JPH07131243A - Voltage-controlled oscillator - Google Patents

Abstract

PURPOSE:To obtain the voltage-controlled oscillator which can stably oscillate even at high frequencies without being affected by the stray capacity of the external terminal of an integrated circuit by providing the integrated circuit equipped with a transistor(TR) having one end of an inductance connected to its base. CONSTITUTION:The inductance L and a capacitor C1 are incorporated in the integrated circuit and formed on a semiconductor substrate. The stray capacity of the external terminal P2 is present in parallel to a varicap diode Cv, the capacity value of the varicap diode Cv is variable, so the influence of the stray capacity is adjustable. Further, the stray capacity of the external terminal P3 is present in parallel to a capacitor C2, but the capacity value of the capacitor C2 can optionally be selected, so it can be set to a proper value in consideration of the influence of the stray capacity. The inductor L is constituted on the semiconductor substrate, so no stray capacity is present at the base of the TR Q. Further, the influence of the external terminal can be absorbed by adjusting the varicap diode Cv and capacitor C2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator capable of high frequency oscillation.

[0002]

2. Description of the Related Art In recent years, blocks that handle high frequencies in the 2 GHz band, such as the frequency converter of a BS tuner, are being integrated into circuits. Conventionally, as a voltage controlled oscillator as a local oscillator used for frequency conversion, a Clap oscillation circuit is often used in terms of stability of oscillation, and is configured as shown in FIG.

In FIG. 3, 1 is a resonance circuit that determines the oscillation frequency, L is the inductance that constitutes the resonance circuit, and C
v is a varicap diode that constitutes a resonance circuit, R1
Is a resistor, Vt is a voltage source for applying a tuning voltage to the varicap diode, C3 is a capacitor for blocking direct current, C1, C2 are capacitors for increasing the negative resistance of the oscillator, 2 is an integrated circuit, P1, P2, P3 and P4 are external terminals of the integrated circuit, Q is a transistor, R2, R3 and R4 are resistors for biasing the transistor, and Vcc is a voltage source for biasing the transistor.

When the DC bias element is omitted in FIG. 3 and replaced with an AC equivalent circuit, the result is as shown in FIG. The voltage sources Vt, Vcc and the capacitor C3 are short-circuited, and the resistor R
1, R2, R3 and R4 are opened. Stray capacitance exists between the external terminals of the integrated circuit. Since a large number of GND terminals are arranged in the high frequency integrated circuit, the stray capacitance existing between the GND terminals is large, and it is necessary to take special consideration.
In FIG. 4, stray capacitances associated between the external terminals P2 and P3 and GND are indicated by CP2 and CP3.

The operation of the voltage-controlled oscillator configured as described above will be described below. The oscillation frequency is changed by changing the DC voltage applied to the varicap diode Cv to change the capacitance value. As an oscillation condition, it is necessary that a negative resistance be obtained when the transistor Q side is seen from the inductance L, in other words, a reflection coefficient is larger than 1. The values of the capacitors C1 and C2 are set so that the negative resistance of the oscillator is sufficiently obtained, but when oscillating at a high frequency of 1 GHz or more, they are set to a value of about 1 pF.

[0006]

However, in the above conventional configuration, the stray capacitances CP2 and CP3 of the external terminals have a great influence on the negative resistance of the oscillator. Stray capacitance is usually 1
Since it exists near pF and has a value that cannot be ignored as compared with the capacitors C1 and C2, it lowers the negative resistance of the oscillator and causes oscillation stop.

In particular, the stray capacitance CP2 is associated with the base of the transistor Q, which is an amplifying element, so that its influence is great.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a voltage-controlled oscillator which can be stably oscillated even at a high frequency without being affected by the stray capacitance of the external terminal of the integrated circuit. To do.

[0009]

In order to achieve this object, a voltage controlled oscillator according to the present invention is an integrated circuit having a transistor in which one end of an inductance is connected to a base and a semiconductor substrate in which the inductance is formed. Equipped with
Inside the integrated circuit, the other end of the inductance is connected to an external terminal of the integrated circuit, and further, outside the integrated circuit, a varicap diode is connected to the external terminal. .

