JPH0666603B2 - Spectral signal amplifier for time-of-flight mass spectrometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a spectrum signal amplifier for a time-of-flight mass spectrometer.

<Prior Art> In a time-of-flight mass spectrometer, a spectrum signal output from an ion detector, which is generally a series of pulse waveform signals, is amplified to an appropriate level and then subjected to A-D conversion to obtain a spectrum signal. The method of analyzing is taken. An AC coupling type amplifier is often used to amplify the spectrum signal. By the way, when it is necessary to detect the waveform of the spectrum particularly accurately, the frequency band of the amplifier must be sufficiently wide, but in the AC coupling type amplifier, the waveform is distorted due to the differential characteristic of the coupling portion, The weak signal that immediately follows the large signal is affected in no small way.

Therefore, it is desirable to use the DC coupling type wide band amplifier in consideration of the case where the spectrum waveform needs to be accurately detected, but the DC coupling type is not suitable for long-term use due to the problem of zero drift.

<Problems to be Solved by the Invention> By the way, when a very weak spectrum included in a series of spectrum signals is detected, ion acceleration is repeated many times and a spectrum signal obtained each time is integrated. Is adopted.

At that time, if there is a relatively large spectrum adjacent to the weak spectrum to be detected, when an AC coupling type amplifier is used, a slight waveform distortion occurs in the amplified signal waveform of the large spectrum at each amplification. Are also accumulated, which may interfere with the detection of the weak spectrum that is the object of detection. Further, in the DC-coupled amplifier, zero-point drift progresses while the ion acceleration is repeated many times over a long time, impairing the dynamic range of the measuring section, and when using with a large gain, A -D
The input voltage of the converter may go out of the convertible range, which makes it impossible to detect a (weak) signal.

The present invention provides a solution to the above-mentioned difficult problems associated with the detection of weak spectral signals contained in a series of spectral signals.

<Means for Solving Problems> In order to solve the problems, a spectrum signal amplifier for a time-of-flight mass spectrometer according to the present invention is a DC amplification circuit for amplifying a signal for amplifying an output of an ion detector, and The value of the signal output by the switching circuit for switching the input terminal between the ground circuit side and the output side of the ion detector, and the DC amplification circuit for signal amplification while the ground circuit is connected to the input terminal. That is, the signal value holding circuit that holds the zero drift value at that time, and the signal that the DC amplification circuit outputs while the output of the ion detector is input to its input terminal and the signal value holding circuit. And a differential amplifier circuit that outputs a difference signal from the output signal of 1., and the amplified spectrum signal is output from the differential amplifier circuit.

<Operation> In the above-described configuration of the spectrum signal amplifier, the switching circuit is synchronized with the repeating cycle of the ion acceleration detection operation of the mass spectrometer, to the output side of the DC amplification circuit during the period when the ion acceleration detection is performed, Also, by switching to the ground circuit side alternately during the waiting period until the next ion acceleration detection, the output of the DC amplifier circuit during the waiting period of ion acceleration is the output with respect to the input zero at that time, that is, zero drift. Indicates a value. This value is held by the signal holding circuit until the DC amplification circuit is connected to the ion detector side at the time of the next ion acceleration and the spectrum signal is amplified and output. By the way, the zero drift value of the same DC amplification circuit is superimposed on the amplified spectrum signal at the output of the DC amplification circuit at the time of amplifying the spectrum signal. The difference in the zero drift values held by
Output only the spectral signal component. This subtraction operation of the zero drift value is performed every time the ion acceleration is performed, that is, every time when the spectrum signal is detected, by using the zero drift value of the DC amplification circuit immediately before that, and therefore, the output of the differential amplification circuit, that is, ,
The output of the DC amplifier is not affected by the zero drift of the DC amplification circuit portion and is always an amplified spectrum signal.

<Examples> Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a spectrum signal amplifier 9 for a time-of-flight mass spectrometer according to an embodiment of the present invention (a portion surrounded by a chain line).
And the input side of the amplifier 9 is connected to the ion detector 10 of the ion acceleration detector, and the output side is the AD converter 11
Shows the state of being connected to. In this figure, a spectrum signal amplifier 9 includes a wide band direct current amplification circuit 2 for amplifying a spectrum signal, a differential amplification circuit 3 with an amplification degree of 1 for removing a zero drift signal of the amplification circuit system, and a signal holding circuit 4. It is composed of two differential amplifier circuits 5 and 7 with an amplification factor of 1, two changeover switches 1 and 6, and a reference DC voltage power source 8 for detecting the zero drift signal.

