JPH0336444B2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a voltage-controlled LC oscillation circuit used in radio synthesizers, etc., and is designed to be highly stable, compact, and wide-band. It is something.

"Prior Art" Conventionally, as a means of changing the oscillation frequency of an LC oscillation circuit used in a voltage controlled oscillation circuit, as shown in FIG. 4 or FIG. 5, inductance L and capacitance C are used to determine the oscillation frequency. of,
A method is adopted in which the constant of either the inductance L or the capacitance C is changed by connecting to an oscillation support circuit l mainly composed of transistors and FETs, and using switches _S1 ...Sn composed of PIN diodes and transistors. was.

"Problems to be Solved by the Invention" As a means to widen the band by changing the oscillation frequency of an oscillation circuit, as shown in Fig. 4, a capacitance C consisting of parallel capacitances C ₀ , C ₁ . . . Cn is used.
The method of changing the constants using switches S _{1 .} . . Sn increases or decreases the capacitance C as an oscillation frequency determining element, which in turn changes the modulation sensitivity. This means that a problem arises in that the modulation sensitivity changes every time the oscillation frequency of the oscillation circuit is changed. Therefore, a gain control circuit is required to keep the modulation sensitivity constant, making it unsuitable for wideband use. More specifically, when the capacitance C changes in f=1/2π√LC, it directly affects the modulation sensitivity and does not change constantly (for example, as the capacitance C increases, the modulation sensitivity decreases).
There was a problem in that adjustment was required every time the frequency band changed due to switching of the capacitance C.

Instead of changing the capacitance C, the inductance L, which determines the oscillation frequency, can be changed as shown in Figure 5.
The method of changing the constant does not change the modulation sensitivity.
However, unnecessary inductance is connected to the oscillation circuit due to the junction capacitance of the PIN diode or transistor used as a switch when it is off. For example, the inductance Ln is connected to the oscillation circuit by the junction capacitance of the switch Sn. Therefore, there was a problem that parasitic oscillation occurred. Attempting to prevent this parasitic oscillation requires the provision of extra and complex circuitry. Furthermore, since the physical shape of inductance is larger than that of capacitance, there is a problem that the overall shape of the oscillation circuit also becomes larger.

"Means for Solving the Problems" The present invention has been made to solve these conventional problems, and is directed to an LC oscillation circuit formed by connecting an inductance l and a capacitance c as oscillation frequency determining elements. , by keeping the capacitance c constant, dividing the inductance l, and adding a capacitance a in parallel with one of the divided inductances _l1 ,
The oscillation frequency is determined by equivalently varying the _inductance while maintaining the relationship between _the inductance _{l 1} and the capacitance a: It was designed to change the .

"action" The oscillation frequency of the oscillation circuit with l and c is f=1/2π√lc It is expressed as

However, when l is divided into two parts, l1 and l2, the inductance Xl becomes Xl=Xl ₁ +Xl ₂ . By adding the reactance Xa in parallel to Xl ₁ , the inductance Xl becomes Xl=Xl ₂ +−Xl ₁ ·Xa/Xl ₁ −Xa.

Here, −Xl ₁・Xa／Xl ₁ −Xa＞0, |Xl ₁ |<|Xa|
The oscillation frequency is changed by varying the inductance while satisfying the following.

"Embodiment" An embodiment of the present invention will be described below based on the principle diagram of FIG. 1.

1 is an oscillation support circuit mainly composed of transistors, etc., and this oscillation support circuit 1 includes an inductance l and a capacitance c for determining the oscillation frequency.
A parallel circuit with is connected, but the reactance l
is divided into two in series inductances l ₁ and l ₂ (l=
l ₁ + l ₂ ) and further, these inductances l ₁ ,
There is a capacitance a between the connection point of l ₂ and earth.
Add. Here, the inductance l ₁ ,
l ₂ and capacitance a are set to values that satisfy the following relationships: −Xl ₁ ·Xa/Xl ₁ −Xa>0, |Xl ₁ |<|Xa|.

In the above configuration, there is a relationship between the inductance Xl before division and the capacitances Xl ₁ and Xl ₂ after division as Xl = Xl ₁ + Xl ₂ , and since Xl is variable, the capacitance Xa is Due to the addition, Xl=Xl ₂ +−Xl ₁・Xa/Xl ₂ −Xa.

Here, Xl is the reactance value of inductance l, _Xl1 is the reactance value of inductance _l1 , _Xl2 is the reactance value of inductance _l1 , and Xa is the reactance value of capacitance a.

The oscillation frequency f = 1/2π√lc, and in order for this to vary over a wide band, it must be in the inductive range, so −Xl ₁・Xa/Xl ₁ −Xa>0, | The constants are chosen to satisfy the condition Xl ₁ |<|Xa|.

Next, FIG. 2 shows a specific circuit diagram of the present invention, in which 2 is a modulation input terminal, 3 is a modulation input terminal,
is a variable capacitance diode, 4 and 5 are capacitors, and 6 is a variable capacitance diode.
is resistance. Also, multiple capacitances c ₀ ,
c ₁ ... cn are connected in parallel, of which capacitance c ₀ is for fine adjustment, c ₁ ... cn is for band variation to widen the band, and switches s ₁ ... sn consisting of PIN diodes, transistors, etc. inserted in series. 1 is the oscillation support circuit, c is the capacitance,
7 is an oscillation output terminal.

In such a circuit configuration, for example, a switch
When any of s ₁ ...sn is closed, the corresponding frequency characteristics become like the solid line characteristics F ₁ ...Fn in Figure 3. For example, when the switch sn is closed, the fine adjustment capacitance c ₀ is When it is varied, it is varied as shown by the dotted line characteristic Fn'.

"Effects of the Invention" Since the present invention is configured as described above, even if the radio band is divided into multiple parts, the modulation sensitivity of the oscillation circuit follows a certain curve, making it easy to correct.
It is also easy to make strip lines. moreover,
The added capacitance consists of a variable capacitance and a plurality of switchable fixed capacitances coupled in parallel with each other, so if any of the capacitances is selectively coupled, the frequency characteristics corresponding to each can be obtained. , and can be fine-tuned.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the principle of the oscillation circuit according to the present invention, FIG. 2 is an electric circuit diagram showing a specific embodiment of the oscillation circuit according to the present invention, FIG. 3 is a frequency characteristic diagram, and FIGS. FIG. 5 is a conventional circuit diagram. 1...Oscillation support circuit, L, l, _l1 , _l2 ...inductance, c, a...capacitance.

Claims (1)

[Claims] 1. In an LC oscillation circuit formed by connecting an inductance l and a capacitance c as an oscillation frequency determining element, the capacitance c is constant,
The inductance l is divided into _l1 and _l2 , and a capacitance a is added in parallel with one of the divided inductances _l1 , and this capacitance a is
It consists of a variable capacitance and a plurality of selectively switchable fixed capacitances coupled in parallel, and between this capacitance a and the inductance l ₁ , Xl=-Xl ₁・Xa/Xl ₁ −Xa>0, |Xl ₁ |<|Xa| Here, Xl is the reactance value of inductance l, and _Xl1 is _the reactance value of inductance _l1 . An oscillation circuit characterized in that the oscillation frequency of the oscillation circuit is changed by equivalently varying the inductance while maintaining the relationship.