JPH04101505A - Amplifier - Google Patents

Abstract

PURPOSE:To change the gain of an amplifier by using a photomultiplier to adjust the voltage applied from a variable voltage source to a potential resistor. CONSTITUTION:When the beam of light is made incident on a sensor 4, a current is generated in proportion to the quantity of incident light and the same quantity of photoelectron as the generated current is discharged from the cathode electrode 1k of photomultiplier 1. Further, the photoelectron discharged from the cathode electrode 1k is multiplied by the diode electrode 1d at each stage, is then caught by an anode electrode 1a, becomes a current, and is further input to an operational amplifier 3. The gain of photomultiplier 1 can be considerably changed by adjusting the voltage that adjusts the variable voltage source 2 and is applied to the potential resistor R, or the voltage that is applied to the cathode electrode 1k and mutually to diode electrodes 1d at each stage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an amplifier whose gain can be adjusted significantly while maintaining linearity with respect to input and output signals.

(Prior art) In optical temperature measuring devices such as color thermometers and brightness thermometers,
When a solar cell or a PIN photo guioto is used as a sensor, a multi-stage transistor amplifier or an IC amplifier is used as an amplifier to amplify the output of the sensor, which serves as a signal current generation source.

(Problem to be solved by the invention) The amount of light that enters the solar cell and PIN photo guide that serve as the sensor changes significantly, from a weak amount of light to tens of thousands of λ, and the output of the sensor also changes significantly. If you try to amplify the output using a normal amplifier, it is extremely difficult to adjust the gain of the amplifier over a wide range of 100 db or more, so there is a limit to the amount of incident light that can be tolerated. If the amount of incident light was too large, it had to be limited by an aperture.

(Means for Solving the Problems) Therefore, the present invention was devised to solve such problems, and uses a photomultiplier tube as an amplifier. It utilizes a wide range of gain adjustment functions.

(Technology on which the invention is based) As shown in FIG. 3, the photomultiplier tube 1 includes a cathode electrode 1 having a photocathode that emits photoelectrons when light 10 is incident thereon, and a plurality of stages of dynode electrodes 1d. , one anode electrode 1a.

In normal use, the entire dynode electrode 1d is connected to the cathode electrode 1 through a voltage dividing resistor R connected in series.
A variable voltage source 2 applies a voltage that increases sequentially to the voltage. Then, when light enters the cathode electrode 1k,
Since the cathode electrode 1 emits photoelectrons proportional to the amount of incident light, the number of photoelectrons increases each time the photoelectrons collide with the dynode electrode 1d of each adjacent stage, and is finally captured by the anode electrode 1a. It is.

Then, a load resistance R connected to this anode electrode 1a
An output voltage proportional to the amount of incident light is obtained from L.

In this way, in the photomultiplier tube 1, the amount of light incident on the cathode electrode 1k is small, and even if the number of emitted photoelectrons is small,
The number of electrons captured by the anode electrode 1a increases, and the anode electrode 1a has a high gain amplification function.

By adjusting the voltage applied from the variable voltage source 2 to the voltage dividing resistor R, it is possible to significantly change the multiplication factor from 102 to 1011 times.

(Example) As shown in FIG. 1, a voltage increasing sequentially is applied to all dynode electrodes 1d through a voltage dividing resistor R connected in series to a variable voltage source 2. A photomultiplier tube 1 is used, and between the cathode electrode 1 of the photomultiplier tube 1 and the variable voltage source 2, a solar cell or a PI, which serves as a signal current generation source, is connected.
A sensor 4 such as an N photodiode is connected, and the anode electrode 1a is connected to an operational amplifier 3 that converts current into voltage.
is connected to the input terminal of

A light source 5 such as a light emitting diode is provided which always irradiates a constant amount of light onto the cathode electrode 1k.

The output of the operational amplifier 3 is used for signal processing and is led to the peak detection circuit 8.
The peak value output of
The difference between the two is fed back to the variable voltage source 2 to form an automatic gain control system that adjusts the generated voltage.

