JPH0664118B2 - Transistor characteristics measurement circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transistor characteristic measuring circuit, and more particularly to a measuring circuit used for measuring the base voltage-collector current characteristic of a transistor (bipolar transistor).

[Conventional technology]

In the case where the bipolar transistor has a grounded emitter, when the dependence of the collector current I _c of the base-emitter voltage V _BE is measured, I _c is substantially proportional to the exponential function of V _BE , and I _c = I It is known that it is expressed as ₀ · exp (eV _BE / nkT) (1). The coefficient n of the denominator of the argument of the exponential function at that time is a parameter indicating the deviation of the characteristic from the ideal value.

It is known that this n becomes 1 when the transistor is operating in the low injection state, but shifts to a value larger than 1 as the current increases and approaches the high injection state. . Therefore, by knowing this value of n, it is possible to grasp in what state the transistor being measured operates.

Therefore, it is necessary to obtain the value of n in the measurement and evaluation of the transistor. Conventionally, the value of n of the transistor is determined from the voltage-current characteristics measured by the measuring circuit shown in FIG. It has been. In the case of the circuit of FIG. 3, the base voltage of the transistor 11 is set by the adjustable DC voltage source 42 and the collector voltage is set by the operational amplifier 45 so that it is equal to the voltage of the DC voltage source 41. The collector current I _c is read by the ammeter 43 connected to the collector terminal 3.

The logarithm of the collector current I _c as measured by a circuit such as Figure 3
The logI _c is plotted against the base-emitter voltage V _BE at that time as shown in FIG. 4, and n can be obtained from the slope of the straight line drawn so as to apply to it. For example, in the case of FIG. 4, V _BE at points A and B is V _a ,
And V _b, also the _{I c} respectively _I a, when a _{I b, n = (e /} kT) · (V a -V b) / ((log (I a) -log (I b)) ... ( 2) Therefore, from each value of V _a , V _b , I _a , and I _b , (2)
The value of n is calculated based on the equation.

[Problems to be solved by the invention]

However, in this case, it is necessary to set the voltage and read the current a plurality of times in order to extract n as a parameter.

For example, referring to the example of FIG. 3, the base-emitter voltage V _BE is set to V _a by adjusting the DC voltage source 42, and
The collector current I _a in this state is read by the ammeter 43,
Further reconfigure this by adjusting the voltage V _BE between the base and emitter again V _b, it is necessary to read the collector current I _b of the time.

As described above, in the above-described conventional example, when the parameter n is determined from the voltage / current characteristics of one transistor, the ammeter reading and the adjustment of the voltage source are performed a plurality of times.
It had to be done manually or by the control computer. Therefore, the measurement of this value becomes complicated,
It took longer than measuring other characteristics and parameters of the transistor.

It is an object of the present invention to provide a transistor characteristic measuring circuit which determines the value of this parameter n of a transistor and realizes it simply and at high speed by reading the output only once.

[Means for solving problems]

The transistor characteristic measuring circuit of the present invention comprises an AC voltage source having a frequency ω and a first DC voltage source connected in series between the emitter terminal and the base terminal of a transistor under measurement whose emitter terminal is grounded, and the transistor under measurement. An operational amplifier whose collector terminal is connected to the inverting input terminal, a diode whose cathode is connected to the inverting input terminal of this operational amplifier, and whose anode is connected to the output terminal of the operational amplifier; and a non-inverting input terminal of the operational amplifier. A second DC voltage source connected between the emitter terminals, an output terminal and a non-inverting input terminal of the operational amplifier are connected to a measurement signal input terminal, and an output voltage of the AC voltage source is supplied to a reference signal input terminal. And a reading means for reading the output of the lock-in amplifier.

[Action]

According to the present invention, the transistor to be measured is used with the emitter grounded, and a predetermined direct current bias and an alternating voltage with a frequency ω are applied between the emitter terminal and the base terminal by the first direct current voltage source and the alternating current voltage source, respectively. The base-emitter voltage V _BE is defined by this. The operational amplifier keeps the voltage of the collector terminal of the transistor through the diode so as to be the voltage of the non-inverting input terminal (collector-base voltage) defined by the second DC voltage source, and all the collector current I _{c of the} transistor is It will pass through the diode.

The direct current bias is V ₀ , the output voltage of the AC voltage source is represented by a · cos (ωt), and the collector current of the transistor is represented by I _c = I ₀ · exp (eV _BE / nkT). Regarding the diode, if the applied voltage is V _f and the n value is n ′, and its current I _f is represented by I _f = I ₀ ′ · exp (eV _f / n′kT), the collector current I _c and the diode Of I
Assuming that _f is equal, I ₀ · exp (eV _BE / nkT) = I ₀ ′ × exp (eV _f / n′k
T). If the logarithm of both sides is taken, log (I _o ) + eV _BE / nkT = log (I ₀ ′) + eV _f / n′k
T becomes, and V _f = (n ′ / n) · V _BE + (n′kT / e) log (I ₀ / I ₀ ′).

