JPS6347065Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a differential amplifier circuit suitable for semiconductor integrated circuits.

Differential amplifier circuits are widely used as amplifiers for integrated circuits because they have suitable characteristics.
Since the noise characteristics and gain characteristics of an amplifier largely depend on the characteristics of the first stage transistor, it is important to test the operation of the first stage transistor in the manufacturing test of this type of integrated circuit.

FIG. 1 shows a power amplifier circuit having a differential amplifier circuit at the input stage and a pushable amplifier circuit at the output stage. The input stage differential amplifier circuit has a pair of transistors Q ₁ and Q ₂ , and their current source is composed of a transistor Q ₃ , diodes D ₁ and D ₂ and a resistor R ₂ . Resistors R ₃ and R ₄ are connected in series between power supplies to form a bias voltage generation circuit, and the voltage is supplied to the base of transistor Q ₁ via resistor R ₁ . The base of the transistor Q ₁ is supplied with an input signal via the input terminal T ₁ . A terminal _T3 is provided at the connection point between the resistors _R3 and _R4 , and a ripple filter capacitor _C1 for suppressing power supply ripple is connected to this. The output stage is a well-known pushable circuit and has no direct relation to the present invention, so a description thereof will be omitted.

As mentioned above, since the characteristics of the amplifier circuit greatly depend on the characteristics of the first stage transistor, it is necessary to perform an operation test on the transistors Q ₁ and Q ₂ that constitute the input stage differential amplifier. For this purpose, it is sufficient to measure the current flowing through the transistors Q ₁ and Q ₂ . Conventionally, the common method for measurement is to check the emitter current of transistor _Q3 by measuring the voltage across resistor _R2 . transistor
The base-emitter voltage V _BE of Q ₃ is diode D ₁
is approximately equal to the voltage drop V _F1 across the resistor R 2, so the voltage across the resistor R ₂ is equal to the voltage drop V _F2 across the diode D ₂ . Therefore, the emitter current (collector current) I ₀ of the transistor Q ₃ becomes I ₀ =V _F2 /R ₂ .

However, integrated circuits have a resistance value deviation of about 15%, which makes it impossible to accurately measure current values. At the same time, the deviation of resistor R ₂ has a large effect on the bias current of transistor Q ₃ , making it impossible to sufficiently test the operation of the first stage transistor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a differential amplifier circuit having a configuration in which the current flowing through the transistors constituting the differential amplifier circuit can be measured without being affected by variations in the absolute value of the current source resistance.

In the present invention, two resistors are connected in series between the base of one of a pair of transistors connected in a differential type and the output terminal of a bias voltage generation circuit, and the resistors are close to the base of one of the transistors. The resistor on the far side has a sufficiently high resistance value to provide the necessary input impedance, and the resistor on the far side has a resistance value proportional to the resistance value of the current source resistor.

With this configuration, it is possible to measure the current flowing through the transistor depending on the resistance ratio, regardless of the absolute value of the resistance value. In integrated circuits, variations in resistance ratio can be suppressed to a fairly small level, so that accurate operation tests of transistors can be performed. Furthermore, the two resistors determine the input impedance, and since the resistor closer to the base of the transistor has a sufficiently high resistance value, a drop in the input impedance is also prevented.

The present invention will be described below with reference to drawings.

FIG. 2 is a circuit diagram showing one embodiment of the present invention.
FIG. 2 is a diagram showing only the portions corresponding to the portions indicated by dotted lines in FIG. 1. Terminals T ₁ and T ₂ are differential input terminals of the amplifier circuit, each connected to transistor Q ₁
and connected to the base of Q ₂ . The emitters of transistors Q ₁ and Q ₂ are connected in common,
Coupled to the collector of transistor _Q3 .
Biasing diodes D ₁ and D ₂ are connected in series to the base of the transistor Q ₃ , and their emitters are connected to a common potential point via a resistor R ₂ .
In such a differential amplifier circuit, the transistor
The feature of this invention lies in the base bias circuit of _Q1 . That is, the base of transistor Q ₁ and
Two resistors _R11 and _R12 are connected in series to the connection point between the bias voltage generating bleeder resistors _R3 and _R4 . A terminal _T3 is provided at the connection point between the resistors _R11 and _R12 .

Comparing this with the conventional example shown in Figure 1, the resistor R ₁ in the conventional circuit is divided into two series resistors R ₁₁ and R ₁₂ in the present invention, and the terminal T ₃ is provided at this connection point. I can understand that it is something that

Terminal T ₃ is often connected to an external large-capacity capacitor C ₁ to suppress power supply ripples, etc., and resistor R ₁₁ serves as an input load resistance, so it must have a high resistance (for example, 20 kΩ or more). It is composed of Resistor R ₁₂ is configured with the same diffusion pattern to have the same value as resistor R ₂ . That is,
This property is utilized because two resistors designed in close proximity on an integrated circuit under the same conditions can easily be manufactured equally.

Operational measurements are performed by applying the power supply voltage to the circuit and applying the resistor
Measure the voltage across _R12 . This measurement is made using a resistor
The voltage across R ₁₂ may be measured directly, but first a high voltage input is applied to terminal T ₂ , and the collector current I ₀ of transistor Q _{3 is} measured directly.
If absorbed on the side, the base current of transistor Q ₁ disappears, so the voltage at terminal T ₃ is reduced by resistors R ₃ and R ₄
is equal to the connection point of Next, when the voltage at terminal T ₂ is set to a low value, the base current of transistor Q ₁ flows, and the voltage at terminal T ₃ at this time is measured,
Determining the difference from the voltage at the first terminal _T3 is equivalent to measuring the voltage V _R12 across resistor _R12 .

