JPH0821831B2 - Integrator circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an integrating circuit which is a constituent element of an active filter, and more particularly to an integrating circuit which is a constituent element of a filter suitable for being integrated into an IC.

[Conventional technology]

When making a circuit including a filter into an IC, how to incorporate the filter inside the IC and reduce the external parts becomes an important issue. In general, an active filter is used when the filter is integrated into an IC. (1) The accuracy of the resistance value and the capacitance value of the capacitor is not good, and the cutoff frequency determined by the product of them varies.

(2) Since the resistance value and the capacitance value of the capacitor cannot be increased so much, it is difficult to make one with a low cutoff frequency.

There are problems such as.

Devices related to this kind of device for solving the above-mentioned problems are disclosed in, for example, Japanese Patent Laid-Open Nos. 55-45224 and 55-55.
-45266 publication etc. are mentioned.

[Problems to be solved by the invention]

The above-mentioned prior art does not consider the high frequency performance of the transistor, and has a problem in using it in a circuit that needs to process a high-bandwidth signal.

Generally, the transition frequency _T, which is an index showing the high frequency performance of a transistor, changes as shown in FIG. 2 depending on the emitter current. In order to improve the high frequency performance, the emitter current should be increased and used in a region where _T can be increased.

In this case, as will be described later, the capacitance value of the capacitor becomes large and the chip area increases when it is made into an IC.

An object of the present invention is to eliminate the above-mentioned problems and provide an integration circuit suitable for an IC filter.

[Means for solving problems]

The present invention has an amplifier for converting a signal voltage into a current and a load capacitor, divides the signal voltage and supplies it to the amplifier.

In the present invention, two resistors for dividing the input signal are connected to the input transistor, and means for controlling the current value of the power supply for supplying the emitter current of the differential amplifier is provided.

[Action]

The present invention comprises an amplifier for converting a signal voltage into a current and a load capacitor, which divides the signal voltage and connects it to the amplifier. The integral gain of the integrator circuit is gm / a · 1 / c where the transconductance gm of the amplifier and the capacitance value C of the load capacitor are 1 / a and the voltage division ratio of the input signal voltage is 1 / a. Therefore, when designing a predetermined time constant, the capacitance value can be designed to be smaller by C / a. Therefore, it is suitable for IC.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to FIG.

In FIG. ₁ , the emitter of the transistor Q _{1 and} the emitter of the transistor Q ₂ are connected to each other, and the emitter is connected to the variable current source A ₁ so that the transistors Q ₁ and Q _{2 form} a differential pair. . Also, the base of transistor Q ₁ is a resistor
The input signal voltage v _in is applied to the input terminal T ₁ via R ₁ and the bias voltage V _B1 is applied to the base of the transistor Q _2.
Is added.

The collector of the transistor Q ₂ is connected to the variable current source A ₂ and the other end of the transistor Q ₂ is connected to the load capacitor C, and the output signal voltage is obtained from the output terminal T ₃ . The variable current sources A ₁ and A ₂ are controlled by the signal of the control terminal T ₂ , and when the current value of the current source A ₁ is I ₀ , the current value of the current source A ₂ is I _o.
It is controlled by maintaining a relationship such that / 2.

In such a configuration, the input voltage of the terminal 1 is v _in , the output voltage of the terminal T ₃ is v _out , and the transistor Q
_The AC current flowing through the collector of ₂ is i _s , the transistor Q ₁ , Q ₂
As each emitter resistance of the r _e, And the current i _s flows through the capacitor C,
Obtain the output voltage v _out . If the angular frequency of the signal is ω, S: It becomes Laplace operator, and the transfer function H of this circuit from Eqs. (1) and (2)
_{When 1} (S) is calculated, And the gain is It is shown that it is an integrating circuit represented by. The emitter resistance r _e is determined by the emitter current I _E. k: Boltzmann constant T: absolute temperature q: is represented by the electron charge, r _e = 2 in the emitter current 100μA at room temperature
It is 60Ω.

Generally, the transition frequency _T indicating the high frequency performance of a transistor changes as shown in FIG. 2 depending on the emitter current I _E. Therefore, in order to improve the high frequency performance, the emitter current should be increased and used in a region where the frequency _T can be large.