Since V _BE is set to V _o + a · cos (ωt), V _f = (n ′ / n) · a · cos (ωt) + (n ′ / n)
It becomes V _o + (n′kT / e) log (I ₀ / I ₀ ′).

The potential difference between the collector terminal and the output terminal of the operational amplifier is V _f , but as a result, an AC voltage component of amplitude (n ′ / n) a at frequency ω is also generated between these terminals. This is input to the measurement signal input terminal of the lock-in amplifier.
On the other hand, the output voltage of the frequency ω of the AC voltage source is input to the reference signal input terminal of the lock-in amplifier.

As a result, in the lock-in amplifier, the frequency ω of the reference signal is
Since the measurement signal is chopped at, only the input measurement signal having the frequency ω is amplified, further converted into direct current, and output. If the gain of the lock-in amplifier is β, its output is β (n ′ / n) a. By reading this, since β, n ′, and a are all known, the value of n of the transistor to be measured can be directly known from this output.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. As shown in FIG. 1, the circuit of this embodiment includes an AC voltage source 10 having a frequency ω, a first DC voltage source 12, an operational amplifier 20, a diode 21, and a second DC voltage source.
, A DC voltage source 22, a lock-in amplifier 30, and a voltmeter 70.

The AC voltage source 10 and the first DC voltage source 12 are connected in series, and these are a DC bias V ₀ between the base and emitter of the transistor under measurement and an AC voltage a · co of frequency ω.
A voltage source that gives s (ωt) is constructed. Between the inverting input terminal and the output terminal 4 of the operational amplifier 20, a diode 21 is connected with a polarity connecting the cathode side to the inverting input terminal and the anode side to the output terminal 4, and the non-inverting diode of the operational amplifier 20 is connected. A second DC voltage source 22 is connected between the inverting input terminal 5 and one end of the AC voltage source 10.

Transistor 11 that is a measured bipolar transistor
Are connected as follows in measurement. That is, the emitter terminal 1 of the transistor 11 is grounded and connected to the AC voltage source 10 and the second DC voltage source 22, the base terminal 2 is connected to the first DC voltage source 12, and the collector terminal is further connected. 3 is connected to the inverting input terminal of the operational amplifier 20 and the cathode of the diode 21.

The output terminal 4 and the non-inverting input terminal 5 of the operational amplifier 20 are connected to the measurement signal input terminal 31 of the lock-in amplifier 30, and both ends of the AC voltage source 10 are connected to the reference signal input terminal 32 of the lock-in amplifier 30. This lock-in amplifier has been
A voltmeter 70 is connected to the output terminal of 30.

The diode 21 described above has a known characteristic.

Thus, the transistor characteristic measuring circuit of the present embodiment is
Ground the emitter terminal 1 of the transistor 11 to be measured,
An AC voltage source 10 having a frequency ω and a DC voltage source 12 having a DC bias V ₀ are connected in series between the emitter terminal 1 and the base terminal 2, and the collector terminal 3 is connected to the inverting input terminal of the operational amplifier 20 and the cathode of the diode 21. Connected to the operational amplifier 20
Is connected to the anode of the diode 21, the DC voltage source 22 is connected between the non-inverting input terminal 5 of the operational amplifier 20 and the emitter terminal 1, and the set of terminals 4 and 5 is connected to the lock-in amplifier 30. The measurement signal input terminal 31 is connected, the output voltage of the AC voltage source 10 is connected to the reference signal input terminal 32 of the lock-in amplifier 30, and the voltmeter 70 is connected to the output terminal of the lock-in amplifier 30. As shown in FIG. 2, the lock-in amplifier 30 includes an operational amplifier 60 for a measurement input signal, a phase shift circuit 62, a waveform shaping circuit 64 using a comparator, a phase discrimination detector 66 using a FET, and a low-pass filter 68. It consists of.
The output of the lock-in amplifier 30 is read by the voltmeter 70.

Next, the operation of this embodiment will be described.

The transistor 11 to be measured is used with its emitter grounded as described above. First DC voltage source 12 and AC voltage source 10
Is a voltage source that applies a DC bias V ₀ and an AC voltage a · cos (ωt) of frequency ω between the emitter terminal 1 and the base terminal 2 of the transistor 11, respectively, and defines the base-emitter voltage V _BE . The operational amplifier 20 is a diode
Through 21 the voltage at the collector terminal 3 of the transistor 11 is maintained at the voltage at the non-inverting input terminal 5 (collector-base voltage) defined by the second voltage source 22. Further and thus through all the collector current I _c of the transistor 11 diode 21. The collector current of the transistor 11 is expressed as I _c = I ₀ · exp (eV _BE / nkT) as in the above-mentioned equation (1), and the applied voltage for the diode 21 is V _f and the n value is n ′. its current _{I f} is _{I f = I 0 '· exp} (eV f / n'kT) ... (3) and to equal the current _{I f} of the collector current _{I c} and the diode 21 if expressed I ₀ · exp (EV _BE / nkT) = I ₀ ′ · exp (eV _f / n′kT) (4) If the logarithm of both sides of the equation (4) is taken, log (I _o ) + eV _BE / nkT = log (I ₀ ′) + eV _f / n′kT (5) and V _f = (n ′ / n) · V _BE + (n′kT / e) log (I ₀ / I ₀ ′) (6)

Here, since V _BE is set to V _o + a · cos (ωt) by the AC voltage source 10 and the first DC voltage source 12, if this is substituted into the equation (6), V _f = (n ′ / N) ・ a ・ cos (ωt) + (n '/ n)
V _o + (n′kT / e) log (I ₀ / I ₀ ′) (7)

The potential difference between the collector terminal 3 and the output terminal 4 is V _f ,
As a result, the amplitude (n '/ n) is generated at the frequency ω between these terminals.
An AC voltage component of a will also be generated. This is input to the measurement signal input terminal 31 of the lock-in amplifier 30. On the other hand, the AC voltage source 10 is connected to the reference signal input terminal 32 of the lock-in amplifier.
The output voltage of frequency ω is input.

As a result, in the lock-in amplifier 30, since the measurement signal is chopped at the frequency ω of the reference signal, only the input measurement signal having the frequency ω is amplified and further converted into direct current and output. Become. That is, in the case of the lock-in amplifier 30 having the configuration shown in FIG. 2, the output of the AC voltage source 10 applied to the reference signal input terminal 32 is a sine wave having a frequency ω. By passing through the waveform shaping circuit 64, a rectangular wave of frequency ω is obtained. On the other hand, the measurement signal input is equal to the voltage applied to the diode 21 of known characteristics, which is received by the differential amplifier 60, then sent to the phase discrimination detector 66, and driven by the rectangular wave of the frequency ω. It is chopped by FET and converted to direct current by low pass filter 68. Since all the components other than the frequency ω are removed by the phase discrimination detector 66, the output of the lock-in amplifier 30 eventually appears in proportion to the amplitude of the component of the frequency ω in the voltage V _f applied to the diode 21. Becomes

In this way, the measured signal corresponding to the component of the frequency ω in the above equation (7) is output from the lock-in amplifier 30, and the gain of the lock-in amplifier 30 is β.
Then, the output voltage is β (n ′ / n) a. If this is read by the voltmeter 70, β, n ′, and a are all known, so that the value of n of the transistor 11 to be measured can be directly known.

In this way, the value of n of the transistor 11 to be measured can be determined by reading the output of the lock-in amplifier 30 only once with the voltmeter 70.

The time required to determine the parameter n is mostly read by the voltmeter 70, and is about several hundred milliseconds when read by the control computer.

〔The invention's effect〕

As described above, according to the present invention, it is not necessary to set the voltage or read the current a plurality of times, and the value of n can be determined by reading the output once. Therefore, the voltage-current characteristic of the bipolar transistor can be determined. The parameter n can be measured simply and quickly, and is extremely useful in practice in the case of measuring and evaluating a large number of transistors on a wafer.

[Brief description of drawings]

1 is a circuit diagram for explaining a voltage-current characteristic measuring circuit of a transistor according to an embodiment of the present invention, FIG. 2 is a circuit diagram including a concrete configuration of the lock-in amplifier of FIG. 1, FIG. 3 is a circuit diagram for explaining a conventional measuring circuit, and FIG. 4 is an explanatory diagram of a conventional method of obtaining a parameter n using the measuring circuit of FIG. 1 …… Emitter terminal 2 …… Base terminal 3 …… Collector terminal 4 …… Output terminal 5 …… Non-inverting input terminal 10 …… AC voltage source 11 …… Measured transistor 12 …… First DC voltage source 20 ...... Operational amplifier 21 …… Diode of known characteristics 22 …… Second DC voltage source 30 …… Lock-in amplifier 31 …… Measurement signal input terminal 32 …… Reference signal input terminals 41, 42 …… DC voltage source 43… ... Ammeter 45 ... Operational amplifier 60 ... Differential amplifier 62 ... Phase shift circuit 64 ... Waveform shaping circuit 66 ... Phase discrimination detector 68 ... Low-pass filter 70 ... Voltmeter

Claims (2)

[Claims] 1. An AC voltage source and a first DC voltage source having a frequency ω, which are connected in series between an emitter terminal and a base terminal of a transistor under measurement whose emitter terminal is grounded, and a collector terminal of the transistor under measurement. An operational amplifier connected to the inverting input terminal, a diode having a cathode connected to the inverting input terminal of the operational amplifier and an anode connected to the output terminal of the operational amplifier, and a non-inverting input terminal of the operational amplifier and the emitter terminal. A lock-in in which a second DC voltage source connected in between, an output terminal and a non-inverting input terminal of the operational amplifier are connected to a measurement signal input terminal, and an output voltage of the AC voltage source is supplied to a reference signal input terminal. A transistor characteristic measuring circuit comprising an amplifier and a reading means for reading the output of the lock-in amplifier. 2. The transistor characteristic measuring circuit according to claim 1, wherein a voltmeter connected to an output terminal of a lock-in amplifier is used as the reading means.