JPH0795665B2 - Integrator circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrating circuit suitable for application to, for example, a multipurpose filter.

[0002]

2. Description of the Related Art A multipurpose filter shown in FIG. 1 is provided. In FIG. 1, 1 indicates an input terminal and 2 indicates an output terminal. The input terminal 1 is connected to the inverting input terminal of the first stage operational amplifier 4 via the resistor 3. This operational amplifier 4 forms an integrating circuit, and the characteristic of itself is determined by a resistor 5 and a capacitor 6 which form a feedback resistance. The output terminal of the operational amplifier 4 is connected to the inverting input terminal of the operational amplifier 8 of the next stage via the resistor 7. This operational amplifier 8 also forms an integrating circuit, and the characteristic of itself is determined by the resistor 7 and the capacitor 9 which form the input resistance. The output of the operational amplifier 8 is amplified by the inverting amplifier 10 and then fed back to the inverting input terminal of the operational amplifier 4 in the first stage via the resistor 11. The inverting amplifier 10 is composed of an operational amplifier 12.

In this case, a bandpass output is obtained from the output terminal of the operational amplifier 4, and a lowpass output is obtained from the output terminal of the operational amplifier 12.

The operational amplifier 13 forms an adder, and the inverting input terminal (input terminal of the adder) of the operational amplifier 13 can be supplied with the bandpass output and the lowpass output. The input signal from the input terminal 1 can also be supplied to the inverting input terminal.

If only the output signal of the operational amplifier 4, that is, the bandpass output is supplied to the operational amplifier 13, the bandpass output can be obtained at the output terminal 2. If only the output signal of the operational amplifier 12, that is, the low-pass output is supplied to the operational amplifier 13, the low-pass output can be obtained at the output terminal 2.

If both the input signal and the bandpass output are supplied to the operational amplifier 13, the phases of both signals are opposite to each other, so that a trap output can be obtained at the output terminal 2. If both the input signal and the low-pass output are supplied to the operational amplifier 13, a high-pass output is similarly obtained at the output terminal 2.

[0007]

By the way, such a multipurpose filter requires four high gain operational amplifiers. That is, the operational amplifiers 4, 8, 12, and 13.
Then, it is necessary to discretely connect these operational amplifiers 4, 8, 12, and 13 with resistors and capacitors.
Therefore, the structure becomes complicated. The characteristic of the multipurpose filter is determined by the characteristic of the integrating circuit formed by the operational amplifiers 4 and 8 and the value of the feedback resistor 11. Specifically, it is determined by the constants of the resistors 5, 7, 11 and the capacitors 6, 9. If the temperature coefficient of these constants is large, the filter has a temperature characteristic that cannot be ignored. Therefore, resistors 5, 7, 11 and capacitors 6, 9 having a small temperature coefficient, that is, expensive ones are required.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide an integrating circuit having a simple structure and having a small temperature dependence of the transfer characteristic.

[0009]

According to the integrating circuit of the present invention, the first differential amplifier is formed by connecting the first constant current source to the emitters of the first and second transistors commonly connected. A pair of diode loads are connected, an input signal is supplied to the base of the first transistor, a reference voltage is applied to the base of the second transistor, and the commonly connected third and third transistors are connected.
A logarithmically converted voltage obtained across the pair of diode loads is supplied to a second differential amplifier in which the emitter of the fourth transistor is connected to the second constant current source, and the second difference is supplied. One of a pair of outputs of the dynamic amplifier is supplied to a capacitor via a current mirror circuit, and a third constant current source having a current value 1/2 of the value of the second constant current source is connected in parallel to the capacitor. The integrated circuit is configured by an integrated circuit, and the gain is controlled by controlling the current ratio of the first and second constant current sources by a resistor externally attached to the integrated circuit.

[0010]

According to the integrating circuit of the present invention, the first differential amplifier Q is formed by connecting the first constant current source to the commonly connected emitters.
₁ and Q ₂ are connected to diode loads Q ₃ and Q ₄ , the logarithmically converted voltage obtained at both ends of the diode loads Q ₃ and Q ₄ is connected, and a common constant emitter is connected to a second constant current source. To the second differential amplifiers Q ₅ and Q ₆
Of the differential amplifiers Q ₅ and Q ₆ of the current mirror circuit 3
7, since the through Q ₇ and then supplied to the capacitor 36, there is a dynamic range, it can be increased advantages of the signal component of the output. In addition, a current ratio (I ₁ / I 2) of the first and second constant current sources is provided by a resistor externally attached to the integrated circuit.
I ₂ ) can be controlled to control the gain.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a multipurpose filter to which an embodiment of the integrating circuit of the present invention is applied will be described below with reference to FIGS.

