JPH0519846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a feedback type integrating circuit applied to a secondary active filter.

"Background Art and its Problems" When realizing a high Q configuration with a secondary active filter, an integrating circuit (low-pass filter) with small loss is required. Considering the IC circuit, it is not possible to use large capacity capacitors, so
Increase the resistance inserted in parallel with the capacitor,
It is possible to reduce losses.

Conventional integrating circuits reduce loss by increasing the collector resistance by increasing the impedance of the current source. However, this method has limitations in terms of characteristics, and it has not been possible to obtain higher Q filter characteristics.

Generally, a current source at the collector output of a transistor has a resistance component due to the Early effect, but its value decreases in inverse proportion to the emitter current value. Therefore, even if the collector resistance is increased by increasing the resistor inserted into the emitter, the emitter current becomes small and the collector resistance cannot be increased very much. However, as the emitter resistance increases,
The dynamic range becomes narrower. For this reason, it is necessary to increase the power supply voltage to increase the dynamic range, which is not favorable for IC implementation.
Therefore, the method described above to increase the collector resistance of the transistor has a problem.

Further, when using current sources of NPN type transistors and PNP type transistors, the difference in conductivity type causes variations in resistance due to the Early effect, which has the disadvantage of causing variations in characteristics.

``Object of the Invention'' The object of the present invention is to provide an integrating circuit in which the collector resistance connected in parallel with the capacitor is increased to a very large value by feedback, and thereby the loss is small.

In addition, this invention eliminates variations by utilizing the collector resistance of the transistor itself.
This realizes an integrating circuit that has stable characteristics against temperature changes.

Furthermore, another object of the present invention is to be able to operate with a low voltage power supply and use small capacitors;
The object of the present invention is to provide an integrating circuit suitable for IC circuits.

"Summary of the Invention" This invention supplies a first input signal current to a capacitor through an emitter-collector path of a first common-base transistor, and supplies a second signal current that is in opposite phase to the first signal current. A current is supplied to the input circuit side of the current mirror circuit through the emitter-collector path of the second common-base transistor and the emitter-collector path of the third transistor, and the output circuit of the current mirror circuit is connected to the capacitor. , is a feedback type integrating circuit that supplies the output current of a current mirror circuit to a capacitor, and also derives the voltage obtained across the capacitor to an output terminal via a base-emitter path of a third transistor.

Embodiment In FIG. 1 showing a circuit configuration of an embodiment of the present invention, 1 is a first common-base type PNP transistor, and 2 is a second common-base type PNP transistor. The emitter of transistor 1 is connected via resistor 21 to power supply terminal 18 to which power supply voltage +V _CC is supplied, and the emitter of transistor 2 is connected to power supply terminal 18 via resistor 22 . A first input terminal 15 is connected to the emitter of transistor 1, and a second input terminal 16 is connected to the emitter of transistor 2. First and second signal currents of opposite phases are supplied to input terminals 15 and 16 from a differential amplifier (not shown) at the previous stage, respectively.

The collector of transistor 1 connects to NPN transistor 6 through the base-emitter junction of PNP transistor 3, whose base and collector are connected.
The emitter of the transistor 6 is connected to the ground terminal 19 via a resistor 23. The collector of the transistor 2 is connected to the emitter of a third PNP transistor 4, and the collector of the transistor 4 is connected to the ground terminal 19 via the base-emitter junction of the NPN transistor 7, to which the base-collector is connected, and the resistor 24. Ru. Further, a connection point between the collector of the transistor 2 and the emitter of the transistor 4 is connected to the collector of the NPN transistor 8 and the base of the NPN transistor 10. The emitter of transistor 8 is connected to ground terminal 19 via resistor 25. Furthermore, the first input terminal 15 and the NPN transistor 5
The collector of transistor 5 is connected to the emitter of transistor 7, and the emitter of transistor 5 is connected to the emitter of transistor 7. These NPN transistors 5, 6, 7, 8
the bases of are connected to each other.

Further, a capacitor 14 is inserted between the bases of the transistors 3 and 4 and ground. transistor 10
is configured as a pair with PNP transistor 9, and the connection point between the emitters of transistor 9 and transistor 10 is derived as output terminal 17. The emitter of this transistor 10 is the NPN transistor 11
It is connected to the ground terminal 19 via the collector-emitter path of the resistor 26 and the resistor 26.

