JPH01290309A - Filter circuit - Google Patents

Abstract

PURPOSE:To facilitate the characteristic adjustment even if the resistance is dispersed in an IC by varying the resistance of a resistor mounted externally to the IC so as to change the inductance of an equivalent inductance circuit. CONSTITUTION:An equivalent inductance is formed by a transconductance gm2 of a differential two-stage amplifier circuit 61, a transconductance gm1 of a differential amplifier circuit 62, a capacitance CL of a load 36 of the said amplifier circuit 61 and sum R12 of emitter dynamic resistances of two transistors (TRs) 39, 40, and an RLC filter is constituted by the equivalent inductance and a capacitor 42 connected to an output terminal and the entire circuit is constituted by an IC except a variable resistor 56. Since the said conductances gm1, gm2 are varied by varying the current of the absolute temperature proportional variable constant current circuit 60 through the adjustment of the resistance of the said variable resistor 56, then the inductance is varied equivalently and the cut-off frequency of the filter circuit is varied at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an RLC low-pass filter circuit suitable for semiconductor integrated circuits.

[Conventional technology]

With the spread of consumer and AV products, there is a strong desire for analog filter integrated circuits (hereinafter referred to as rIcJ) capable of processing video signals of approximately several MHz. An RLC filter is one type of analog filter, but current IC technology does not allow the use of inductance elements as circuit elements. Therefore, when converting an RLC filter into an IC, it is necessary to use passive or active elements other than inductance elements. There is a method of synthesizing equivalent inductance circuits and designing an RLC filter circuit. However, this configuration has the problems of requiring many elements to configure the equivalent inductance circuit and increasing the power consumption of the circuit, and has traditionally been considered impractical for practical use.

Conventional RLC filter circuits devised to solve the above problems include, for example, (1984 IEEE In
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Negative impedance converter (Negative impedance converter).

An example of this is an RLC filter circuit as shown in FIG. 6, which uses an RLC filter (rNIcJ) (hereinafter referred to as rNIcJ).

FIG. 7 shows an example of a second-order RLC low-pass filter circuit. In the figure, (1) is an input signal source, and this input signal source (
1) is grounded via a battery (2), and the other end of this input signal source (1) is connected to a Jlpn type transistor (
3), the emitter of this transistor (3) is connected to one end of a resistor (0), the other end of this resistor (4) is grounded via a constant current source (5), and this The other end of the resistor (0) is connected to one end of the resistor (8), the other end of this resistor (6) is connected to the emitter of the npn transistor (7), and the base of this transistor (7) is connected to the battery. (8) to ground.Also, transistor (3)
The collector of the transistor (3) is connected to the collector of the transistor (7) via a capacitor (9) with a capacitance of C, and the collector of the transistor (3) is connected to a resistor (10) with a resistance of RGI.
The other end of this resistor (10) is connected to the emitter of an NPN type H transistor (11), and the base of this transistor (11) is grounded via a constant current source (12). The base of this transistor (11) is n
Connect the emitter of the pn type transistor (13), connect the collector of this transistor (13) to the power supply terminal (14), connect the base of this transistor (13) to the collector of the npn type transistor (IS), and connect the collector of this transistor (13) to the power supply terminal (14). The base of the transistor (13) is connected to the emitter of the npn transistor (1B). Also, the transistor (
The emitter of the transistor (15) is connected to the collector of the transistor (7) via a resistor (17) with a resistance value RGI, and the base of the transistor (15) is grounded via a constant current source (18). IS) based on np
It is connected to the emitter of an n-type transistor (18), the collector of this transistor (IS) is connected to the power supply terminal (14), the base of this transistor (18) is connected to the collector of the transistor (11), and the npn-type The base of this transistor (20) is connected to the collector of this transistor (2Q), and the connection point between the base and collector of this transistor (20) is connected to the resistor (21) with a resistance value RG2. ) to the 'rL source terminal 4), and connect the connection point between the base and collector of this transistor (20) to the capacitance C
The other end of this capacitor (22) is connected to the power supply terminal (14) via a resistor (23) with a resistance value RG2, and the other end of this capacitor (22) is connected to one end of a capacitor (22) of L. The end of the transistor (1B) is connected to the collector of the transistor (16), the collector of this transistor (16) is connected to the base of the transistor (16), and the transistor (20
) is derived from the connection point between the collector and base of the transistor (1B), and a terminal (25) is derived from the connection point between the collector and base of the transistor (1B), and the voltage taken out to the terminal (25) and the terminal (24 ) is configured to derive the difference voltage between the voltages taken out as the output voltage.

