JPS60261209A - Ic-converted stable resistance circuit - Google Patents

Abstract

PURPOSE:To obtain a resistance which is not influenced by a variation portion of an IC internal resistance by connecting a buffer amplifier between an input and an output, in a circuit constituted so as to obtain a current being proportional to a potential difference between two points. CONSTITUTION:A voltage of a point P1 and a voltage of a point P2 are inputted to an operation amplifier 50 in which an input impedance, an output impdedance, and a gain are 2(R+re),<infinity>, and (gm), respectively, so that an output can be obtained from point P3, P4. According to this circuit constitution, the circuit whose gain (gm) is not influenced by a dispersion of an internal resistance of an Ic is obtained. However, when it remains as it is, it does not become a resistance, therefore, ideal buffers 51, 52 are connected between the input and output points P1, P3, and between P2, P4, respectively. As a result, a current (i)=gmX(potential difference between P1, P2) being proportional to the potential difference between the points P1, P2 flows in from the point P3, and flows out of the point P4. In this way, even if a dispersion is generated in the intenal resistance of the IC, a stable IC-converted resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an integrated circuit stabilizing resistor circuit suitable for use as a resistor when an active filter consisting of a resistor and a capacitor is built into a monolithic IC.

BACKGROUND ART AND PROBLEMS When constructing a CR active filter using a monolithic IC, the absolute value of the internal resistance R of rc varies greatly, and the temperature characteristics are very poor, so a stable resistance must be 1-!
For this reason, it is usually necessary to use an external resistor-based current source to cancel out variations in internal resistance.

FIG. 1 shows an example of such a CR active filter, in which (], + (2) (31 and (4)) are current sources using external resistances.

This filter consists of resistance bones (
) and capacitors (13) to (15
), a low-pass filter is applied to the input signal from the input terminal (16), a band-pass filter is applied to the input signal from the input terminal (17), and a band-pass filter is applied to the input signal from the input terminal (17).
For the input signal from IB), each of them functions as a bypass filter.

In this case, the emitter currents of transistors (5) to (8) are determined by current sources (1) to (4) using external resistors, so
It is possible to cancel the change in resistance of the diodes (9) to (12).

However, when the power supply voltage Vcc is 5V, the dynamic range is connected to the emitter side of transistors (5) to (8). The maximum allowable input level is determined by the resistance of the diodes (9) to (12), and the maximum allowable input level is no more than 200 to 300 mV p-p. For this reason, when extracting a desired signal from an input that contains a large amount of unnecessary signals, such as with a low-pass filter after the FM luminance signal demodulation circuit of a VTR reproduction system, the S/N ratio is poor due to the narrow dynamic range. As a result, it has been virtually impossible to implement a CR active filter into an IC.

In other words, in order to create a monolithic IC, it is sufficient to obtain a resistor that is stabilized.

Purpose of the Invention In view of the above points, it is an object of the present invention to realize a stabilized IC resistor that is free from the effects of temperature characteristics and variations.

SUMMARY OF THE INVENTION This invention detects the potential difference between a first point and a second point using a high impedance, and obtains a current proportional to the potential difference at a third point and a fourth point. When the resistance changes, the potential difference between the first point and the second point does not change, and an external resistor is used as a current source for a circuit that outputs a current proportional to the potential difference, and the third point A buffer amplifier is connected between the and the first point and/or between the fourth point and the second point, and a resistor is connected between the third and fourth points that is not affected by the variation in the internal resistance of the IC. This is an IC stabilized resistor circuit designed to obtain the following characteristics.

EXAMPLES Hereinafter, some examples of the present invention will be described with reference to the drawings.

Prior to a detailed explanation of the present invention, a detailed explanation of the present invention will be given.

FIG. 2 is an example of a constant resistance circuit. In other words, the change in the voltage ■ applied to the input terminal (19) and the change in the voltage ■ applied to the input terminal (19)
This is a circuit in which the change in the current I flowing from 19) is proportional. Now, if the voltage between the base and emitter of transistors (20) and (21) is VB2, and the value of the resistor (22) connected between these transistors (20) and (21) is R, then this resistor (22) Since a voltage of -2VBE will be applied to the current, the current will be as follows. Therefore, the impedance Z of this circuit remains constant even if the voltage V and the current (2) change. In other words, . Therefore, this circuit can be represented isometrically as shown in FIG. 3 when viewed from the input terminal (19).

If this resistance value R is the resistance inside the IC, then the above value is also 1
As shown, the variation is about 20%, and the temperature characteristic is 2000pp.
m/deg. Therefore, it is necessary to avoid dependence on these variations and temperature characteristics.

FIG. 4 shows a circuit that uses a current source based on an external resistor so as to be independent of variations in internal resistance of an IC and temperature characteristics.