The emitter of PNP transistor 12 is resistor 27
It is connected to the power supply terminal 18 via the power supply terminal 18, and its base and collector are connected to each other. transistor 1
The base-collector connection point of 2 is connected via resistor 28.
It is connected to the collector-base connection point of the NPN transistor 13. The emitter of this transistor 13 is connected to a ground terminal 19 via a resistor 29. A base-collector connection point of transistor 12 is connected to the bases of transistor 1 and transistor 2, and a base bias voltage is supplied to transistors 1 and 2. The base of transistor 11 is connected to the base-collector connection point of transistor 13, forming an emitter current source of transistor 10.

The above transistors 5, 6, 7, 8 and resistor 2
3, 24, and 25 constitute a current mirror circuit. In other words, the emitter current of transistor 7 is I
Then, a current of I flows through transistor 5, and a current of I' (=kI) flows through transistors 6 and 8.
The coefficient k is determined by the relationship between the values of the resistors 23 and 25 and the value of the resistor 24. The difference between the current supplied through the base-emitter junctions of transistors 1 and 3 and the current flowing into the collector of transistor 6 becomes the charging current of capacitor 14.

FIG. 2 shows an AC equivalent circuit of an embodiment of the present invention. For ease of explanation, this equivalent circuit is expressed by an ideal current source and a collector conductance due to the Early effect.

In FIG. 2, 31 is an input signal current source of signal current I ₁ constituted by transistor 1, G ₁
is the collector conductance of transistor 1,
Reference numeral 32 denotes an input signal current source of signal current I ₂ constituted by transistor 2, and G ₁ is collector conductance of transistor 2 (equal to that of transistor 1). Furthermore, currents flowing through transistors 5, 6, and 8, respectively, are represented by current sources 35, 36, and 38 due to the current mirror circuit. The current of current source 35 is I, and the currents of current sources 36 and 38 are
I', and the collector conductances of transistors 36 and 38 are shown as _G2 .

Furthermore, if only the feedback component is considered, excluding the input signal system current, the equivalent circuit of FIG. 2 becomes the one shown in FIG. 3. In FIG. 3, D is the base-emitter junction of transistor 3.

Now, the electric charge in capacitor 14 is being charged.
Assuming that the potential is V ₂ , if there is no feedback current source 36 , the capacitor 14 will discharge until the currents flowing through each of the conductances G ₁ and G ₂ are equal, and the voltage will increase from V ₂ to G ₁ /G ₁ The potential changes to +G ₂・(V _CC −V _BE ).

Here, if the current flowing into the emitter of transistor 4 is ΔI, then ΔI=G ₁ V ₁ − G ₂ (V ₂ +V _BE )...(1) Also, in order to maintain the base side potential V ₂ of transistor 4, Similarly, since a current of ΔI′ must flow, ΔI′=G ₁ V ₁ − G ₂ V ₂ ……(2). However, the current ΔI flowing into the emitter of the transistor 4 shown in equation (1) is multiplied by α (α≒1, α<1) by the current mirror and enters the base, so it is subtracted as ΔI′−αΔI=(1− α) G ₁ V ₁ − (1 − α) G ₂ V ₂ + αG ₂ V _BE ……(3). Comparing equations (2) and (3), αG ₂
Except for the V _BE term, the collector conductances of transistors 1 and 2 are (1-α)G ₁ , (1
−α) It can be seen that it becomes smaller as G ₂ . In other words,
The feedback current source 36 reduces the conductance (increases the resistance value). Furthermore, the term αG ₂ V _BE is a current value that is not related to the potential of the capacitor, so it does not become a conductance component in terms of alternating current.

In this way, transistors 1, 2, 3, 4, 6, and 7 are basically required to provide feedback. The transistor 8 is connected to the base and emitter of the transistor 4 so that the conductance thereof is equal to (G ₁ +G ₂ ), thereby increasing the resistance value. Furthermore, if the respective collector currents of transistor 1 and transistor 2 are equal, and the collector currents of transistor 6 and transistor 8 are also equal, then the current flowing through transistor 4 will disappear, so only the current flowing through transistor 4 will be equal. , the current of transistor 2 must be increased. For this reason, the transistor 5 is provided, the current value of the transistor 1 is made small, and the current value of the transistor 2 is made relatively large.