Next, the operation will be explained. In FIG. 7, the input signal voltage of the input signal source (1) is V in, and the signal current flowing from the transistor (3) to the transistor (7) via the resistors (4) and (8) due to the input signal is i, Let RE be the resistance values of resistors (4) and (6), respectively, and the sink current by constant current source (5) is sufficiently large, and the emitter dynamic resistance of transistors (3) and (7) is equal to that of resistor (4).
) and (6), the following holds true.

Also, among the signal current i, a resistor (17
) to transistor (15), (1B), resistor R
G2 resistors (23), (21) and - capacitance value C
The transistor (20
), (11') and the signal current flowing through the resistor (lO) with resistance value RGI is 11, the signal voltage taken out from the terminal (24) is Vl, the signal voltage taken out from the terminal (25) is V2, and the output voltage If Vout is the angular frequency of the signal and ω is the angular frequency of the signal, then Vout=V2−Vl holds true.

On the other hand, if the signal current flowing through the capacitor (9) with a capacitance value C out of the signal current i is 12, then 1=il++2
(3) Here, Zin is the input impedance when the circuit network through which the signal current i1 flows is viewed from both ends of the capacitor (9). Here, the capacitor (
The signal voltage appearing at the connection point between 9) and resistor (10) is V3.
．． Similarly, if the signal voltage appearing at the connection point of the capacitor (9) and resistor (17) due to the signal current 11 is 4, then the input impedance when the circuit network through which the signal current i1 flows is viewed from both ends of the capacitor (9). Zin is given by. Here, the signal voltage appearing at the bases of transistors (18) and (13) due to signal current 11 is V5. If V 8 and the emitter dynamic resistance of transistors (16) and (20) are each tel, then V6 -V5 =V2 -Vi +2 a rel@il
...(6), and furthermore, the signal voltages appearing at the bases of transistors (11) and (15) are respectively V.
7. V B, transistors (13) and (1
9) constitutes the emitter pho 07 circuit, V5 = V8
, VEI = V7 ,! ：VB −V7 = −(VB −V5 )
・-(7). Further, the signal voltages appearing at the emitters of transistors (11) and (15) due to signal voltage 11 are respectively VB and VIO, and the emitter dynamic resistances of transistors (11) and (15) are r, respectively.
If e2= (r el), then V 10- V 9 = V8-V7 +2 Φre2-i1 - (8), and 4-V3 = V 10- VB + 2- RGIlli 1
−(9), therefore (6), (7), (8
) and (9) formula % formula % are obtained. Also, from equation (2), equation (lO) is V4-V
3 = (2・RGI), so the input impedance Zin when the circuit network through which the signal current 11 flows is viewed from both ends of the capacitor (3)
is established from equations (5) and (8).

Therefore, from equations (3), (4), and (12), +1= ・RG2 Tree□ @i...(13) @(RGI-RG2) Therefore, equations (1), (2), and (13) Find the transfer function H(ω) of this circuit from If the resistance value is determined, equation (14) becomes G H(ω)=□ 2・RE 木□ ...(15)+1, which means that the cutoff ωC is ■ 0° ) indicates that Q is a second-order low-pass filter.