FIG. 2 shows an integrating circuit 21 used in this embodiment. In this figure, an input terminal 22 is connected to the base of an npn type transistor Q ₁ . Then, this transistor Q ₁ is differentially connected to another npn-type transistor Q ₂ . That is, the emitters of the transistors Q ₁ and Q ₂ are commonly connected via equivalent resistors 23 and 24, and this connection point is connected to the collector of the npn-type transistor Q ₈ . A reference voltage source 25 is connected to the base of the transistor Q ₂ .

The transistor Q ₈ is a constant current circuit (see FIG.
1A and 41B). That is, the power supply terminal 26 is connected to the anode of the diode 28 via the resistor 27, and the cathode thereof is grounded via the resistor 29. Then, the anode of the diode 28 is connected to the base of the transistor Q ₈ , and the emitter thereof is grounded via the resistor 30. The constant current of this constant current circuit is I
_Set to ₁ .

The collectors of the differentially connected transistors Q ₁ and Q ₂ have npn-type transistors Q ₃ and Q _{4, respectively.}
Connect the emitter of. These transistors Q ₃ , Q ₄
Each collector of is connected to the power supply terminal 26, and each emitter of is connected to the voltage source 31. These transistors Q ₃ and Q ₄ convert current into voltage by utilizing the forward characteristic of the pn junction. Then, a voltage corresponding to the collector current of the transistors Q ₁ and Q ₂ is obtained at each emitter.

The emitters of the transistors Q ₃ and Q ₄ are connected to the bases of the npn type transistors Q ₅ and Q ₆ , respectively. Transistors Q ₅ and Q ₆ are also differentially connected. That is, the emitters of the transistors Q ₅ and Q ₆ are commonly connected, and the connection point is connected to the collector-emitter path of the npn-type transistor Q ₉ and the resistor 32.
Ground through the series circuit of.

This transistor Q ₉ is also a constant current circuit (see FIG.
42A and 42B). That is, the power supply terminal 26 is connected to the anode of the diode 34 via the variable resistor 33, and the cathode of the diode 34 is connected to the resistor 3
Ground via 5. Then, the anode of the diode 34 is connected to the base of the transistor Q ₉ . The constant current of this constant current circuit is I ₂ . The above circuit is described in USP 3,676,789.

As will be described later, the gain of the integrating circuit is controlled by the ratio of the constant current I ₂ to the constant current I ₁ described above. Although this integrating circuit is composed of an IC (integrated circuit), the variable resistor 33 is externally attached and adjusted, and thereby the constant current I _{2, in} other words, the gain of the integrating circuit can be controlled.

The above-mentioned transistors Q ₅ and Q ₆ amplify the differential output obtained at the emitters of the transistors Q ₃ and Q _{4 in} the previous stage, and the amplified output is supplied to the capacitor 36 by the current mirror circuit. ing. That is, the collector of the transistor Q ₅ is connected to the power supply terminal 26 via the diode 37 connected in the forward direction, and the cathode of the diode 37 is connected to the base of the pnp type transistor Q ₇ . The emitter of the transistor Q ₇ is connected to the power supply terminal 26, the collector is connected to one end of the capacitor 36, and the output terminal 38 is led out from this connection point. Then, the other end of the capacitor 36 is grounded.

A constant current source 39 is connected in parallel to the capacitor 36. Constant current of the constant current source 39 is I _2/2. The collector current of the transistor Q _6, the operating point current of the collector current of the transistor Q ₇ in other words I _2/2
Therefore, only the signal current of the transistor Q ₆ is supplied to the capacitor 36.

In such an integrating circuit, in short, a current corresponding to the input signal Vin is supplied to the capacitor 36, and an integrated output of the input signal Vin is obtained as a voltage across the capacitor 36.

This will be described below. The current values and voltage values used in the following description are as shown in FIG.

That is, the collector currents I _C1 and I _C2 of the transistors Q ₁ and Q ₂ are And the base-emitter voltages V _be3 and V _be4 of the transistors Q ₃ and Q ₄ are Is. Here, I ₀ is the reverse saturation current, k is the Boltzmann constant, T is the absolute temperature, and q is the electron charge.

The base potentials V _b5 and V _b6 of the transistors Q ₅ and Q ₆ are As a result, the base-to-base voltage V _bb of the transistors Q ₅ and Q ₆ becomes the formula 1.

[0024]

[Equation 1]

[0025] On the other hand, the transistors Q _5, Q ₆ of the collector current of the signal components + i _out, when the -i _{ou t,} the base-emitter voltage of the transistor Q _5, Q ₆ is From this point, when the base-to-base voltage V _bb of the transistors Q ₅ and Q ₆ is obtained, the following equation 2 is obtained.

[Equation 2]

From the above equations 1 and 2 And this result Is established. And From I ₂ / I ₁ = r / R, the following equation 3 is obtained.

[0027]

[Equation 3]

From this, it can be seen that an integrated output is obtained from the output terminal 38.

