JPH0666583B2 - High C / N oscillator circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-frequency oscillator circuit, and more particularly to an oscillator circuit suitable for a VCO of a PLL such as a wireless telephone device.

(Prior Art) An example of a high-frequency oscillator circuit is shown in FIG. Circuit of FIG. 2 is a variant Colpitts oscillation circuit, the oscillation frequency, L _1, C
The series circuit of ₁ is inductive, and the parallel circuit of L ₂ and C ₃ is capacitive. C ₅ grounds the collector of the transistor TR 1 at high frequency, and C ₆ couples the oscillation output to the next stage.

In such an oscillator circuit, C / N is deteriorated by a low frequency noise component generated inside the transistor TR1 or induced on the input side (base side). Means that have been conventionally adopted to draw a high C / N ratio include (1) use of a high Q element as a tuning element (2) increase the operating current of an active element such as a transistor (3) base of a transistor There was a choke coil attached to the.

(Problems to be Solved by the Invention) However, it is difficult to reduce the size of a circuit by means of increasing the diameter of a high-Q element, especially an air-core coil, or inserting a core or attaching a choke coil. Passing a current is problematic in terms of low current consumption and cost.

(Means for Solving the Problems) In order to solve these problems, the present invention provides a high-frequency oscillation circuit, a resistor inserted in a part of an output-side circuit of an amplification element forming the high-frequency oscillation circuit, and the resistor. Connected in parallel to the capacitor to bypass the high-frequency oscillation frequency component to obtain a low-frequency noise component, an input terminal connected to the capacitor, and an output terminal connected to the input side circuit of the amplification element.
A low-frequency amplifier circuit that has an F (low-pass filter), amplifies the noise component obtained by the capacitor, and outputs a phase-inverted signal is provided. An example of C / N conversion is described below, and examples will be described in detail with reference to the drawings.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which the present invention is applied to the conventional example of FIG.

Reference numeral 1 is a low-frequency amplifier circuit that serves as an LPF, C _{1 to} C ₆ are fixed capacitors, L ₁ and L ₂ are coils, R _{1 to} R ₃ are fixed resistors, and TR 1 is a transistor.

In the figure, if the emitter current caused by the noise component generated in the noise component and a transistor internal induced in the base side of the TR1 and i _1, the voltage of the noise component of the output i ₁ R ₃
Becomes

However And f ₁ is the frequency of the noise component. Here, if the gain of the low frequency amplifier circuit 1 is G and the input impedance of the noise component of TR1 is sufficiently larger than R ₁ and R ₂ , the noise component output to TR1 The voltage is Becomes

here If G is made large so that the phase of the input and output of the low frequency amplifier circuit 1 is inverted, the current of the noise component of TR1 is changed by the current of the noise component output from the low frequency amplifier circuit 1. It is canceled out and the current of the noise component of TR1 equivalently stops flowing. However, NF at the low frequency of the low frequency amplifier circuit 1 is sufficiently small. As a result, the oscillation circuit has a good C / N.

Also, at the oscillation frequency f ₀ (Output impedance at low frequency amplifier circuit 1 at f ₀ +
R ₂ ) >> (TR1 input impedance at f ₀ ), C ₄
>> C _3, because that is the (low frequency amplification circuit gain at f ₀ of 1) <1, the low-frequency amplifier circuit which is added to the C / N improving _{1, C 4, R 2,} R 3 is The oscillation frequency f ₀ has almost no effect. Further, the low-frequency amplifier circuit 1 only needs to amplify the low-frequency component and its power is very small, so that its current consumption is small and can be ignored.

Not limited to this embodiment, the present invention can be applied to other types of oscillation circuits by designing the LPF so as not to affect high-frequency oscillation.

Further, if a part or all of C ₁ , C _3, etc. are constructed by variable capacitance diodes, they can be used as a VCO.

(Effect of the Invention) As described above, since the improvement of C / N can be formed by the semiconductor circuit, the IC including the oscillation circuit can be realized. Therefore, a compact, low current consumption, low cost, high C / N oscillator circuit can be realized. Further, since the DC signal is also fed back, the bias is also stabilized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a conventional example. 1 ...... low frequency amplifying circuit, C ₁ -C ₄ ...... fixed capacitor,
L ₁ , L ₂ …… High frequency coil, R _{1 to} R ₄ …… Fixed resistance, TR 1 ……
Transistor.

Claims (1)

[Claims] 1. A high frequency oscillating circuit, wherein a resistor inserted in a part of an output side circuit of an amplifying element which constitutes the high frequency oscillating circuit and a resistor connected in parallel to the resistor to oscillate a high frequency oscillating frequency component. A low frequency noise component, and an input end connected to the capacitor and an output end connected to the input side circuit of the amplifying element and having an LPF (low pass filter) to amplify the noise component obtained by the capacitor. A high C / N oscillating circuit provided with a low frequency amplifying circuit for outputting a phase-inverted signal.