:The low-pass filter circuit shown in Figure 57 is in principle the 8th filter circuit.
This is an example in which a filter circuit is constructed by equivalently synthesizing inductance using the NIC shown in the figure. That is, using the NIC shown in FIG. 8, a circuit is constructed as shown in FIG. 9, and resistors (10) and (17) are connected.

If the resistance values of (2+) and (22) are respectively RG/2, the circuit in FIG. 9 can be replaced with the equivalent circuit shown in FIG. 10, and in this FIG. If it is terminated with a capacitor, the terminal T5. T [1
The input impedance when expected from is equivalently a resistor (2θ) with a resistance value RG and an inductance value CL-R.
It is equal to the impedance value when the G2 inductors are connected in parallel.

[Problem to be solved by the invention]

The conventional RLC low-pass filter circuit shown in FIG.
A filter circuit is constructed by synthesizing the equivalent inductance with a small number of elements, but when this is integrated into an IC, the accuracy of the resistance and capacitance values within the IC is poor, so the cutoff frequency of the filter varies, and However, since the temperature characteristics of the resistance value are poor, the temperature characteristics of the cutoff frequency are also poor.

This invention was made to solve the above problems, and even if the resistance value and capacitance value vary within the IC, the IC
An object of the present invention is to obtain an RLC low-pass filter circuit whose cutoff frequency can be externally controlled and which has good temperature characteristics.

[Means to solve the problem]

The filter circuit according to the present invention is configured to be determined by the values of the transconductance of the differential two-stage amplifier circuit and the transconductance of the differential amplifier circuit constituting the filter circuit, and the values of these transconductances are determined. This device is configured to obtain filter characteristics using an equivalent inductance circuit configured so that the value of input impedance can be varied by adjusting the magnitude of the current flowing through the current source, and a capacitor.

[Effect]

The filter circuit according to the present invention has a transconductance of a differential two-stage amplifier circuit that is 2. From the input and output terminals, where gl is the differential amplifier circuit transconductance, CL is the capacitance value of the first capacitor that constitutes the load of the differential two-stage amplifier circuit, and R1 is the sum of the emitter dynamic resistances of the two transistors. The equivalent inductance of the expected input impedance and the second capacitor connected to the output terminal act as a second-order RLC filter, and the above g1 and g+i2 are proportional to the current value of the constant current power supply. Therefore, by changing the current value of the constant current source, the inductance value can be changed isometrically, and at the same time, the cutoff frequency of the filter circuit can be changed.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram of an embodiment of this invention in which equivalent inductances are synthesized to form a second-order RLC low-pass filter. In figure 0, one end of the input signal source (1) is connected to the base of the npn transistor (27). At the same time, the other end of this input signal source (1) is grounded via a battery (2), the collector of this transistor (27) is connected to the power supply terminal (14), and the emitter of this transistor (27) is connected to a diode. It is connected to the connection point between the base and collector of the connected npn transistor (28), and this transistor (28
) is connected to the emitter of a pnp transistor (29), the collector of this transistor (29) is grounded, the base of this transistor (29) is connected to the base of a pnp transistor (30), and this transistor (29) is grounded via a battery (31), the collector of this transistor (30) is grounded, the emitter of this transistor (30) is connected to the emitter of an npn transistor (32), and this transistor (
Connect the connection point between the base and collector of the transistor (32) to the emitter of the npn transistor (33).
33) is connected to the power supply terminal (14).