In the above configuration, when both the changeover switches 1 and 6 are switched to the ground side, the DC amplification circuit 2 outputs the zero lift value Ed at that time (point P), and the value is the differential amplification circuit 3 ( It is input to the inverting input terminal with an amplification of 1). On the other hand, the reference DC voltage E ₀ (point T) from the reference DC power supply 8 is input to the non-inverting input terminal of the differential amplifier circuit 3 from the output side of the differential amplifier circuit 7 (amplification degree 1). . Therefore,
On the output side of the differential amplifier circuit 3, the zero drift value Ed ′ of the amplifier circuit 3 itself is superimposed and the voltage −Ed + Ed ′ + E ₀ is output (point Q). This value is kept unchanged by the signal holding circuit 4 (point R) and input to the non-inverting input terminal of the differential amplifier circuit 5 (amplification degree 1). On the other hand, the reference DC voltage E ₀ to the inverting input terminal of the differential amplifier circuit 5 is input, the output side of the differential amplifier circuit 5, -Ed + Ed '+ voltage E E ₀ than ₀ is subtracted -Ed + Ed 'will be maintained (S
point).

Next, when the switches 1 and 6 are both switched to the non-grounded side, the differential amplifier circuit 7 having the reference DC voltage E ₀ input to the non-inverting input terminal has the differential amplifier circuit 5 at its inverting input terminal.
Output side voltage −Ed + Ed ′ is input, and voltage Ed−Ed ′ + E ₀
On the other hand, the input side of the DC amplification circuit 2 is connected to the ion detector 10 side, and the amplification value Es of the spectrum signal Es is output.
The value Es + Ed with the zero drift value superimposed on is output. Therefore, the differential amplifier circuit 3 has a voltage Es +
Since Ed is input and the voltage Ed−Ed ′ + E ₀ is input to the non-inverting input terminal, (Ed−Ed ′ + E ₀ ) − (Es + Ed) + Ed ′ = − Es + E ₀ is output. This output value is the amplified spectral signal Es
(However, the sign is inverted) and the reference DC voltage E _{0 only} , and the zero drift values Ed and Ed ′ of the DC amplification circuit 2 and the differential amplification circuit 3 are not included. However, in the above description, the zero drift of the differential amplifier circuits 5 and 7 is not taken into consideration. The reason is that these differential amplifier circuits are circuits that process only the DC voltage and the frequency band thereof is The width can be extremely narrow, and therefore, it can be configured with circuits that consume little power and generate very little heat. Therefore, the zero drift of these circuits is required to have an extremely wide band characteristic from DC to high frequency. This is because the zero drift of the amplifier circuit 2 and the differential amplifier circuit 3 can be practically completely ignored. If it is not necessary to superimpose the reference DC voltage E _{0 on} the spectrum signal Es, the line connected to the reference DC power supply 8 may be grounded.

As described above, according to the above-described embodiment, the influence of the zero drift is removed from the output signal by the changeover operation of the changeover switches 1 and 6, so that if both changeover switches are operated in synchronization with the repetition of the ion acceleration detection, a long operation is possible. The correct spectral signal can always be detected over time. However, in the drawing, the configurations of the changeover switches 1 and 6 are both mechanically expressed in order to avoid complication, but in order to operate in synchronization with the ion acceleration operation, a switching element or circuit formed of a known electronic circuit is used. Of course, it should consist of

It should be noted that FIG. 2 shows a time chart for explaining the switching operation of the changeover switches 1 and 6 in synchronization with the ion acceleration detection.

<Effects of the Invention> As is clear from the above description, by employing the DC coupling type spectrum signal amplifier according to the present invention, it becomes easy to detect a weak spectrum adjacent to a strong spectrum.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of the changeover switch used in the embodiment of the present invention. 1,6 ...... Selection switch 2 ...... Spectral signal amplification circuit 3 ...... Differential amplification circuit for zero drift signal subtraction 4 …… Signal holding circuit 5,7 …… Differential amplification circuit for zero drift signal detection 8 …… Reference DC voltage power supply

Claims (3)

[Claims] 1. A time-of-flight mass spectrometer, which is an amplifier for amplifying an output signal of an ion detector, wherein a DC coupling type ion signal amplifying circuit and a signal input terminal of this ion signal amplifying circuit are used for the ion detection. A first switching circuit for switching between an output terminal of the instrument and a ground circuit, and a first switching circuit for setting an output signal of the ion signal amplification circuit as a first input signal
Differential amplifier circuit, a signal holding circuit that holds the output signal value of the first differential amplifier circuit, and a second differential amplifier circuit that uses the output signal of the signal holding circuit as the first input signal. , A second switching circuit that switches the output between the output of the second differential amplifier circuit and the ground circuit, and a third differential circuit that uses the output signal of the second switching circuit as the first input signal. An amplifier circuit, and the output of the third differential amplifier circuit is input to the first differential amplifier circuit as a second input signal, and the second differential amplifier circuit has a second input signal. A spectrum signal amplifier for a time-of-flight mass spectrometer, wherein the input signal and the second input signal of the third differential amplifier circuit are a common reference DC voltage having a predetermined value. 2. The first differential amplifier circuit, the second differential amplifier circuit, and the third differential amplifier circuit are all differential amplifier circuits having an amplification degree of 1. A spectrum signal amplifier for a time-of-flight mass spectrometer according to claim 1. 3. The spectrum signal amplifier for a time-of-flight mass spectrometer according to claim 1 or 2, wherein the reference DC voltage is zero volt.