Next, to explain the obtained voltage V _R12 , in FIG. 2, the bias diodes D ₁ and D ₂
As mentioned above, the relationship between the forward potentials V _F1 and V _F2 of the transistor Q3 and _the base-emitter voltage V _BE of the differential input transistor is determined from the manufacturing conditions of the semiconductor, such that V _BE ≒ V _F1 . The current is I ₀ =VF ₂ /R ₂ . If the current amplification factor of the transistor Q ₁ is h _FE and a potential lower than the voltage of the terminal T ₁ is applied to the base of the transistor Q ₂ , that is, the terminal T ₂ , the transistor Q ₂ will be cut off, so the current I ₀ will be the same as that of the transistor Q ₁ The emitter current is , and its base current I _BQ1 is I _BQ1 = I ₀ /h _FE = V _F2 / _R2 × h _FE . The voltage drop of this base current across resistor R ₁₂ is V _R12 = I _BQ1 × R ₁₂ = V _F2 × R ₁₂ /R ₂ × h _FE . Here, the feature of the present invention is that if the designed conditions are substituted for R ₁₂ = R ₂ , V _R12 = V _F2 /h _FE , that is, h _FE = V _F2 / h _R12 , and the current amplification factor h _FE can be To find this, it is sufficient to measure the voltage drop that occurs across the resistor _R12 . Moreover, as can be seen from this method, the measurement results are not affected by the resistance value.

From the above explanation, providing terminal T ₃ at the connection point of resistors R ₁₁ and R ₁₂ facilitates voltage measurement.
It is advantageous in that it can be coupled with the capacitor C ₁ , but in the present invention it is important to connect the two resistors R ₁₁ and R ₁₂ between the base of the transistor Q ₁ and the connection point of the resistors R ₃ and R ₄ . be. That is, the above-described measurement method of the present invention can be applied to the circuit shown in FIG. 1, and if R ₁ =R ₂ at that time, h _FE of transistor Q ₁ is expressed by V _F2 /V _R1 . However, since the resistor R ₁ serves as a bias supply path to the transistor Q ₁ and determines the input impedance, a very high resistance value is required. On the other hand, since the resistor R ₂ is a current source resistor and determines the current flowing through the transistors Q ₁ and Q ₂ , its resistance value is determined according to the characteristics of the differential amplifier. Therefore, it is impossible to set R ₁ =R ₂ , and R ₁ =KR ₂ (K is a proportionality constant). The variation in the resistance ratio in integrated circuits is quite small compared to the absolute value of the resistance value, but since a high resistance value is required as the resistor _R1 , the variation in the resistance ratio with the resistor _R2 becomes large. As a result, the operating characteristics of transistor _Q1 cannot be sufficiently tested.

This problem arises when there are two resistors as shown in Figure 2.
This can be solved by providing R ₁₁ and R ₁₂ . That is, it is possible to provide the resistor R ₁₁ with a sufficiently high resistance value to achieve the required input impedance. resistor input impedance
Since R ₁₁ is almost determined, it is possible to select the resistance value of resistor R ₁₂ , and it is possible to select the resistance value of R ₁₂ , and it is possible to set R ₁₂ = R ₂ ,
The variation in both resistance ratios becomes extremely small. Therefore, the h _FE of the transistor Q ₁ is not affected by the absolute value of the resistance, but the voltage drop across the resistor R ₁₂ and the diode
D is precisely measured by the voltage drop of ₂ .

FIG. 3 shows another embodiment of the present invention, in which the emitters of transistors Q ₁ and Q ₂ constituting a differential amplifier are directly coupled to a resistor R ₃ , so that transistors Q ₃ and
The circuit differs from the one in Figure 2 because the diodes D ₁ and D ₂ have been removed. In this case as well, if the resistors R ₂ and R ₁₂ are configured so that R ₂ =R ₁₂ , the voltage across the resistor R ₁₂ can have a value proportional to the current amplification factor h _FE .

As described above, according to the present invention, the operating state of the first stage of the integrated circuit amplifier can be determined appropriately by simply measuring the voltage between the terminals of the resistor that is farther from the base of the transistor among the two newly installed resistors. A circuit that can be tested is obtained. Furthermore, variations in characteristics such as a decrease in input impedance due to circuit changes may occur.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, and FIGS. 2 and 3 are circuit diagrams showing embodiments of the present invention. Q ₁ , Q ₂ , Q ₃ ...transistor, R ₁ , R ₂ , R ₃ ,
R ₄ , R ₁₁ , R ₁₂ ... Resistor, D ₁ , D ₂ ... Diode,
C ₁ ... Filter capacitor, T ₁ , T ₂ , T ₃ ...
terminal.

Claims (1)

[Scope of utility model registration request] first and second transistors connected in a differential manner; a current source forming at least a part of a current source circuit for the first and second transistors and determining the current of the current source circuit; and a voltage generation circuit that generates a bias voltage to the base of the first transistor, the differential amplifier circuit includes a voltage generation circuit that generates a bias voltage to the base of the first transistor. two resistors are connected in series, and of the two resistors, the resistor closer to the base of the first transistor has a resistance value that provides a necessary input impedance, and the resistor that is closer to the base of the first transistor A differential amplifier circuit characterized in that a resistor located far from the current source has a low resistance value that is proportional to the resistance value of the current source resistor.