Also, the emitter of the transistor (28) and the transistor (
The connection point of the emitter of 2B) is connected to the npn transistor (3B).
4), the emitter of this transistor (34) is connected to the emitter of an npn transistor (35), and the base of this transistor (35) is connected to the emitter of transistor (32) and the emitter of transistor (30). The collector of this transistor (35) is connected to the collector of a transistor (34) via a capacitor (38) with a capacitance value of CL, and the collector of this transistor (35) is connected to an npn type transistor ( This transistor (37) is connected to the base of the transistor (37).
) is connected to the emitter of the npn transistor (38), the base of this transistor (3B) (7) is connected to the collector of the transistor (34) by 11i, and the base of this transistor (38) is connected to the emitter of the npn transistor (38). The base of this transistor (33) is connected to the base of an npn transistor (40), and the base of this transistor (39) is grounded via a battery (41). 39) and the collectors of the transistor (40) are both connected to the power supply terminal (14). Also, transistor (38)
Connect the collector of to the base of the transistor (33),
Collector of transistor (38) and transistor (33)
) with a capacitor (42
), and an output terminal (43) is led out from the base of the transistor (33). Further, the collector of the transistor (37) is connected to the base of the transistor (27), the collector of this transistor (37) is connected to the collector of a pnp transistor (44), and the emitter of this transistor (44) is connected to the power supply terminal ( 1
0 and connect the base of this transistor (44) to Pn
Connect to the base of the P-type transistor (45), connect the emitter of the transistor (45) to the power supply terminal (14),
Connect the collector of this transistor (45) to the transistor (
38) collector. Also, a transistor (34
) is connected to the emitter of the emitter transistor (35) to the collector of an npn transistor (46), and the emitter of this transistor (46) is grounded.

Also, connect the connection point between the emitter of the transistor (37) and the emitter of the transistor (38) to the npn transistor (
47), and this transistor (47)
The emitter of the transistor (47) is grounded, and the base of the transistor (47) is connected to the base of the transistor (4B). In addition, the connection point between the base of the transistor (44) and the base of the transistor (45) is connected to the base of an npn transistor (48), the collector of this transistor (48) is connected to the power supply terminal (14), and this transistor (48)
While grounding the emitter of via the resistor (48),
The emitter of this transistor (48) is connected to the base of a pnp transistor (50), and this transistor (
The collector of the transistor (50) is connected to the connection point between the base of the transistor (4B) and the base of the transistor (47), and the emitter of this transistor (50) is connected to two pnp transistors (50) whose emitter bases and collectors are connected in common. 51) and (51a), the emitter of this transistor (50) is connected to the collector of an npn transistor (52), and the common emitter of transistors (51) and (51a) is connected to the power supply terminal (14). ) and connect this transistor (
51) and (51a) is connected to the transistor (
4) and the base of this transistor (
51) and (51a) are connected to the emitter of a pnP transistor (53), the collector of this transistor (53) is grounded, and the
) is connected to the collector of the pnp transistor (54), the emitter of this transistor (54) is connected to the power supply terminal (14), and the base of this transistor (54) is connected to the collector of the transistor (51) and (51a). Connect to the connection point between the base and the emitter of the transistor (53). Also, the emitter of the transistor (52) is grounded, and the base of this transistor (52) is connected to the transistor (50).
and the base of the transistor (52) are connected to the connection point between the collector of the transistor (55) and the base of the transistor (47), and the base of the transistor (52) is connected to two npn transistors (55) and (55a) whose emitters, bases, and collectors are respectively commonly connected. ), and the common collectors of these transistors (55) and (55a) are connected to the connection point between the base of transistor (53) and the collector of transistor (54), and the transistors (55) and (55a) Connect the common emitter of the resistor (5B) with resistance value H.
It is grounded through. In this circuit configuration,
Transistors (40-(48), (50)-(55a)
) and resistors m (413) and (56) constitute an absolute temperature proportional constant current generating circuit shown in Japanese Unexamined Patent Application Publication No. 180597/1983 which has four output terminals, and resistor (5B)
By using a variable resistor, the transistor (44)
- (47) constitute an absolute temperature proportional variable constant current circuit (hereinafter referred to as "constant current circuit") (60) which can be adjusted while maintaining the same current value by using four output terminals.

Also, transistors (27) to (30), (32) to
(35).

