JPS58172010A - Capacitive reactance circuit - Google Patents

Abstract

PURPOSE:To obtain capacitive reactance stable against fluctuations of temperature by using the 1st differential amplifier consisting of transistors (TR), a capacitance, and the 1st constant current source and the 2nd differential amplifier which is connected at bases to the 1st differential amplifier and has the 2nd constant current source. CONSTITUTION:A constant current source 13 is connected to the common emitter of the differential amplifying circuit consisting of common emitter TRs 10 and 11, a scamm-capacity capacitor C12 is connected between the collector and base of the TR10, and the current mirror circuit 19 consisting of a TR20 and a diode 21 is connected to the collectors TRs 10 and 11. To the common connection emitter of the differential amplifying circuit 14 consisting of TRs 15 and 16 connected at bases to the TRs 10 and 11 in common, a constant current source 17 is connected; and the TR15 is diode-connected and the current mirror circuit 22 consisting of a TR23 and a diode 24 is connected to the collectors of the TRs 15 and 16. When currents flowing from the current sources 13 and 17 are I and IE respectively, equivalent reactance viewed from a terminal 25 is Cx(I/IE) and a stable reactance circuit irrelevant to fluctuations of temperature is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for isometrically forming a large-capacity IJ actance in an IC (integrated circuit). It is something to do.

The use of ICs in audio equipment, etc. is popular, but inductive reactances such as coils and capacitive reactances such as large capacitors cannot be incorporated into monolithic ICs. It was common to attach

However, for inductive reactance, it is possible to calculate isometric KI using circuit elements such as transistors and resistors that can be easily integrated into ICs.
Technology has been developed to form a large-capacity reactance in a KIC, and there are examples of it being incorporated into an actual KIC, but there are no examples of large-capacity reactance being integrated into an IC.

Incidentally, a capacitive reactance circuit as shown in FIG. 1 has been filed by the same applicant as the present invention. This consists of first and second transistors (1) and (2) whose emitters are commonly connected, and a small-capacity capacitor (3) connected between the collector and base of the first transistor (1) that can be easily converted into a KIC. ), a resistor connected between the bases of the first and second transistors (1) and (2), and a current source connected to a common emitter of the first and second transistors (1) and (2). (5), and can obtain a large capacitance reactance equivalent to one when viewed from the terminal (6). In the circuit shown in Fig. 1, if the voltage at the terminal (6) is ``Os'', the input current is 11, and the current flowing through the capacitor (J is 1), the base voltage EEe1 of the first transistor (1) is
The base voltage of 2) is the reference (R is the resistance value of resistor (4)), and the input current 11 is 11 m・1・gm+12 ……e fist・…
... (2) (where gm is the first transistor (1
) is the mutual conductance of ). By the way, the collector current of the first transistor (1) is generally sufficiently larger than the current flowing through the capacitor (3), so the equation (2) is expressed as 11/1-gm...・・・・・・・・・
・・・・・・・・・・・・＋2) Tonal. Also, the current 12 flowing through the capacitor (3) is II (where C is the capacitive reactance of the capacitor (3),
ω is the angular frequency). Therefore, from equations (1), (2) and (3),
1 input current is 11 rin...
This can be expressed as +41, which means that the circuit shown in Figure 1 has a resistor (7) with a resistance value of 1/gm and a capacitor (8) with a capacitance reactance of R-gm-C, as shown in Figure 2. This shows that it is equivalent to a series circuit of The mutual conductance (gm) in Equation (4) is further expressed as a function of the current flowing in the electric current q+51 as shown in Equation (5).

2 to 7 4kT Therefore, from equation (5), the equivalent capacitance reactance is R'
gm ” C wealth, w T' R” C” engineering...
・・・・・・・・・・・・ (6) becomes current source (5)
It is proportional to the electric current flowing through the area. Therefore, if the current flowing through the current source (5) is changed, the circuit of FIG. 1 becomes a variable capacitance or actance.