[0010]

With this configuration, since the base of the transistor is not directly connected to the external terminal, the stray capacitance of the external terminal does not affect the negative resistance of the oscillator, and sufficient oscillation stability can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a voltage controlled oscillator according to an embodiment of the present invention. In FIG. 1, 1 is a resonance circuit that determines the oscillation frequency, L is an inductance that forms the resonance circuit, and Cv
Is a varicap diode that constitutes a resonance circuit, R1
Is a resistor, Vt is a voltage source for applying a tuning voltage to the varicap diode, C3 is a capacitor for blocking direct current, C1, C2 are capacitors for increasing the negative resistance of the oscillator, Q is a transistor, R2, R3. , R4 is a resistor for biasing a transistor, 2 is an integrated circuit, P1, P2,
P3 and P4 are external terminals of the integrated circuit, Vcc is a voltage source for biasing the transistor, and these are the same as in the conventional example. The difference from the conventional example is that the inductance L and the capacitor C1 are incorporated in an integrated circuit and formed on a semiconductor substrate. On the semiconductor substrate, metal such as aluminum is used for internal wiring to couple the elements, and an inductance can be formed by using this internal wiring.

When the DC bias element is omitted in FIG. 1 and replaced with an AC equivalent circuit, the result is as shown in FIG. The voltage sources Vt, Vcc and the capacitor C3 are short-circuited, and the resistor R
1, R2, R3 and R4 are opened. Further, in FIG. 2, stray capacitances associated with the external terminals P2 and P3 are shown as CP2 and C2.
This is indicated by P3. Unlike the conventional example, the base of the transistor Q has no stray capacitance.

The operation of the voltage controlled oscillator configured as described above will be described below. The oscillation frequency is changed by changing the DC voltage applied to the varicap diode Cv and changing the capacitance value. Although the stray capacitance CP2 of the external terminal P2 exists in parallel with the varicap diode Cv, since the capacitance value of the varicap diode Cv can be changed, the influence of the stray capacitance CP2 can be adjusted. As an oscillation condition, it is necessary that a negative resistance be obtained when the transistor Q side is seen from the inductance L, in other words, a reflection coefficient is larger than 1. The values of the capacitors C2 and C3 are set so that the negative resistance of the oscillator is sufficiently obtained. External terminal P3
Stray capacitance CP3 exists in parallel with the capacitor C2,
Since the capacitance value of the capacitor C2 can be arbitrarily selected, it can be set to an appropriate value including the influence of the stray capacitance CP3.

As described above, according to this embodiment, since the inductance L is formed on the semiconductor substrate, the base of the transistor Q has no stray capacitance. Further, the influence of the stray capacitances CP2 and CP3 of the external terminals can be absorbed by adjusting the varicap diode Cv and the capacitor C2. Therefore, it is possible to sufficiently obtain the negative resistance required as the oscillation condition.

In this embodiment, the capacitor C1 is formed on the semiconductor substrate, but the base of the transistor Q
Since there is a diffusion capacitance between the emitters, the capacitor C1
Is not always necessary. Further, the external terminal P3 may be eliminated by forming the capacitor C2 on the semiconductor substrate.

[0016]

As described above, in the voltage controlled oscillator according to the present invention, since the inductance of the resonance circuit is formed on the semiconductor substrate, there is no stray capacitance in the base of the transistor, so that a sufficient negative voltage is obtained even at a high frequency of 1 GHz or more. It is possible to obtain the effect that the sexual resistance can be obtained and stable oscillation can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a voltage controlled oscillator according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an AC equivalent circuit of the voltage controlled oscillator.

FIG. 3 is a diagram showing an example of a circuit of a conventional voltage controlled oscillator.

FIG. 4 is a diagram showing an example of the AC equivalent circuit of FIG.

[Explanation of symbols]

 1 Resonant Circuit 2 Integrated Circuit Cv Varicap Diode L Inductance Q Transistor Vt, Vcc Voltage Source CP2, CP3 Stray Capacitance C1, C2, C3 Capacitor R1, R2, R3, R4 Resistor P1, P2, P3, P4 External Terminal of Integrated Circuit

Claims (1)

[Claims] 1. An integrated circuit comprising: a transistor having a base to which one end of an inductance is connected; and a semiconductor substrate on which the inductance is formed. Inside the integrated circuit, the other end of the inductance is outside the integrated circuit. A voltage-controlled oscillator which is connected to a terminal and further has a varicap diode connected to the external terminal outside the integrated circuit.