(39) and (40) constitute a differential two-stage amplifier circuit (61), and further transistors (37), (38), (
44) and (45) form the differential amplifier circuit (82). Next, the operation will be explained. In Figure 1, the input voltage of the input signal source (1) is Vin, the output voltage derived from the output terminal (43) is Vout,) transistors (27), (28), (29), (
30), (32) and (33), respectively, as r e27. r e28. r e29.
r e30° r e32 and r e33, and the input signal causes the signal to flow from the emitter of the transistor (27) through the transistors (2B), (29), (30) and (32), and from the emitter of the transistor (27) to the transistor (2B) by the trans signal. ) , (2θ), (30) ,
If the signal current flowing into the base of the transistor (33) through (32) is il, then the following holds true. Here, transistors (27), (28), (29), (30
), (32) and (33), the DC component of the current flowing through the emitter is assumed to be 11, and the relationship between the emitter current of the transistor and the emitter dynamic resistance re, where k: Pollmann's constant T: absolute temperature q: electron If you use the charge of re27 + re28 + re29 + r
e30 + re32+re33 So, substitute equation (20) into equation (18)! fq-I
+, ...(21) (Vin-Vout)°6. k, T=s 1. Also, transistors (29), (30),
The base-emitter voltage of (34) and (35) is set to VBE29. VBE30. VBE34t-
J Yobi VBE35 to sushi if, V BE29- V B
E34=VBE30-VBE35-(22
) holds true.

Here, the signal current flowing from the emitter of the transistor (34) to the base of the transistor (35) is 12, the current sucked by the transistor (4B) forming the constant current circuit (SO) is 2I2, if the transistor (34)
) and the emitter current flowing through the transistor (35) are I2++2 and 2-i2, respectively, and the relationship between the emitter 1ikIe of the transistor and the base-emitter voltage VBE is: Here, if S: saturation current is used, ( Formula 22) uses the relationship of formula (23)...(24) Coconi, I s29. I s34. I s30.
I s35 are transistors (29) and (34), respectively.
, (30) and (35).

By the way, in the same IC chip, l529 =
Since l534- l530 = l535,
The equation (24) becomes the following by substituting the equation (21) into the equation (25).

By the way, this signal current 12 flows into the parallel circuit of the emitter dynamic resistance of the transistors (39) and (40) and the capacitor (3B) with a capacitance value CL, so that the base of the transistor (37) and the base of the transistor (38) are connected to each other. The signal voltage V1 generated between the transistors (38
) and (40), respectively r e3
9 and re40, and the angular frequency of the signal is ω. However, since it is a relation of equation (19), equation (27) becomes 2− to −T from equation (28).

Signal voltage (f&i) 3, which flows from the emitter of the transistor (37) through the transistor (38) to the capacitor (42) with a capacitance value C due to this signal voltage ■1, increases the emitter dynamic resistance of the transistors (37) and (38), respectively. e37 and r e38, and here, if the sink current by the transistor (47) that constitutes the constant current circuit (60) is 2I3, then equation (30) becomes (19
) from the relationship of the equation. When this signal current i3 flows into the capacitor (42) with a capacitance value C, a signal voltage is generated and taken out from the output terminal (43). Therefore, the signal voltage generated by the capacitor (42) with a capacitance value C is the output voltage V It is out. Therefore, holds true.

Here, Vl is 2. from equations (26) and (24).
T...(33) Therefore, by substituting equation (33) into equation (32), we find the transfer function H(ω) of this circuit.

becomes.

On the other hand, the transistor (4) constituting the constant current circuit (60)
8) The base-emitter voltages of (47) and (52) are expressed as V BE4Ei, V BE4
7t-3J: and VBE52. ! l: Then, V BE4
Since B = V BE47 = V BE52, (2
3) From the relationship of the formula, I e4G = I e4? = I e52
--- (35) Here Ie48:) transistor (
46) Emitsuri current Ie47: Transistor (47
) emitter current Ie52: The emitter current of transistor (52) is established, and the current amplification factor of the common base of the transistor is sufficiently close to 1, so Ie4G = Ie47 = 21112 = 2・I3 =
(38) is established.