If the integral gain is determined by the emitter resistance r _e , there is a case where the high frequency performance is not improved and the performance cannot be obtained because it does not match the condition for using the transistor. Therefore, in the present invention, the input signal is attenuated by the voltage divider by the resistors R ₁ and R ₂ and input to the differential pair, and the resistance value that substantially determines the time constant is expressed by the equation (4) with respect to the emitter resistance. hand Set to double. Therefore, the transistors Q ₁ and Q ₂ can always be operated with an emitter current having a large frequency _T.

In addition, the capacitor capacity C and the current source
When the current values of A ₁ and A ₂ vary and the integral gain changes, by controlling the control voltage V _C of the control terminal T ₂ , the emitter currents of the differential pair Q ₁ and Q ₂ are changed, A desired integral gain can be obtained. Further, the resistors R _1, R _2, terminals T ₁
Since the signal voltage input to is divided and applied to the differential pair Q ₁ and Q ₂ , the actual input dynamic range can be expanded,
Distortion and noise characteristics can be improved.

FIG. 3 shows another embodiment of the present invention. In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals. FIG. 3 is different from FIG. 1 in that the variable current source A ₂ is connected to the collector of a diode-connected transistor Q ₄ with respect to the PNP transistor pair Q ₃ and Q ₄ that operates as a current mirror, and the other is connected. That is, the collector of the transistor Q ₃ is connected to the collector of the transistor Q ₂ . In this configuration, by setting the current value of the current source A ₁ to I ₀ and the current value of the current source A ₂ to I _0/2 , the same operation as in FIG. 1 is performed.

FIG. 4 shows another embodiment of the present invention. 4, the same components as those in FIG. 1 are designated by the same reference numerals. The difference between FIG. 4 and FIG. 1 is that the collector of the transistor Q ₂ is connected to the collector of the transistor Q ₄ of one of the PNP transistor pair Q ₃ and Q _{4 that} operates in the current mirror, and the collector of the transistor Q ₁ is It is connected to the other diode-connected transistor Q ₁ . In this configuration, the current source
If the current value of A ₁ and I _0, the transistors Q ₁ and the collector current of Q ₂ are direct-current operation are each I _0/2 is the same as Figure 1.

On the other hand, the signal current flowing through the load capacitor becomes i _s1 + i _s2 by the transistors Q ₃ and Q ₄ operating in the current mirror, and the integral gain is Is represented by Therefore, the integral gain is double that of FIG.

FIG. 5 shows another embodiment of the present invention. In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals. The transistor Q ₅ and the constant current source A _{3 form} an emitter follower. The integrated output of the capacitor C is applied to the base of the transistor Q ₅ and taken _out from the emitter via the terminal T ₄ as the output voltage v _out . On the other hand, it is also added to the base of the transistor Q ₂ via the transistor Q ₅ to form a negative feedback loop.

Therefore, the transfer function H ₂ (S) of FIG. And the cutoff frequency W _C becomes Is a low-pass filter.

In this case, the variation of the capacitor C can be used to adjust the r _e by varying the emitter current of the transistor Q _1, Q _2, it can be accurately set. The capacitor C, and even if the value of the emitter resistance r _e is small by the resistance R ₁ and R ₂ Since the cutoff frequency W _C can be lowered by increasing the value of, the capacitor C can be integrated in the IC even with a filter having a low cutoff frequency, so that the effect of IC integration is great.

FIG. 6 shows still another embodiment in which the integrating circuit of the present invention is a high pass filter. In Fig. 1, Fig. 1,
The same components as those in FIG. 5 are designated by the same reference numerals. Input voltage
v _in has a load capacitor C added through terminal T ₅ . The other end of the capacitor C is connected to the collector of the transistor Q ₂ . The base of transistor Q ₁ is bias voltage V _B3
It is connected to the. Therefore, the transfer function H of FIG.
₃ (S) is , Which represents a high-pass filter. It is obvious that the same effect as the embodiment of FIG. 5 can be obtained.

A more general application of the integrating circuit is a biquad filter shown in FIG. In FIG. 7, G ₁ and G ₂ are integrator circuits, and the integral gains are G ₁ and G ₂ , respectively. Also G ₃ ,
G _4, G ₅ is a constant c for determining the magnitude of the input voltage v _in each, b,
The coefficient circuit which gives a is shown. The input voltage v _in is applied to terminal T ₆ and the output voltage v _out is represented at terminal T ₇ . The transfer function H ₄ (S) of the circuit in FIG. 5 is , And various filters for low pass, high pass, band pass, etc. can be configured by the values of a, b, and c.

