frequency increases, as shown in FIG. 5B. It will be done. By applying this detection output signal to, for example, the inverting input terminal (-) of the voltage comparator 9, a DC signal that increases toward the positive voltage side as the frequency increases is obtained from the voltage comparator 9, as shown in FIG. 5C. . By supplying this DC signal to the gain adjustment circuit 2, the gain of the gain adjustment circuit 2 is controlled, and if the gain of the gain adjustment circuit 2 is controlled to gradually increase as the frequency increases, the frequency characteristics of the variable attenuator 4 can be controlled. Level fluctuations are corrected, and a signal having a uniform level at any frequency can be output to the output terminal 5.

Therefore, according to this invention, the level of the signal obtained at the output terminal 5 is continuously modified, and it is possible to obtain a signal with a uniform level over the low frequency range from the low frequency range to the high frequency range. Furthermore, the time required for level correction is almost zero, and there is no time delay in level correction.

Further, when the directional coupler 13 is used as a means for branching signals for level correction, as described above, it is not possible to extract the reverse direction signal input from the outside to the output terminal 13a due to its directionality.
Therefore, since the backward signal does not mix into the automatic level control circuit 6, intermodulation distortion caused by the backward signal and the output signal can be reduced.

Further, the pseudo loss circuit 12 can be easily created if the frequency characteristics of the variable attenuator 4 are roughly understood. Therefore, manufacturing is easier compared to the method of writing correction data to the ROM 11a as shown in FIG.

[Brief explanation of the drawing]

1 and 2 are block diagrams for explaining a conventional signal generator, FIG. 3 is a graph for explaining the operation of FIG. 2, and FIG. 4 is a block diagram showing an embodiment of this invention. 5 are graphs for explaining the operation of this invention. 1: Signal source, 2: Gain adjustment circuit, 3: Output amplifier, 4: Variable attenuator, 5: Output terminal, 6: Automatic level control circuit, 7: Detector, 8: Reference voltage source,
9: Voltage comparator, 12: Pseudo loss circuit, 13: Directional coupler.

Claims (1)

[Scope of utility model registration request] In a signal generator in which a variable attenuator is connected to the output stage and a signal is output through this variable attenuator, a signal is output from the stage before the variable attenuator through a pseudo loss circuit having frequency characteristics equivalent to that of the variable attenuator. A signal generator configured to extract the above signal, compare the extracted signal with a reference voltage, and use the comparison output to control the gain adjustment means provided at the front stage of the variable attenuator to obtain a signal without frequency characteristics. vessel.