Similarly, the sum of the emitter currents of transistors (51) and (51a) is the emitter current of transistor (52) I e5
2 and transistors (51), (51a)
The emitter currents of and (54) are equal, and the sum of the emitter currents of transistors (55) and (55a) is equal to the emitter current of transistor (54), that is, Ie52 = 2 m Ie51 = 2 e Ie51a
=2 * Ie54= 4 ・Ie55 = 411
T e55a ... (37) Here Ie51:) Emitter current of transistor (51) Ie51a:) Emitter current of transistor (51a) Ie54:) Emitter current of transistor (54) Ie5
5:) Emitter current Ie55a of transistor (55):
) The emitter current of the transistor (55a) is established.

In addition, the voltage generated when the emitter currents I e55 and I e55a of the transistors (55) and (55a) flow into the resistor (58) with a resistance value R (7) and the base-emitter voltage V BE of the transistor (55)
The sum of 55 is the base-emitter voltages VBE4B and VBE4? of transistors (46) and (47).
Since it is equal to V BE48= V BE47= V B
E55+R (I e55 + I e55a)
-(38) holds true.

Here, I e4B = I e47 = I e52
= 2 bow 2; 2・l3=I, equation (33) uses the relationship of equations (37) and (23), ■ Here, l548:) Saturation radio wave 1s of transistor (46)
55:) This becomes the saturation current of the transistor (55). Therefore, from equation (34), the temperature becomes as follows, and the electrolytic value is proportional to the absolute temperature.

Equation (34) is from equation (4o) This means that the cutoff frequency ωC is and Q is This shows that it is a second-order low-pass filter.

Also, if the resistor (5B) with a resistance value of R is used as a variable resistor external to the IC, the capacitor (36) inside the IC
Even if the capacitance value CL of the capacitor (42) and the capacitance value C of the capacitor (42) vary, the cutoff frequency ωC can be corrected by controlling the resistance value R of the resistor (56).
Although the absolute values of CL and C vary among C, CL,! -C
The ratio of Q between each IC can be considered to be constant.
The variation in can be ignored.

Furthermore, since the values of CL and C do not change with temperature, the filter circuit has good temperature characteristics.

The low-pass filter circuit shown in FIG. 1 is, in principle, an example in which an equivalent inductance circuit is constructed as shown in FIG. 2, and an RLC filter circuit is constructed on both sides. In this Figure 2, (Ia) indicates the input terminal, (44a
) and (45a) both represent variable constant current sources whose flowing current is I/2, and (48a).

(47a) shows a variable constant current source in which the magnitude of the current flowing together is ■. Further, the circuit shown in FIG. 2 can be expressed by an equivalent circuit shown in FIG.

In Figure 3, the resistor (57) is the emitter dynamic resistance of the transistor (39) in Figure 2 and the transistor (40).
(58) is the sum of emitter dynamic resistance of terminal T7
, represents a voltage-controlled radio wave source in which a current gml times the voltage v1 between the terminals 18 flows, where gml is the transformer of the differential amplifier circuit (62) consisting of transistors (37) and (38) in FIG. Indicates conductance. Furthermore (5
9) is the voltage V between the input terminal (Ia) and the output terminal (43)
'fI which is twice gm for L+-Vout! , shows an electronically controlled current source with a falling current, where gm2 is the transistor (27), (28), (29), (30) in FIG.
, (32), (33).

