JPH0138989Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Technical field This invention relates to a reactance circuit.
In particular, it relates to a reactance circuit that can generate a negative equivalent reactance and is suitable for integration into an IC (integrated circuit).

(b) Technical background Voltage (current) controlled oscillator circuit (VCO) that can change the oscillation frequency according to the control signal
There is. The VCO generally changes the oscillation frequency by controlling the charging and discharging time of the capacitor, but has the disadvantage that the free run frequency is unstable due to variations and temperature changes.
However, if a stable device such as a crystal resonator is used as the reference oscillation element of the VCO, it has the disadvantage that it is difficult to change the oscillation frequency in accordance with the control signal.

(c) Main points of the invention This invention was created in view of the above points.
The present invention aims to provide a reactance circuit that can be easily integrated into an IC and operates as a negative equivalent reactance suitable for changing the oscillation frequency of a VCO.

(d) Embodiment FIG. 1 shows an embodiment of the present invention, in which 1 and 2 are first and second transistors whose emitters are commonly connected, and 3 is the first and second transistor 1.
and a variable current source connected to the common emitters of the two;
4 is a current mirror circuit consisting of a diode 5 and a transistor 6 connected to the collectors of the first and second transistors 1 and 2; 7 is an output terminal connected to the collector of the first transistor 1; 8;
is a capacitor connected between the output terminal and the base of the second transistor 2, and 9 is a resistor connected between the bases of the first and second transistors 1 and 2.

Now, if the voltage at the output terminal 7 is e ₀ and the current flowing through the capacitor 8 is i ₁ , then the voltage e ₀ and the current i ₁ have a phase difference of 90 degrees, and with respect to the voltage e ₀ , , a current _i1 with a phase shift of 90 degrees flows from the capacitor 8 to the resistor 9. At that time, the base voltage e ₁ of the second transistor 2 is e ₁ =R・i ₁ ...(1) (where R is the resistance value of the resistor 9), and the collector current of the second transistor 2 is
i ₂ is i ₂ = e ₁ · g _n ...(2) (where g _n is mutual conductance). Furthermore, since the first and second transistors 1 and 2 are differentially connected, if the collector current _i2 of the second transistor 2 is as shown in equation (2), the first
The collector current i ₃ of the transistor 1 is i ₃ =−e ₁ ·g _n (3). By the way, the current i ₁ flowing through the capacitor 8 is i ₁ = _e 0 /R+1/jwc...(4) (where c is the reactance w of the capacitor 8)
is the angular frequency), and the current i ₄ flowing to the output terminal 7 is i ₄ = i ₁ + i ₃ ...(5), and assuming that i ₁ ≪ i ₃ , From equation (5), i ₄ =−R·g _n e ₀ /R+1/jwc = e ₀ /−1/g _n +1/j (−wcRg _n ) (6). Therefore, as is clear from equation (6), the first
When the circuit shown in the figure is viewed from the output terminal 7, it is equivalently converted into a series circuit of a resistor with a resistance value of -1/g _n and a capacitor with a reactance of -C.R.g _n . If -1/g _n is small, the circuit in Figure 1 can be regarded as a circuit with negative equivalent reactance. For example, set the resistance value of resistor 9 to 1k.
Ω, the reactance of capacitor 8 is 10 pF, and the mutual conductance is 1/50, the equivalent reactance is as large as -200 pF.The fact that such a large reactance with negative polarity can be integrated into an IC is shown in Figure 1. This is a major feature of reactance circuits.

Further, mutual conductance (g _n ) is expressed by the following equation.

g _n = αqI / 4kT × 2 = α / 52I ... (7) (where, k is Boltzmann's constant, T is absolute temperature, q is the amount of electron charge, α is the current amplification factor, and I is the current flowing through the variable current source 3). Therefore, if the current I flowing through the variable current source 3 is changed, the mutual conductance (g _n ) will change, and the equivalent reactance will also change. Therefore, by changing the current I, the reactance circuit shown in FIG. can be used as a variable reactance circuit.

FIG. 2 shows an example in which the reactance circuit according to the present invention is connected to an oscillator, where 10 is a differential oscillation circuit, and 11 is a reference for a crystal oscillator or the like for determining the oscillation frequency of the oscillation circuit 10. The oscillation element and 12 are reactance circuits according to the present invention. Therefore, if the parallel resonance frequency of the reference oscillation element 11 is ₀ and the collector current of the current source transistor 13 is zero, the oscillation circuit 10 is oscillating at ₀ (free-run oscillation state). At this time, since the operation of the reference oscillation element 11 is extremely stable, the oscillation frequency ₀ does not fluctuate.

Next, when a control signal is applied to the control signal input terminal 14 and collector current I flows through the current source transistor 13, the equivalent reactance X of the reactance circuit 12 is: X=-1/52C・R・α・I... (8) becomes. Therefore, the reactance X is connected in parallel to the reference oscillation element 11, and the overall reactance becomes small. As a result, the parallel resonance frequency increases to ₁ as shown in FIG. 3, and the oscillation frequency of the oscillation circuit 10 also increases. The reactance X is
Since it changes depending on the current flowing through the variable current source 13, by changing the magnitude of the control signal applied to the control input terminal 14, the oscillation frequency of the circuit shown in FIG. 2 can be changed. can be used as a VCO. Therefore, the circuit shown in Figure 2 is
If used as the VCO of a PLL circuit and configured to apply the error signal from the phase comparator to the control input terminal, a PLL circuit with a stable free run frequency and a wide control range can be obtained.

(e) Effects As described above, the present invention has the advantage that a negative equivalent reactance can be obtained by integrating it into an IC. Furthermore, if the reactance circuit according to the present invention is used in an oscillation circuit and the equivalent reactance of the reactance circuit is varied according to a control signal, the oscillation frequency can be varied stably and over a wide range.
We can provide VCO.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a circuit diagram when the present invention is applied to a VCO, and FIG. 3 is a characteristic diagram for explaining the present invention. Explanation of main figure numbers, 1, 2...transistor, 7
...Output terminal, 8...Capacitor, 9...Resistor.

Claims (1)

[Scope of utility model registration request] first and second transistors whose emitters are commonly connected; an output terminal connected to the collector of the first transistor; a reactance element connected between the output terminal and the base of the second transistor; a current source connected to the common emitters of the first and second transistors, and a resistor connected between the bases of the first and second transistors, configured to generate a negative equivalent reactance at the output terminal. A reactance circuit characterized by: