JP2000258489A - Measuring device of mutual conductance and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compute the higher-order strain component of mutual conductance by inputing sine wave superimposed with DC current to FET as gate voltage, and analyzing a digital voltage signal converted from drain output current. SOLUTION: When sine wave from a signal source 3 superimposed with DC current by a power supply 4 for bias is input to FET 1, drain current is outputted from the FET 1. The drain current is amplified, converted to a voltage signal by a current/voltage converter 6, the signal level is regulated by a level regulater 8, and input to an A/D converter 7. The input signal to the A/D converter 7 is sampled with a cycle so as to be divided into 2N (N is an integer, N >7 is desirable) for the input sine wave frequency to the FET 1, and converted to a digital signal. The digital signal is input to a personal computer 9 to be analyzed through Fourier transform. As a result of this, the voltage signal input to the A/D converter 7 can detect not only the basic wave component, but the higher-order strain component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for measuring the transconductance of a field effect transistor.
The present invention relates to an apparatus and a method for measuring the transconductance of a field-effect transistor for detecting higher-order distortion components by fast Fourier transform.

[0002]

2. Description of the Related Art Conventionally, a field effect transistor (hereinafter referred to as F
Called ET. By measuring the mutual conductance of (2), the static characteristics and the like of the FET were examined. The transconductance is a coefficient indicating a relationship between an input voltage signal and an output current signal. If the transconductance contains many high-order distortion components, the output signal of the amplifier to which the FET is applied also contains many high-order distortion components.

[0003] Therefore, when an FET is used in an apparatus or the like that requires severe distortion characteristics, it is necessary to examine the mutual conductance of the FET and its higher-order distortion components.

Therefore, in the conventional technique, the gate voltage input to the gate terminal of the FET is increased monotonously and stepwise, and the drain current output from the drain terminal at that time is sampled for each voltage step. Then, the transconductance is measured by calculating the ratio between the change amount of the gate voltage and the change amount of the drain current.

That is, the change amount of the gate voltage is represented by ΔV _GS ,
Assuming that the amount of change in the drain current is ΔI _D , the transconductance g _m can be expressed as g _m = △ I _D / △ V _GS . The measurement of the transconductance g _m is realized by a dedicated measuring instrument.

[0008] FIG. 8 shows a conventional measurement method generally used.
FIG. With this measuring instrument,
G_mIs measured, for example, by VR_TwoV
_DSWhile maintaining the constant₁And change V_GSUsually
I when changing stepwise at a new voltage interval_DRead
Take it. In this way, as shown in FIG.
Gate-source voltage V of ET _GS-I_DHave the characteristics
Was. In FIG. 9A, each V_GSEvery step of
And the corresponding I_DAnd take V_GSStep voltage and
Is plotted, as shown in FIG._GS
-G_mA diagram showing the characteristics is obtained. And in the traditional way
In order to obtain the distortion component of the transconductance, FIG.
In (b), each V _GSFor each step of_m
And take V_GSOf the step voltage of the
Was. To calculate higher-order distortion components,
V_GSBy taking the difference for each step of
Good.

In order to obtain a higher-order distortion component, it is necessary to precisely measure the change in the transconductance. Therefore, it is necessary to finely change the step change amount of the gate voltage. That is, it is necessary to reduce the step of the gate voltage.

[0008]

However, in the prior art, if the step of the gate voltage is made very small, many measurement errors and the like occur. Therefore, even if the step of the gate voltage is made very small, it is difficult to improve the measurement accuracy of the higher-order distortion component of the transconductance.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to calculate a high-order distortion component of transconductance without reducing the steps of the gate voltage.

[0010]

In order to solve the above-mentioned problems, the present invention relates to an apparatus for measuring the transconductance of a field effect transistor, which generates a sine wave and inputs the sine wave to a gate terminal of the field effect transistor as a gate voltage. A signal source, an amplitude detecting means for detecting an amplitude component of the sine wave, a bias power supply for superimposing a DC voltage on the sine wave, and converting a drain current output from a drain terminal of the field effect transistor into a voltage signal. Current / voltage converting means, an A / D converter for converting the converted voltage signal into a digital signal, component detecting means for detecting a fundamental wave component and each higher-order distortion component from the digital signal,
Dividing means for dividing the fundamental wave component and the respective higher-order distortion components by the amplitude component of the sine wave.

The present invention also provides a method for measuring the transconductance of a field effect transistor, comprising the steps of generating a sine wave, inputting the sine wave to a gate terminal of the field effect transistor as a gate voltage, detecting an amplitude component of the sine wave, A DC voltage is superimposed on a sine wave, a drain current output from a drain terminal of the field-effect transistor is converted into a voltage signal, the converted voltage signal is converted into a digital signal, and a fundamental wave component and A higher-order distortion component is detected, and the fundamental wave component and each of the higher-order distortion components are divided by the amplitude component of the sine wave.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

[0013] (Embodiment 1) FIG. 1 is a diagram showing a measuring apparatus for measuring the transconductance g _m which contains a distortion component of the present embodiment. Embodiment 1 will be described with reference to FIG.

As shown in FIG. 1, the gate terminal of the FET 1 is connected through a capacitor 2 to a signal source 3 for generating and outputting a sine wave. The capacitor 2 cuts a DC component of a sine wave output from the signal source 3. A bias power supply 4 for superimposing a DC voltage on a sine wave is connected to the gate terminal of the FET 1.

The drain terminal of the FET 1 is connected to a current amplifier 5 for amplifying a drain current _ID . The output side of the current amplifier 5 is connected to a current / voltage converter 6 for converting the drain current _ID into a voltage signal. Current /
The output side of the voltage converter 6 is connected to a level adjuster 8 that adjusts the voltage to an amplitude level that can be converted by the A / D converter 7.

The output side of the A / D converter 7 is connected to a personal computer 9 for performing a fast Fourier transform (FFT) of the digital signal. The sine wave input from the signal source 3 to the FET 1 is input to the personal computer 9 through the level detector 10 for detecting the amplitude level of the sine wave. In addition,
In the personal computer 9, by simply performing the Fourier transform,
Higher-order distortion components may be calculated.

Next, the operation of the measuring apparatus shown in FIG. 1 will be described.

The sine wave output from the signal source 3 passes through the capacitor 2 and the gate voltage V
_Entered as _G. Gate voltage V _G is one that is minutely amplitude. An external bias power supply 4
, A DC voltage is superimposed. Therefore, the gate voltage V _G would have an amplitude about a DC voltage.

[0019] Upon entering the gate voltage V _G, the drain current I _D from the drain terminal of the FET1 is output. The drain current _ID is amplified by the current amplifier 5. Then, it is converted into a voltage signal by the current / voltage converter 6,
The level of the voltage signal is adjusted by the level adjuster 8. As described above, the level adjuster 8 controls the A / D converter 7.
The voltage level of the voltage signal is adjusted to the input voltage range of FIG. Thereafter, the level-adjusted voltage signal is A / D
It is input to the converter 7.

The voltage signal input to the A / D converter 7 is
It is sampled at an arbitrary sampling period and converted into a digital signal. Here, the sampling period is, for example, the frequency of the input voltage signal, that is, the FET 1
Is divided into 2 ^N (N is an integer, N> 7 is preferable here) with respect to the frequency of the sine wave input to the gate terminal. Moreover, by finely sampling period may be determined higher order distortion components of the transconductance g _m.

The digital signal is input to the personal computer 9 and analyzed by fast Fourier transform (hereinafter, referred to as FFT). As a result, the voltage signal input to the A / D converter 7 can detect not only the fundamental component but also a higher-order distortion component.

Here, the FFT analysis in the personal computer 9 will be described by taking as an example a case where an AlGaAs / InGaAs-based heterojunction FET is used as the FET 1 and its mutual conductance is measured.

A sine wave signal having an input amplitude of 100 mV is applied to the gate terminal of the FET 1 having a gate width of 100 μm. The frequency of the sine wave is 10 kHz. Further, -0.5 V is applied as an external bias voltage applied to the gate terminal of FET1.

By the sine wave input to the gate terminal, F
A current waveform as shown in FIG. 2 is obtained as the drain current of ET1. FIG. 3 shows a digital signal obtained by inputting the drain current to the A / D converter 7 through the current amplifier 5, the current / voltage converter 6, and the level adjuster 8.
At this time, the sampling frequency of the A / D converter 7 is 5.12 MHz.
z, that is, a frequency at which the input signal 10 kHz is divided into 512. The A / D converter 7 has a resolution of 10 bits.

If the voltage level of the voltage signal is adjusted by the current amplifier 5, the current / voltage converter 6, and the level adjuster 8 so as not to exceed the input voltage range of the A / D converter 7, a digital signal obtained is obtained. Is 0 as shown on the vertical axis of FIG.
It becomes an integer of ２３1023.

In the personal computer 9, a digital signal corresponding to one cycle of the input sine wave (51 corresponding to the number of divisions) is output.
FFT analysis is performed by taking in two data).

Of the various components of the voltage signal obtained by the FFT analysis, all of the components except the DC component include the drain current output from the drain terminal, the current amplifier 5, the current / voltage converter 6, and the level adjuster 8. Is converted through

On the other hand, the level of the gate voltage input to the FET 1 is detected by the level detector 10 and this value is input to the personal computer 9. In the personal computer 9, the drain signal is obtained by multiplying the voltage signal obtained from the FFT analysis by the reciprocal of each coefficient set in the current amplifier 5, the current / voltage converter 6, and the level adjuster 8.

[0029] Here, the drain current I _D and the gate voltage V _G
Then, the mutual conductance of the FET 1 is calculated. That is, the mutual conductance g of the FET 1
_m is the ratio of the amount of change in the gate voltage V _G which is input from the gate terminal and the variation of the drain current I _D to be output accordingly.

Therefore, the change amount of the gate voltage is Δ
Assuming that V _G and the amount of change in drain current are ΔI _D , the transconductance g _m can be expressed as g _m = △ I _D / △ V _G.

Further, in the present embodiment, since each high-order distortion component of the drain voltage is obtained by performing the FFT analysis in the personal computer 9, the ratio between the magnitude of the drain current _{ID and} the magnitude of each high-order distortion component is calculated. By calculating, the distortion component of the transconductance g _m can be obtained. The result is shown in FIG.

The case where the transconductance g _m at one gate voltage is obtained has been described above.
By varying the magnitude of the DC voltage to be superimposed on the sine wave by the bias power source 4, by varying the magnitude of the gate voltage V _G, by repeating the above method, the transconductance g in each of the gate voltage V _{G m} can be measured.

In this way, when the FET 1 is used as an amplifier, bias conditions such as a gate voltage and a drain voltage can be predicted in advance so that the distortion characteristics become good.

[0034] Figure 5, the drain voltage of the FET1 to each of the gate voltage V _G - is a diagram showing the drain current characteristic. In FIG. 5, the symbol ● indicates the mutual conductance g.
_The measurement points for measuring _m are shown.

As shown in FIG. 5, in this embodiment, the FET
1 of the voltage - current characteristic, on the so-called I _D -V _DS curve,
Drain - when the source voltage V _DS is constant, by varying the magnitude of the drain current I _D, measures the transconductance g _m which includes a distortion component in each of the gate voltage V _G.

(Embodiment 2) FIG. 6 is a view showing an apparatus for measuring a transconductance including a distortion component according to the present embodiment. Embodiment 2 will be described with reference to FIG.

In FIG. 6, reference numeral 11 denotes a load resistor connected to the drain terminal of the FET 1, reference numeral 12 denotes a power supply terminal connected to the load resistor 11, and reference numeral 13 denotes a voltage amplifier for amplifying a drain voltage converted by the load resistor 11. The same members as those in the first embodiment are denoted by the same reference numerals.

Next, the operation of the measuring apparatus shown in FIG. 6 will be described. The operation similar to that of the first embodiment will be briefly described. First, as in the first embodiment, a gate voltage on which a DC voltage is superimposed by an external bias power supply 4 is input to the gate terminal of the FET1, and a drain current _ID is output from the drain terminal of the FET1.

The drain current _ID is converted into a drain voltage at a connection point between the drain terminal and the load resistor 11 by the load resistor 11 and the power supply voltage 12 connected to the drain terminal. The drain voltage is amplified by the voltage amplifier 13. Then, the level of the voltage signal is adjusted by the level adjuster 8 and input to the A / D converter 7.

The voltage signal input to the A / D converter 7 is
It is sampled at an arbitrary sampling period and converted into a digital signal. The digital signal is input to the personal computer 9 and subjected to FFT analysis. As a result, the voltage signal input to the A / D converter 7 has not only its fundamental wave,
Each higher-order distortion component can also be determined.

The difference between the present embodiment and the first embodiment is that
Transconductance g _mHow to measure
You. In the first embodiment, the drain-source voltage of the FET 1 is
Pressure V_{D S}And the gate voltage V of the FET 1_GThe size of
The drain current I_DSize of
To change the transconductance g including the distortion component._m
Is measured.

On the other hand, in the present embodiment, by varying the magnitude of the gate voltage V _G, the drain current I a magnitude varied and _D, the drain of the FET1 due to a voltage drop caused by the load resistance 11 - source voltage V the size of the _DS also changed, to measure the transconductance g _m including distortion components.

[0043] While there has been a description of the case of obtaining the mutual conductance g _m of one gate voltage V _G, by varying the magnitude of the DC voltage to be superimposed on the sine wave by the bias power source 4, a gate voltage V by varying the size of _G, by repeating the above method, it is possible to measure the transconductance g _m of each of the gate voltages.