A differential two-stage amplifier circuit (6) consisting of (34) and (35)
In this Figure 3, which shows the transconductance of 1), the input impedance Zin when looking from the input terminal (1a) and the output terminal (43) is, but if the resistance value of the resistor (57) is R1, then・・・
・Since (45) holds true, substituting equation (45) into equation (44) results in...(46), which means that resistor RL is the intestine! "gm2" RI CL, reactance XL is □ and active gml/gr
s2 indicates that the tangent XL is an inductive reactance,
That is, in FIG. 3, it behaves equally as an inductance between the input terminal (Ia) and the output terminal (43).

Therefore, the low-pass filter circuit shown in FIG. 1 can be equally replaced with the circuit shown in FIG. 4. In FIG. 4, (7o) indicates a resistor with a resistance value RL, and (71)
indicates an inductor with an inductance value XL, where R
The values of L and XL are expressed by formula (31).

From equation (40)...(47) From equations (26) and (40), in4 k -T! in4gm2=-
One dispute −−* −= −6・k・TRq6
・R...(48) Furthermore, from equations (28) and (40),...(49) In other words, in the ronnox filter circuit shown in Figure 1, the external resistor is the resistance of the resistor. By changing the value H,
The fill cutoff frequency can be controlled by changing the values of RL and XL.

In addition, in the embodiment shown in FIG. 1, the constant current circuit (60)
The transistors (48), (50), 8 and (53) and the resistor (49) constitute the transistors (51), (
51a).

(52), (54), (55) and (55a) c
7) The controller L/actuator (7) is for determining the DC operating point, and the same effect as the embodiment shown in FIG. 1 can be obtained by using another configuration, for example, the configuration shown in FIG. 5. There is no need to mention what can be said.

In the embodiment shown in FIG. 1, diode-connected transistors (2B) are used as the first and second resistance elements.
, (32) was used, but a resistor may be used instead.

Figure 6 is 1. In the block circuit diagram of an embodiment using a resistor as the second resistance element, (+01) indicates a battery that provides the same DC voltage as the input signal, (28a), (32a)
) and (103) each indicate a resistor with a resistance value of R2, (102) and (105) indicate an npn transistor, and 104) indicates a pnp transistor.

In the figure, the input signal causes a transistor (27).

(29), (30), (33) and resistance (28a)
, the signal current 11 flowing through (32a) is Vin-Vout iI=□...(52)4.
It becomes r e + 2・R2.

Here, from equations (14) and (25), the signal current 1 flowing through the transistors (34) and (35) due to the input signal
2 becomes...(53), and transistors (27), (29), (30)
, (33), (34) (35) and resistance (28a)
, (32a), the transconductance g112 of the differential two-stage amplifier is g+s2 (54).

On the other hand, transistors (27), (29), (30)
The direct current 11 of the emitter current of (33) is the transistor (102), (104), ! : and resistance (, +03) are equal to the second current a'1, and at the same time are equal to the suction current Q by the transistor (+05) that constitutes the constant current circuit.

Therefore, 2・I2 =Il =I...(5
5) holds true.

Therefore, from equations (40) and (55), equation (54) becomes, and the cutoff frequency ωC of this circuit is calculated from the equivalent circuit shown in Fig. 4 and equation (4B)...(57) Also, Q Hato becomes.

In this case, as in the embodiment shown in FIG. 1, the cutoff frequency of the external IC can be changed by changing the resistance value R of the resistor (56). Further, the resistance value R2 varies depending on the temperature, but if the resistance value R2 is made sufficiently smaller than H, the temperature characteristics can be almost ignored.