Further, in one embodiment of the present invention, as is clear from the equivalent circuit shown in FIG. 3, when the value of the capacitor 14 is C, (G ₁ +G ₂ =G ₀ ), and the output voltage is V ₀ , The following transfer characteristic is obtained.

I ₁ −I′−I/SC+G ₀ =V ₀ ...(4) Also, the current I flowing through the collector of transistor 4
I=I ₂ −I′−G ₀ V ₀ ……(5) From equations (4) and (5), if I and I′ are eliminated, (5)
From the formula, (I′+I=I ₂ −V ₀ G ₀ ). This (4)
By substituting it into the equation, it becomes I ₁ −(I ₂ −V ₀ G ₀ )/SC+G ₀ =V ₀ ∴V ₀ /I ₁ −I ₂ =1/SC.

In the embodiment of the present invention described above, basically, as shown in FIG. 4, a parallel circuit of an input signal current source _I1 and a collector conductance component _G0 is connected to a capacitor
4, the feedback current source 36 (conductance G ₀ ) is further connected in parallel using a current mirror circuit. With this feedback current source 36,
The collector conductance component G ₀ can be canceled out, and loss can be reduced.

FIG. 5 shows an example of the input/output (V _i /V ₀ ) characteristics of the embodiment of the invention described above. The ideal integrator (ω ₀ /S) has a slope characteristic of −6 dB/oct, but this embodiment has a slope characteristic of (−3 dB) at (f ₁ =216 Hz). That is, it has the characteristics shown as ω ₀ /S+ω ₁ =V ₀ /V ₁ f ₀ =ω ₀ /2π=84.6kHz f ₁ =ω ₁ /2π=216Hz. The value of capacitor 14 is 15pF,
If the stray capacitance 20 (see Figure 1) is 1.5 pF, then
When the collector current of transistor 3 is 50μA, the apparent parallel resistance value R is R=1/2πf ₁ C = 1/2π×216×16.5×10 ^-12 ≒44.7MΩ, which is the value without feedback (200KΩ~ 300KΩ)
This is an improvement of more than 100 times compared to

"Effects of the Invention" According to this invention, by increasing the value of the resistor connected in parallel with the capacitor, it is possible to realize an integrating circuit with a large loss, and when applied to an active filter, it is possible to realize a high Q filter. can be configured.

In addition, this invention differs from increasing the emitter resistance in increasing the collector resistance.
This eliminates the problem of narrowing the dynamic range, enables a low-voltage power supply configuration, and provides an integration circuit suitable for IC implementation.

Furthermore, since this invention has a circuit configuration that utilizes the collector conductance itself of the transistor, the relative change with respect to temperature and variation is the same even though its value is small.
This has the advantage that a very stable circuit configuration can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of an embodiment of this invention, Figs. 2 and 3 are connection diagrams of an AC equivalent circuit of an embodiment of this invention, and Fig. 4 is a basic configuration of an embodiment of this invention. FIG. 5 is a graph showing input/output characteristics of an embodiment of the present invention. 1... first common base transistor, 2...
...Second base-grounded transistor, 4...Third
transistors, 15, 16...input terminals, 17
...output terminal, 18...power terminal, 19...ground terminal.

Claims (1)

[Claims] 1 a first common base type transistor whose emitter is connected to a first reference potential via a first resistor and to which a first input signal is supplied; a second common base transistor connected to the reference potential of the first transistor and supplied with a second input signal having a phase opposite to the input signal; an emitter connected to the collector of the first transistor; a third transistor connected to the collector and the other end of the capacitor whose one end is connected to the second reference potential; the emitter is connected to the collector of the second transistor, and the base is connected to the second transistor; a fourth transistor connected to the base of the third transistor;
a sixth transistor whose collector and base are both connected to the collector of the fourth transistor, and whose emitter is connected to the third reference potential via a fourth resistor, and whose base is the base of the sixth transistor; The collector is connected to the collector of the third transistor, and the emitter is connected to the third transistor.
a fifth reference potential connected to a third reference potential through a resistor of
a seventh transistor whose collector is supplied with the first input signal and whose base and emitter are respectively connected to the base and emitter of the sixth transistor.
A feedback type integrating circuit comprising a transistor, and an output signal is taken out from the collector of the second transistor.