That is, the voltage VA at the first point (31) and the second point (3
2) voltage VB and the internal resistances (33) and (34) of the IC.
) through transistors (35) and (36), respectively.
Immediately feed the base. The emitters of the transistors (35) and (36) are connected in common, and the connection point is grounded via a current source (37) formed by an external resistor. Also,
A current source (3
8) and (39) are provided respectively. Furthermore, the bases of transistors (35) and (36) are connected to diodes (4o
) and (41), respectively, and the connection point of the mutual cathodes of diodes (4o) and (41) is grounded via a current source (42) based on the internal resistance of the IC.

In this circuit, by applying voltages VA and VB, currents Iy and 12 flowing to the third point (43) and fourth point (44) to which the collectors of transistors (35) and (36) are connected, respectively, are calculated. Ru.

Here, the current source (37) is a constant current source determined by the external resistance Rx, and its value is 2■, and the current sources (38), (39), and (42) are constant current sources determined by the internal resistance RI. And the values are J and 2J, and it is assumed that

For example, if VA=VB, the current IR flowing through the resistors (33) and (34) is IR=O, and the base voltages of the transistors (35) and (36) are set to vc and VB.
If D, then VC=VD=VA=VB,
The same current J flows through the diodes (4o) and (41). Therefore, the current 1y=Iz=■ is the third and fourth
flows to points (43) and (44). At this time, even if the internal resistance R (resistances (33) and (34)) and RI change at the same time (these resistances change in the same way because they are internal resistances of the IC), the transistor (35) and Since the base voltages VC and VD of (36) are still equal, the output currents 1y and Iz do not change.

Next, when voltage VA≠VB, the potential difference VA-
Output currents 1y and Iz are obtained according to VB, but at this time, even if the internal resistance changes at the same time, the potential difference VA-VB does not change, so the currents 1y and Iz do not change.

This can be explained quantitatively as follows.

First, the gain G1 for converting the potential difference VA-VB to the potential difference VC-VN is: (3) (r6 is the emitter resistance of the diodes (40) and (41)) Also, the output current from the potential difference VC-VD The conversion gain gw+ to Iy and Iz is (r+- is the emitter resistance of transistors (35) and (36)) Therefore, from the input potential difference VA-VB, the output current 1y,
The conversion gains g+a and gl+ to Iz are given by the above (31(
4) From the formula, it becomes.

In equation (5), since the emitter resistances re and ri are inversely proportional to the currents J and (2), equation (5) can be rewritten as follows from equation (11, (21).

As is clear from equation (6), when the resistance inside the IC changes by a factor of m, the internal resistance R1 in the denominator becomes mR1, and on the other hand, the internal resistance in the numerator (R
B), so they are canceled out in the end, and gta is not affected by variations in the absolute value of the resistance within the IC.

If the above operation is idealized and written, it can be expressed as shown in FIG. Here, the input impedance of the operational amplifier (50) having the configuration as shown in FIG. 4 is 2 (R+re
), the output impedance is ■.

The gain is gva. The input impedance is affected by variations in internal resistance, but the gain gw+ is not affected by it.

As a result of the above, 2 points P1. Detect the potential difference between P2 with high impedance and generate a current 1out proportional to the potential difference Vin
=gIIl·Vin to point P3. Although a current source circuit output from P4 whose gain gva is not affected by variations in the internal resistance of the IC can be obtained, it does not become a resistor as it is.

In this element as shown in FIG. 5, ideal buffers (5 pieces) and (52) are connected between input and output points I'd and P3 and between P2 and P2, respectively, as shown in No. 6 vgJ. When connected between P4, point P
3 + P 4 is the 7th floor! 1/ as shown in lJ
It becomes equivalent to the resistance of g w. That is, points PL, P2
Current i=gm proportional to potential difference VPt VF6
This is because (VPt-VF6) flows in from point P3 and comes out from point P4.

Note that point P1. The buffer (51) between P3 may not be provided.

At this time, as a by-product, point P3. The potential of P4 can be obtained with low impedance.

As described above, even if variations occur in the internal resistance of the IC, a stable IC resistor can be obtained.

According to this IC-based resistor, the dynamic range can be significantly expanded compared to conventional resistors.

In other words, the resistor circuit in Figure 6 is a transistor.

If expressed in terms of a diode, a resistor, and a current source, it will be as shown in FIG. Here, if each connection point is indicated by A to H as shown in the figure, the dynamic range can be explained as follows.

Now, the minimum voltage at which the current source can operate is VN for an NPN transistor and a PNP transistor, respectively.

vllll, when the voltages at points A and H swing in the same phase, the voltages at points A-H all swing with the same amplitude.