〔Effect of the invention〕

According to the present invention, passive LRI is implemented within the IC.
Even if the value of '- varies, the inductance value of the 1-equivalent inductance circuit can be adjusted by changing the resistance value of the resistor externally connected to the IC, and at the same time the cutoff frequency can be corrected. Good temperature characteristics. RL
This has the effect of providing a C filter circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing an equivalent inductance circuit of this embodiment, Fig. 3 is an equivalent circuit diagram showing the principle of the equivalent inductance circuit of Fig. 2, and Fig. 4 is a diagram showing an equivalent inductance circuit of this embodiment. The figure is an equivalent circuit diagram of the embodiment shown in Figure 1, Figure 5 is a circuit diagram showing another example of the configuration of the constant 'Wt flow circuit, and Figure 6 shows the main part of another embodiment of the present invention. Block circuit diagram, Fig. 7 is a circuit diagram showing an RLC low-pass filter obtained by synthesizing equivalent inductance using a conventional NIC, Fig. 8
9 is a circuit diagram showing a NIC, FIG. 9 is a circuit diagram configuring a difilator using the NIC, and FIG. 10 is an equivalent circuit diagram showing the difilator of FIG. 9. (1a)...Input terminal, (14)...Power supply terminal which is the first reference potential point, (27)...First polarity terminal
transistors, (28), (28a) - first (7
) resistance element, (:l”l)--second transistor of second polarity, (3o)...third transistor of second polarity, (31)...at third reference point A certain battery, (
32), (32a)...second resistance element, (33)
...Third transistor of first polarity, (34)...
Sixth transistor of first polarity, (35)... Eighth transistor of first polarity, (3B)... Capacitance value is C
(37)...10th transistor of first polarity, (38)...9th transistor of first polarity, (38)...5th transistor of first polarity transistor, (4o)...a seventh transistor of the first polarity, (41)...a battery serving as a fourth reference potential point,
(42)...Second capacitor with a capacitance value of C, (43
)...Output terminal, (44a)...Third variable constant current source, (45a)...Second variable constant current source, (46a)
...first variable constant current source, (47a)...fourth variable constant current source, (56)...variable resistor, (8o)...
... Absolute temperature proportional variable constant current FL circuit, (6I) ... Differential two-stage amplifier circuit, (62) ... Differential amplifier circuit, (63
)...Grounding point which is the second reference potential point, (84)
...Arbitrary reference potential point. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) The input terminal is connected to the base and the collector is the first
The emitter of a first transistor of a first polarity connected to a reference potential point of
A first series body is connected to the emitter of the transistor, and the collector of the second transistor is connected to the second reference potential point, and the base is connected to the third reference potential point, and the output terminal is connected to the base. an emitter of a third transistor of a first polarity connected to and having a collector connected to the first reference point is connected to an emitter of a fourth transistor of a second polarity via a second resistive element; a second series body having a collector connected to the second reference potential point and a base connected to a third reference point of the fourth transistor; and a second series body having a base connected to the fourth reference potential point and the collector is connected to the first reference point, the emitter of the fifth transistor of the first polarity is connected to the collector of the sixth transistor of the first polarity, and the emitter of the sixth transistor is connected to the first variable constant. a third series body connected to the second reference potential point via a current source and whose base is connected to the emitter of the second transistor;
The emitter of a seventh transistor of a first polarity, the base of which is connected to the fourth reference potential point and the collector of which is connected to the first reference potential point, is connected to the collector of an eighth transistor of the first polarity. and a fourth series body in which the emitter of the eighth transistor is connected to the first variable constant current l and the base is connected to the emitter of the fourth transistor. circuit and
a ninth transistor of a first polarity, the collector of which is connected to the first reference potential point via the output terminal and the second variable constant current source, and the base of which is connected to the collector of the sixth transistor; a tenth transistor of a first polarity, whose emitter and collector are respectively connected to the first reference potential point via the input terminal and the third variable constant current source, and whose base is connected to the collector of the eighth transistor; A differential amplifier circuit is connected between the collectors of the sixth and eighth transistors and the emitters of the transistors connected to the second reference potential point via fourth variable constant current sources, respectively. and a second capacitor connected between the output terminal and an arbitrary reference potential point, and the first to fourth variable constant current sources increase and decrease in proportion to the absolute temperature. and the first and fourth
A filter circuit in which the variable constant current source is configured to be variable while maintaining a current value twice that of the second and third variable constant current sources.