In the above equation 3, r and r'are I
If the internal resistance of C is used, the temperature characteristic of the term r / r 'can be canceled. In this case, simply use the capacitor 3
The temperature characteristics of the integrating circuit 21 can be improved only by improving the temperature characteristics of the capacitance C of 6 and the resistance value R of the variable resistor 33.

Next, an embodiment of the multipurpose filter of the present invention using the integrating circuit 21 will be described with reference to FIG. In this example, the integrating circuit 21 of FIG. 2 is cascade-connected in two stages. In FIG. 3, the portions corresponding to those of FIG. 2 are designated by the corresponding reference numerals and detailed description thereof is omitted. Specifically, the suffix A is associated with the integrating circuit 21A in the first stage, and the suffix B is associated with the integrating circuit 21B in the subsequent stage. In FIG. 3, the constant current circuit formed by the transistor Q _{8 of} FIG.
The constant current circuit composed of the transistor Q ₉ is
Represented by 2A and 42B.

In FIG. 3, reference numerals 43 to 50 denote terminals,
A desired filter characteristic is obtained by selecting an input terminal and an output terminal from these terminals 43 to 50. The filter characteristics are low-pass filter, high-pass filter, band-pass filter, and trap characteristics.

In this example, the terminals 43 and 44 are connected to the resistor 51,
Via 52, they are respectively connected to the bases of the transistors Q _1A and Q _2A of the first-stage integrating circuit 21A. Terminals 45 and 46 are respectively connected to both ends of the capacitor 36A of the integrating circuit 21A of the first stage. And this capacitor 36
The base of the npn-type transistor 53 is connected to one end of the hot wire of A, the collector of the transistor 53 is connected to the power supply terminal 26, and the emitter thereof is grounded via the constant current circuit 54. This transistor 53 constitutes an emitter follower circuit, and its emitter is fed back to the base of the transistor Q _2A through the resistor 60 and the resistor 5
It is connected via 5 to the base of the transistor Q _1B of the integrating circuit 21B at the next stage.

Transistor Q _1B of the integrating circuit 21B at the next stage
A terminal 47 is also connected to the terminal via a resistor 56. Also,
Terminals 49 and 50 are derived from both ends of the capacitor 36B of the integrating circuit 21B at the next stage, and the base of the transistor 57 forming the emitter follower circuit is connected to one end of the hot wire. The collector of the transistor 57 is connected to the power supply terminal 26. Then, the emitter is grounded via the constant current circuit 58 and connected via the resistor 59 to the base of the transistor Q _1A of the integrating circuit 21A at the first stage.

Next, the operation of this embodiment will be described. Here, the equation 3 obtained for the integrating circuit 21 of FIG. 2 is first applied to this FIG. The signal voltages V _{1 to} V ₈ and the resistance values ra, ra ', rb, rb',
rc and rc 'are as illustrated.

In the integrating circuit 21A at the first stage, the base voltage of the transistor Q _1A is the input voltage V _b1. And the base of the transistor Q _2A is the input voltage V _b2
But Is. These are obtained from the theory of superposition. The input signal Vin is Vin = _Vb1 − _Vb2 . Therefore, the output voltage of the integrating circuit 21A, that is, the voltage V ₀₁ between both ends of the capacitor 36A is given by the equation 4.

[0036]

[Equation 4]

However, And Further, in this case, Expression 5 is established.

[0038]

[Equation 5]

[0039] Similarly, the integration circuit 21B of the next stage
For, the equations 6 and 7 hold.

[0040]

[Equation 6]

[0041]

[Equation 7]

Is satisfied. However, V ₀₂ is capacitor 3
Is the voltage across 6B, And

Next, what kind of filter characteristics can be obtained by selecting the terminals 43 to 50 will be described.

(1) When the terminal 50 is the input terminal and the terminal 45 is the output terminal.

That is, this is the case where V ₇ = V _out and V ₆ = V _in . Note that V ₁ , V ₂ , V ₃ , V ₄ , and V ₅ = 0. Substituting these V _{1 to} V ₇ into Equation 4 and Equation 5, From which we obtain the number 8.

[0046]

[Equation 8]

Similarly, by substituting V _{1 to} V ₇ into the equations 6 and 7, the equation 9 is obtained.

[0048]

[Equation 9]

Then, by substituting this equation 9 into the previous equation 8, To get From this, it can be seen that a bandpass output is obtained from the terminal 45 as an output terminal.

(2) When terminals 46 and 48 are input terminals and terminal 45 is an output terminal.

That is, V ₇ = V _out , V ₃ = V ₅ = V
_{This is} the case for in. Note that V ₁ , V ₂ , V ₄ , and V ₆ = 0. Substituting these V _{1 to} V ₇ into Equation 4 and Equation 5, And obtain the number 10 from them.

