JPH0720607Y2 - Signal source for level calibration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Industrial field of application” The present invention relates to a signal source for level calibration, which is used by being incorporated in various measuring instruments, for example.

“Prior Art” FIG. 2 shows a conventional level calibration signal source.

The conventional level calibrating signal source includes a reference signal source 10 and a high-precision attenuator 20 that variably attenuates the signal output from the reference signal source 10 in fixed steps.

As the reference signal source 10, an oscillator with high stability is used. The high-precision attenuator 20 has an attenuator 21 that gives 1 dB of attenuation and an attenuator 22 that gives 2 dB of attenuation.
It is composed of two attenuators 23, 24 that give dB attenuation and switches SW ₁ , SW ₂ , SW _3, ... SW ₈ that continuously connect these attenuators 21, 22, 23, 24 in any combination. It

By switching these switches SW _{1 to} SW ₈ appropriately,
A calibration signal that changes in steps of 1 dB and changes from 0 to -10 dB can be obtained at the output terminal 30, and this signal is used to adjust the sensitivity of the measuring instrument, for example.

[Problems to be Solved by the Invention] According to the configuration of the conventional level calibration signal source, the stability of the calibration signal obtained at the output terminal 30 depends on the stability of the reference signal source 10.

Therefore, the stability of the calibration signal source must be controlled with high accuracy.

Further, since the switches SW _{1 to} SW ₈ generally use relays, eight relays, a switching control circuit for switching and controlling the relays so that the attenuation amount changes in 1 dB steps, and an attenuator
Four high-precision resistors constituting 21,22,23,24 are required, and these parts are expensive, so that there is a drawback that the cost becomes high.

"Means for Solving the Problem" In the present invention, a calibration reference signal is applied from a reference signal source to a differential type saturation amplifier whose operating current is limited by a current source circuit, and its amplified output is taken out as a calibration signal. Along with this, the current value of the current source circuit is configured to be controlled by the output of the DA converter.

[Operation] According to the configuration of the present invention, the gain of the differential saturation amplifier is determined only by the current flowing through the current source circuit.

However, since the differential amplifier operates as a saturation amplifier, the amplitude value of the output signal is determined by the product of the operating current and the resistance value of the load resistor.

Therefore, the current value of the current source circuit is uniquely determined by giving the desired level set value to the DA converter, so that it is output from the differential amplifier by changing the digital data given to the DA converter in predetermined steps. The signal level can be changed accurately.

Since the differential amplifier operates as a saturation amplifier, even if the level of the reference signal supplied from the reference signal source fluctuates, the fluctuation does not appear on the output side unless the operating current value i changes.

Therefore, it is possible to provide a calibration signal source having high stability and high accuracy of change steps.

"Embodiment" FIG. 1 shows an embodiment of the present invention. In the figure, 10 is a reference signal source, 40 is a differential saturation amplifier, and 50 is this differential saturation amplifier.
A current source circuit that regulates the operating current of 40, and 60 is a DA converter.

In this embodiment, the low-pass filter 70 is provided on the output side of the differential saturation amplifier 40, and the rectangular wave-shaped reference signal output from the differential saturation amplifier 40 is converted into a sine wave and output to the output terminal 30. The configuration is shown as follows.

The differential saturation amplifier 40 can be composed of a pair of transistors 41 and 42 and load resistors 43 and 44 connected to the collectors of the transistors 41 and 42, and a reference signal source is provided at the base of one transistor 41. Give the reference signal from 10. The base of the other transistor 44 is grounded, and the output signal is taken out from the collector of this transistor 44.

As the current source circuit 50, a known constant current source circuit can be used. An analog signal obtained by DA conversion from the DA converter 60 is applied to the current control terminal of the current source circuit 50,
Control the current i flowing through 50.

When a sine wave is applied from the reference signal source 10 in the above configuration, the differential amplifier 40 saturates and amplifies this sine wave, and the output becomes a rectangular wave. A sine wave can be output to the output terminal 30 by causing the low-pass filter 70 to wave this rectangular wave. The amplitude of the rectangular wave or the amplitude of the sine wave V _pp is V _pp = R · i, where R is the resistance value of the load resistor 44 and i is the current value flowing through the current source circuit 50.

As described above, the amplitude V _pp of the output signal is determined by the resistance value R of the load resistor 44 and the operating current i. Therefore, the value of the digital signal supplied to the DA converter 60 is changed to change the current value i of the current source circuit 50. As a result, the amplitude V _pp of the output signal of the differential amplifier 40 can be changed.

Therefore, by changing the digital value given to the DA converter 60 at a predetermined pitch, the amplitude V _{pp of the} output signal can be changed in association with the change in the digital signal with the pitch. Therefore, the signal level can be changed with high accuracy.

Further, especially since the differential amplifier 40 operates as a saturation amplifier, the amplitude of the output signal does not change even if the value i of the current flowing through the current source circuit 50 does not change even if the level of the reference signal supplied from the reference signal source 10 changes. do not do.

Therefore, a highly stable and highly accurate calibration signal can be output to the output terminal 30.

“Effect of device” As described above, according to this device, the reference signal source 10 and
Since the DA converter 60, the differential saturation amplifier 40, the current source circuit 50, and the low-pass filter 70 as necessary, can constitute a level calibration signal source, and most of them can be constituted by electronic circuit elements. It can be made cheaper than the conventional attenuator configuration using a relay and a high precision resistor.

However, since the stability of the calibration signal is specified by the stability of the analog signal obtained by DA converting the digital signal, high stability can be obtained.

Further, since the step of changing the level of the calibration signal can be determined by the digital signal given to the DA converter 60, the changing step can be accurately determined.

Therefore, a level calibration signal source having high stability and high signal level setting accuracy can be manufactured at low cost, and its effect is great for practical use.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, and FIG. 2 is a connection diagram for explaining a conventional technique. 10: reference signal source, 40: differential type saturation amplifier, 50: current source circuit, 60: DA converter.

Claims (1)

[Scope of utility model registration request] 1. A differential-type saturation amplifier which outputs a reference signal for level calibration to one input terminal and outputs the amplified output as a reference-level signal, and B. an operating current of the differential-type saturation amplifier. A signal source for level calibration composed of a current source circuit that regulates C. and a DA converter that controls the current value of this current source circuit.