For example, an amplifier including the photomultiplier tube 1 of the present invention may be used, for example.
When applied to a color thermometer, two types of filters 6a with different passing wavelengths λa and λb are provided in the middle of the optical path of incidence to the solar cell or PIN photodiode serving as the sensor 4.
A rotary filter 6 having a diameter of 6b and rotated by a motor 7 is provided.

(Operation) When no light beam is incident on the sensor 4, which is the signal current generation source, the sensor 4 does not generate any current, so the light source 5 connects the cathode electrode 1 of the photomultiplier tube 1.
Even if a certain amount of light is irradiated onto k, no current can flow, so the cathode electrode 1 does not emit photoelectrons.

However, when a light beam is incident on the sensor 4, a current proportional to the amount of the incident light is generated, and the cathode electrode 1 of the photomultiplier tube 1 emits photoelectrons of the same amount as the generated current. The photoelectrons emitted by the cathode electrode 1 are
After being multiplied by the dynode electrode 1d of each stage, it is captured by the anode electrode 1a, and is turned into a current and inputted to the operational amplifier 3.

At this time, the current generated from the anode electrode 1a of the photomultiplier tube 1 is proportional to the amount of light incident on the sensor 4, and is also proportional to the gain of the photomultiplier tube 1.

The gain of the photomultiplier tube 1 is determined by adjusting the variable voltage source 2 to adjust the voltage applied to the voltage dividing resistor R, that is, the voltage applied to the cathode electrode 1 and between the dynode electrodes 1d of each stage. By doing so, the gain is 102~1011
Therefore, even if the light beam incident on the sensor 4 changes significantly, it can be amplified with the optimum gain by adjusting the voltage generated by the variable voltage source 2.

For example, in a color thermometer, 2
Since the color temperature is determined by the ratio of the intensities of the two wavelengths λa and λb, even if the amount of incident light is small and the output signal is small as shown in Figure 2A,
As shown in , even if the amount of incident light is large and the output signal is large, if the ratio a/b of the intensities a and b of the two wavelengths λa and λb is the same, the same color temperature must be specified. As an amplifier, linearity must be maintained accurately no matter what gain it operates at.

However, according to the amplifier of the present invention, two signals having the same ratio but different strengths can be amplified so that the peak value reaches a constant level while maintaining the ratio accurately.

The embodiments in which the amplifier of the present invention is applied to a color thermometer have been described above, but the present invention can also be applied to amplifiers that amplify various other signals.

(Effects) As described above, according to the amplifier of the present invention, not only AC signals but also DC signals can be amplified while maintaining linearity with respect to input/output signals while significantly changing the gain.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the amplifier of the present invention;
FIG. 2 is a waveform diagram used to explain the operation of the amplifier shown in FIG. 1, and FIG. 3 is a circuit diagram used to explain the technology underlying the amplifier of the present invention. ...Photomultiplier tube ...Variable voltage source ...Operation amplifier ...Sensor (signal current generation source) ...Light source ...Rotating filter ...Motor ...Peak detection circuit ...Comparison Circuit Figure 1 Figure 3 Figure 2 A Figure 2 B

Claims (1)

[Claims] (1) A photomultiplier tube equipped with a cathode electrode equipped with a photocathode that emits photoelectrons when light is incident, multiple stages of dynode electrodes, and an anode electrode, and a voltage that increases sequentially is applied to the multiple stages of dynode electrodes. a voltage dividing resistor connected in series, a variable DC voltage source that adjusts the gain of the photomultiplier tube by changing the voltage applied to the voltage dividing resistor, and a connection between the variable DC voltage source and the cathode electrode. an amplified signal current generating source, and a light source that makes a substantially constant light beam incident on the cathode electrode, and the amplifier is characterized in that the current from the signal current generating source is derived from the anode electrode as an amplified current. .