As mentioned above, the circuit shown in Figure 1 is convenient because it can obtain equivalent capacitance reactance by using only elements that can be integrated into an IC, increasing the degree of freedom in integrating it into an IC.
Since the term is unstable with respect to temperature, when the circuit shown in the s1 diagram is used as a parallel capacitor of an oscillation element, it has the disadvantage that the oscillation frequency fluctuates.

The present invention has been achieved in the above points, and will be described below based on embodiments and with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which (9) shows first and second transistors αG whose emitters are common and connected.
and aυ, @ is a small capacitor connected between the collector and base of the first transistor terminal, and 1m is the $1 and second transistor fl.
a first current source connected to the common emitter of l and αυ; ) a second differential amplifier circuit consisting of a fourth transistor +II connected to the base of the transistor +II, (lη is a 1l12 current source connected to the common emitter of said third and fourth transistors u9 and u19, (
11 is a constant voltage source for supplying a reference voltage to the bases of the second and fourth transistors α and I19;
) A transistor (to) and a diode (211), a first current mirror circuit for supplying the collector current of the first and second transistors +1 (I and fill, and
is a second current mirror circuit consisting of a PIP transistor (to) and a diode (to) for supplying the collector current of the third and fourth transistors and (]e.

Therefore, in the diagram j83, the junction resistance R1 between the base and emitter of the third transistor 09 is equal to the junction resistance R1 of the second current source 11
If the current of η is xB, then the junction resistance RM between the base and emitter of the fourth transistor α is also as shown in equation (7). Therefore, from the base of the third transistor (to) to the fourth transistor (ls
The equivalent impedance Rz when looking at the base of is, and from equations (6) and (8) above, the equivalent capacitance/actance when looking from the terminal in the circuit of FIG. 5 is as follows. No. 9
) As is clear from the equation, the equivalent capacitance reactance of the circuit shown in Figure 11 IS is the capacitance C of the capacitor α,
It is determined by JIIN, the second current jlU, and the ratio j of current I flowing through a and E, and does not include the crystal element. Therefore, the circuit shown in FIG. 3 is extremely stable with respect to temperature, and is particularly suitable for use in an oscillator.

Furthermore, as is clear from equation (9), the first current source (1 m
If at least one of the current generator E of the second current source 0η and the current generator E of the second current source 0η is made variable by a control signal, the equivalent capacitance reactance can be changed, and the circuit of FIG. 3 can be used as a variable capacitor actance. In particular, by changing the first current source (13), the capacitance reactance can be changed linearly, and like a voltage controlled oscillator, a variable capacitor reactance that is stable and changes linearly with respect to temperature can be used. It becomes extremely easy to integrate the necessary equipment into ICs.

As described above, the IJ actance circuit according to the present invention is suitable for IC implementation and has excellent characteristics that are stable with respect to temperature.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a capacitive reactance circuit which is the basis of the present invention, FIG. 2 is an equivalent circuit diagram thereof, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. Explanation of main drawing numbers (1tl11υ(15[1i9...transistor, α
Hot water...condenser, stop...114th source, αη...
-Second current source.

Claims (2)

[Claims] (1) a first pair of transistors whose emitters are commonly connected; a reta capacitor connected between the collector and base of one of the pair of transistors;
a first current source for determining emitter currents of the pair of transistors; a second pair of transistors each having a base commonly connected to the bases of the pair of transistors; and an emitter current of the second pair of transistors. and a second current source for determining the equivalent capacitance seen from the collector of one of the first pair of transistors, the capacitance of the capacitor and the current ratio of the first and second current sources. A capacitive reactance circuit characterized by being formed as defined by and K. (2) At least one of the first and second current sources is a variable current source whose flowing current changes according to a control signal,
Claim 1, characterized in that a variable equivalent capacitance is obtained according to the current flowing through the variable current source.
Capacitive reactance circuit described in section.