Thus, when the FET 1 is used as an amplifier, it is possible to predict in advance bias conditions such as a gate voltage and a drain voltage at which the distortion characteristics are good.

[0045] Figure 7, the drain voltage of the FET1 to each of the gate voltage V _G - is a diagram showing the drain current characteristic. In FIG. 7, the symbol ● indicates the mutual conductance g.
_The measurement points for measuring _m are shown. When the drain current I _D is increased by increasing the gate voltage V _G, the drain voltage is reduced by a voltage drop due to the load resistance 11. On the other hand, when the drain current I _D is reduced by reducing the gate voltage V _G, the drain voltage is increased by the voltage drop due to the load resistance 11.

[0046] Therefore, it becomes possible to bias conditions vary substantially straight line in a so-called load line, when using the FET1 as amplifiers, in a state close to actual operating conditions, the distortion component in each of the gate voltage V _G The transconductance is measured.

[0047]

As described above, according to the present invention,
A sine wave obtained by superimposing a DC voltage on a field-effect transistor is input as a gate voltage, the drain current output thereby is converted into a voltage signal, and the converted voltage signal is converted into a digital signal. Each higher-order distortion component including a fundamental wave component is detected.

Therefore, since the distortion characteristic of the mutual conductance of the FET can be obtained in advance,
Before using as an amplifier, one can determine if it is a good device.

[Brief description of the drawings]

FIG. 1 is a diagram showing an apparatus for measuring a transconductance including a distortion component according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a drain current waveform obtained by the measuring device of FIG.

FIG. 3 is a diagram showing characteristics after A / D conversion obtained by the measuring device of FIG. 1;

FIG. 4 is a diagram showing a transconductance characteristic obtained by the measuring device of FIG. 1;

FIG. 5 is a diagram showing a drain current _ID -drain voltage _VDS characteristic obtained by the measuring device of FIG. 1;

FIG. 6 is a diagram illustrating a transconductance measuring device including a distortion component according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a drain current _ID -drain voltage _VDS characteristic obtained by the measuring device of FIG. 3;

FIG. 8 is a diagram showing a conventional transconductance measuring device.

The drain current obtained by the measurement apparatus of FIG. 9] FIG. 8 I _D - gate voltage V _G characteristics and transconductance g _m -
It is a diagram showing the gate voltage V _G characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 FET 2 Capacitor 3 Signal source 4 Power supply for bias 5 Current amplifier 6 Current / voltage converter 7 A / D converter 8 Level adjuster 9 Personal computer 10 Detector 11 Load resistance 12 Power supply voltage 13 Voltage amplifier

Claims (8)

[Claims] 1. An apparatus for measuring the transconductance of a field effect transistor, comprising: a signal source for generating a sine wave and inputting the sine wave to a gate terminal of the field effect transistor as a gate voltage; and an amplitude detecting means for detecting an amplitude component of the sine wave. A bias power supply for superimposing a DC voltage on the sine wave; current / voltage conversion means for converting a drain current output from a drain terminal of the field effect transistor into a voltage signal; and digitally converting the converted voltage signal. A to convert to signal
/ D converter, component detection means for detecting a fundamental wave component and each higher-order distortion component included in the digital signal, and detecting the detected fundamental wave component and each of the higher-order distortion components.
A dividing means for dividing the detected sine wave by an amplitude component of the detected sine wave. 2. The apparatus according to claim 1, wherein the current / voltage conversion unit is a load resistance. 3. The apparatus according to claim 1, wherein the component detection unit performs a Fourier transform analysis. 4. The apparatus according to claim 1, wherein the gate voltage is variable. 5. A method for measuring a transconductance of a field effect transistor, comprising: generating a sine wave, inputting the sine wave to a gate terminal of the field effect transistor as a gate voltage, detecting an amplitude component of the sine wave, Superimposing a voltage, converting a drain current output from a drain terminal of the field-effect transistor into a voltage signal, converting the converted voltage signal into a digital signal, and converting a fundamental wave component and each higher-order distortion from the digital signal. A method for measuring the transconductance of a field effect transistor, comprising: detecting a component; and dividing the fundamental component and each of the higher-order distortion components by an amplitude component of the sine wave. 6. The method according to claim 5, wherein the drain current is converted into the voltage signal by a load resistance. 7. The method according to claim 5, wherein the fundamental component and each of the higher-order distortion components are detected by performing a Fourier transform analysis. 8. The method according to claim 5, wherein the gate voltage is variable.