The coefficients a, b and c in FIG. 7 are shown in FIG. 8 as a = 0, b, respectively.
An embodiment of the present invention that constitutes a low-pass filter with = 0 and c = 1 will be described. In FIG. 8, the transistors in the circuit corresponding to the integrating circuit G ₁ in FIG. 7 are numbered 100, the transistors corresponding to G ₂ are numbered 200, and the two-digit number is the transistor pair 101, 102 and 201, 202. 3 shows an emitter current control circuit. here Selected for the transistors Q ₁₀₂ and Q ₁₀₃ , and Q ₂₀₃ and Q.
The collector currents of ₂₀₂ are equal.

Therefore, the transfer function H ₅ (S) of the circuit of FIG. And shows a second-order low-pass characteristic.

Where R ₁₀₁ = R ₁₀₄ R ₁₀₂ = R ₁₀₃ , R ₂₀₁ = R ₂₀₄ R ₂₀₂ = R
_{It was set to 203} . It is obvious that the effect of the present invention is the same as that of the other embodiments in the embodiment of FIG.

FIG. 9 shows another embodiment of the present invention. 9, the same components as those in FIG. 8 are designated by the same reference numerals. Figure 9 is number 8
FIG differs, the collector of the transistor Q ₁₀₂ is connected to the collector of Q _106, the collector of the emitter and Q ₁₀₃ of Q ₁₀₆ is connected, and the collector of the transistor 202 is connected to the collector of Q ₂₀₆ , With Q ₂₀₆ collector
This means that the collector of Q ₁₀₃ is connected. The bases of transistors Q ₁₀₆ and Q ₂₀₇ are connected to bias voltage V _B10 . The effects of the transistors Q ₁₀₆ and Q ₁₀₇ are C ₁₀₁ and C _201.
This is provided in order to increase the drive impedance of, and the substantial operation is the same as in FIG.

〔The invention's effect〕

According to the present invention, it is possible to operate a transistor with an emitter current in an operating region having the most excellent high frequency characteristics and to select an integral gain to an arbitrary value. Therefore, even when the filter is made into an IC, high frequency characteristics are excellent, and even a filter having a cutoff at a low frequency can be configured with a small capacitance, which is effective in making the IC.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing high frequency characteristics of a transistor, FIG. 3, FIG.
5 and 6 are circuit diagrams showing another embodiment, FIG. 7 is a block diagram showing a general biquadratic filter, FIG. 8 and FIG.
The drawing is a circuit diagram showing still another embodiment. T ₁ ...... Input terminal, T ₂ ...... Control terminal, T ₃ ...... Output terminal, R ₁ , R ₂ ...... Resistor for voltage division.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Kamiya 471 Kamono-cho, Minokamo City, Gifu Prefecture Gifu Factory, Hitachi Ltd. (56) References JP-A-55-45224 (JP, A) JP-A-SHO 55-45266 (JP, A)

Claims (2)

[Claims] 1. A first and second transistor forming a differential pair, a first current source for supplying an emitter current of the first and second differential pair transistors, and the first current source. Means for controlling the current value of the second transistor, a load capacitor connected to the collector of the second transistor and a second current source, a voltage dividing means for the input signal voltage, and an output of the voltage dividing means for the first voltage.
And a voltage source for supplying a bias voltage to the base of the second transistor, wherein the voltage dividing means is connected in series between the signal input terminal and the first transistor. A first resistor and a second resistor connected to the first transistor and an AC ground potential. The voltage dividing means divides the first and second transistors into an operating region excellent in high frequency characteristics. An integrating circuit characterized by being operated by an emitter current and being capable of selecting an integral gain to an arbitrary value. 2. A first and second transistor forming a differential pair, a first current source for supplying an emitter current of the first and second differential pair transistors, and the first current source. Means for controlling the current value of the second transistor, a load capacitor connected to the collector of the second transistor and a second current source, a voltage dividing means for the input signal voltage, and an output of the voltage dividing means for the first voltage.
Means for supplying the base of the second transistor to the base of the second transistor, and means for negatively feeding back the integrated output extracted from the connection point of the collector of the second transistor and the load capacitor to the base of the second transistor. The means comprises a first resistor connected in series between a signal input terminal and the first transistor, and a second resistor connected to the first transistor and an AC ground potential, and the voltage dividing ratio of the voltage dividing means. According to the integration circuit, the first and second transistors can be operated with an emitter current in an operating region having excellent high frequency characteristics and an integral gain can be selected to an arbitrary value.