However, point C-F is lower than points A and B by VBE', and points G and H are 2VB lower than points A and B! 'Only low.

Therefore, as is clear from FIG. 9, point A.

The maximum amplitude of B is Vcc-Vl) -VN2VBE (Vp-p)
becomes. Here, Vp = VH = 0.5 (V), Vc
If c=5 (V) and VBE-0,'7 (V), the dynamic range is 2.6 (V p-p ).

Therefore, if an IC filter is constructed using this IC resistor circuit, a sufficient dynamic range can be ensured.

Next, some embodiments in which this resistor is applied to active filters will be described.

Capacitor C and resistor 1/g as shown in Figure 10
A first-order bypass filter consisting of m can be constructed as shown in FIG. 11 to form I and C. in this case,
The input terminal (8(h) and the output terminal (9(h)) are completely equivalent in impedance to those terminals (601) and (,7(h)) of the original circuit.
) is equipped with a buffer, which is convenient for connection with subsequent circuits.

A first-order low-pass filter as shown in FIG.
It can be configured as an IC as shown in FIGS. 3 and 14.

In the case of the configuration shown in FIG. 13, both the input impedance and the output impedance are completely equivalent to the original circuit.

In the case of the configuration shown in FIG. 14, only the input impedance is not equivalent to the original circuit. However, when this circuit is driven by a voltage source, the frequency characteristics and gain are equivalent to the original circuit.

Next, the second-order low-pass filter as shown in FIG. 15 can be configured as shown in FIG. 16 and integrated into an IC.
The secondary bypass filter as shown in FIG. 7 can be configured as shown in FIG. 18 and implemented as an IC.

Conventionally, these secondary filters could not be integrated into ICs due to variations in resistors R1 and R2.

The second-order low-pass filter and 2 in FIGS. 16 and 18
FIGS. 19 and 20 show circuit diagrams of the next bypass filter expressed using transistors, diodes, resistors, and current sources as shown in FIG. In the figure, the current source indicated by Φ is a current source using an external resistance, and the symbol ■ is a current source using an internal resistance.

Application Example The IC resistor circuit of the present invention can be used not only as a filter as described above, but also as an attenuator, since the resistance value changes by changing the current value of the current source using an external resistor. In addition, it can be used for various other purposes.

Effects of the Invention According to the present invention, an IC using a current source using an external resistor
It is possible to obtain a stable IC resistor that is not affected by variations in the absolute value of internal resistance. Furthermore, since this resistor has a relatively wide dynamic range, it can be used satisfactorily even when the power supply voltage is as low as 5V.

In particular, if it is used as a resistor in a CR active filter, it becomes possible to integrate the filter into an IC, and because of its wide dynamic range, it can be used as a low-pass filter in the latter stage of the FM luminance signal demodulation circuit of the VTR playback system as mentioned at the beginning. This is very suitable for extracting a desired signal from an input that contains a large amount of unnecessary signals, such as in the case of

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an example of a conventional CR active filter, Figures 2 and 3 are diagrams for explaining a constant resistance circuit, and Figure 4 is an example of a current source circuit that is the premise of this inventive circuit. , FIG. 5 is an equivalent circuit diagram when the operation of FIG. 4 is idealized, FIG. 6 is a diagram showing an example of the circuit of this invention, FIG. A circuit diagram showing the circuit in Figure 6 in a different way, Figure 9 is a diagram for explaining the effect,
Figures 10, 12, 15, and 17 are diagrams showing examples of the original circuits of CR active filters, Figure 11, Figure 1
3, 14, 16, and 18 are diagrams showing an example of a case in which these original circuits are configured as a filter using a resistor circuit according to the present invention, and FIG. 19 is a diagram showing an example in which the circuit in FIG. FIG. 20 is a diagram showing an example of a circuit diagram using elements such as transistors, and FIG. 20 is a diagram showing an example of a circuit diagram using elements such as transistors. Pl and P2 are the first and second points, P3 and P4 are the third
The fourth point (50) is a circuit that obtains a current output proportional to the potential difference between the two points PL and P2, and (51) and (52) are buffer amplifiers with a gain of 1. μ Benny ut. Same Hidemori Matsukuma'1 so...1: ・j-Pa Figure 9↑A0

Claims (1)

[Claims] The potential difference between the first point and the second point is detected with high impedance, and a current proportional to the potential difference is obtained at the third and fourth points, and when the internal resistance of the IC changes, the above-mentioned The potential difference between the first point and the second point does not change, and an external resistor is used as a current source for a circuit that outputs a current proportional to the potential difference, and the potential difference between the third point and the first point is and/or an IC in which a buffer amplifier is connected between the fourth point and the second point to obtain a resistance between the third and fourth points that is not affected by fluctuations in the internal resistance of the IC. Stable resistance circuit.