[0052]

[Equation 10]

Similarly, by substituting V _{1 to} V ₇ into Equations 6 and 7, Equation 11 is obtained.

[0054]

[Equation 11] Substituting this number 11 into the number 10 To get From this, it can be seen that in this case, the trap output is obtained from the terminal 45 as the output terminal.

(3) When the terminal 48 is the input terminal and the terminal 45 is the output terminal.

That is, this is the case where V ₇ = V _out and V ₅ = V _in . Note that V ₁ , V ₂ , V ₃ , V ₄ , V ₆ =
Set to 0. Substituting these V _{1 to} V ₇ into Equation 4 and Equation 5, And get the number 12 from these

[0057]

[Equation 12]

Similarly, by substituting V _{1 to} V ₇ into Equations 6 and 7, Equation 13 is obtained.

[0059]

[Equation 13]

By substituting this equation 13 into the equation 12, To get From this, it can be seen that in this case, the low-pass output is obtained from the terminal 45 as the output terminal.

(4) When the terminal 44 is the input terminal and the terminal 45 is the output terminal.

That is, this is the case where V ₇ = V _out and V ₂ = V _in . Note that V ₁ , V ₃ , V ₄ , V ₅ , V ₆ =
Set to 0.

Substituting these V _{1 to} V ₇ into the equations 4 and 5, And obtain the number 14 from these.

[0064]

[Equation 14]

Similarly, by substituting V _{1 to} V ₇ into the equations 6 and 7, the equation 15 is obtained.

[0066]

[Equation 15]

By substituting this equation 15 into the equation 14, To get From this, it can be seen that in this case, a bandpass output is obtained from the terminal 45 as an output terminal.

In this case, a trap output is obtained by selecting the base of the transistor Q _2A of the first-stage integrating circuit 21A as the output terminal. That is, in this case, V _out =
b′V ₇ + bV ₂ , and substituting this equation for each of the above equations instead of V _out = V ₇ To get From this, it can be seen that the trap output is also obtained in this case.

As described above, according to this example, various filter characteristics can be obtained by selecting the input terminal and the output terminal. In this case, it is not necessary to discretely connect the operational amplifier and various CR network as described above,
The configuration can be extremely simplified. Further, the transfer function in each filter characteristic is the characteristics S ₁ and S of the integrating circuits 21A and 21B.
₂ and ra, ra ', rb, rb', rc, rc ', which means that the temperature characteristics of these transfer functions are I
It means that it becomes extremely improved by conversion to C. When selecting components, it is only necessary to pay attention to the capacitors 36A and 36B and the variable resistor 33.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the spirit of the invention.

[0071]

According to the integrating circuit of the present invention, a diode load is connected to a first differential amplifier having a first constant current source connected to a commonly connected emitter, and a diode load is provided across the diode load. The logarithmically converted voltage is supplied to a second differential amplifier in which a commonly connected emitter is connected to a second constant current source, and one of the pair of outputs of the second differential amplifier is directly used as a current mirror circuit. Because it is taken out through
There is an advantage that the dynamic range of the output signal component can be made large. Further, there is an effect that the gain can be controlled by controlling the current ratio of the first and second constant current sources by the externally attached resistor.

In particular, the circuit in which the integrating circuits are cascade-connected in two stages has a simple structure and is useful as a multipurpose filter excellent in temperature characteristics.

[Brief description of drawings]

FIG. 1 is a circuit showing a multipurpose filter to which an integrating circuit according to a conventional technique is applied.

FIG. 2 is a circuit diagram showing an embodiment of an integrating circuit of the present invention.

FIG. 3 is a circuit diagram showing a multipurpose filter to which an integrating circuit according to the example of FIG. 2 is applied.

[Explanation of symbols]

21 Integrator circuit 36 Capacitor 37 Q ₇ Diode and transistor forming current mirror circuit Q ₁ and Q ₂ Transistor forming differential amplifier Q ₃ and Q ₄ Transistor forming differential amplifier

Claims (1)

[Claims] 1. A pair of diode loads are connected to a first differential amplifier, which is formed by connecting a first constant current source to the emitters of commonly connected first and second transistors, and the first transistor is connected to the first differential amplifier. A second constant current source connected to the emitters of the commonly connected third and fourth transistors by supplying an input signal to the base of the second transistor, applying a reference voltage to the base of the second transistor, The logarithmic-converted voltage obtained across the pair of diode loads, and one of the pair of outputs of the second differential amplifier is supplied to the capacitor via the current mirror circuit. An integrated circuit in which a third constant current source having a current value of 1/2 of the value of the second constant current source is connected in parallel to the capacitor, and the integrated circuit is configured by an integrated circuit. With an external resistor Thus, an integrator circuit for controlling the gain by controlling the current ratio of the first and second constant current sources.