JPS6038903A - Local oscillating circuit - Google Patents

Abstract

PURPOSE:To prevent an oscillated frequency from being changed suddenly against change in the tuning potential by giving two different tuning potentials to two tuning diodes connected in series from one tuning potential. CONSTITUTION:A division potential obtained by dividing a tuning potential BT with resistors R3 and R4 is impressed to a cathode of a tuning diode D2. The tuning potential BT is impressed to a cathode of a tuning diode D1 through a high resistance resistor R1. The resonance capacitance is the combined capacitance of a tuning capacitor CD1 of the D1, a tuning capacitor CD2 of the D2, coupling capacitors C1, C2 and a stray capacitor Cf including an amplifier section block D, and the D2 is selected indentical to the D1, and the division resistors R3, R4 are selected identically R3=R4. Denoted the Cf as 0.5pF, the impedance of the resonance line as 50OMEGA, and the length of line as 15mm., the oscillation frequency f0 to the tuning potential BT is as shown in a fiqure, in which the steep change in the oscillating frequency f0 is suppressed against the change in the tuning potential BT.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a wideband local oscillation circuit in a/stem using a hetero gain method, and is used, for example, in a television tuner circuit or an sHF down converter circuit. It is.

(The configuration of the conventional example and its problems) The line layer impedance 2 in the distributed constant circuit is as follows: the characteristic impedance is 2°, and the terminal impedance of the line is Z.
, if the line length is t, then 2π.

becomes. However, β-7 (λ, wavelength) ... (2) (1
) In the equation, when zR−0, Zin ”' JZotanβt ・−(3),
The characteristic when this is normalized by 2 becomes λ λ λ as shown in Fig. 1, and it changes as inductive between 0 and -, capacitive between 7 and 7, and so on. A resonant circuit can be constructed by using the section between 0 and 0 of this line and adding a capacitance to it.

FIG. 2 shows a conventional example of a local oscillation circuit using such a resonant circuit. That is, this local oscillation circuit is a reflection type oscillator constructed by connecting the above-mentioned resonant circuit to an amplifier. In the figure, A indicates a resonator block and B indicates an amplification block. Dl and D2 are tuning diodes whose capacitances can be varied by an external DC potential, that is, a tuning potential BT.
The combined capacitance CD and the stray capacitance Cf constitute a resonant capacitance. C4 is a large coupling capacitor, and the connection point between this coupling capacitor c1 and the anode of the varactor diode D2 is grounded through a resistor R2. Ll is a resonant line, one end of which is connected to the anode of varactor diode D, and the other end grounded. Resonance occurs between the resonant line L1 and the varactor diodes D and D.
2 and a combined capacitance of the stray capacitance C0 of the circuit. If this combined capacitance is C8, there is a relationship at the resonance point, and the circuit in FIG. 2 has this ω. oscillates.

Tuning potential BT is applied through high resistance R4 to the connection point between the cathode of varactor diode D1 and the cathode of varactor diode D2.

As mentioned above, the resonance capacitance is the tuning capacitance CD1 of the varactor diode D, and the tuning capacitance CD of the varactor diode D2.
2, and the stray capacitance Cf including the coupling capacitance C1 and the amplifier block B. However, C must be a large value for C, C1Dl I)2, so the actual combined capacitance co is: Become.

Here, if the varactor diode D1 and the varactor diode D2 are equivalent, then D4. Since an equal potential is applied to D2 as a tuning potential, CD,=CD2 (6), and the equation (5) becomes.

FIG. 3 shows an example of C-■ characteristics of varactor diodes D1 and D2. Also, in equation (7), C,=0.5(p
F) The capacitance C of varactor diode D1 from Fig. 3
FIG. 4 shows the value of C8 by substituting the value of D1 into equation (7). Furthermore, substitute the value from FIG. 4 for C8 in equation (4), and set the impedance of the resonant line to 50Ω.

Assuming the line length is 15 degrees, equation (4) shows ω. Calculate the oscillation frequency f with respect to the tuning potential BT. Figure 5 shows this.

As can be seen from FIG. 5, in the case of the above-mentioned conventional local oscillation circuit, the oscillation frequency f for a change of tuning potential BT from 0 to 10 (V). The change in tuning potential B is 1° to 20 (V
) has the disadvantage that it is significantly more rapid than the change in

(Objective of the Invention) The present invention aims to improve such drawbacks by dividing the tuning potential BT applied to the cathode of the varactor diode D1 and applying the divided potential to the cathode of the varactor diode D20. For a change, the oscillation frequency f. To provide a local oscillation circuit that can prevent sudden changes in oscillation.

(Structure of the Invention) In order to achieve the above object, the present invention provides a first tuning diode that can vary the capacitance of an external DC potential (tuning potential), a resonant line, and a device that divides the external DC potential (tuning potential). A second tuning diode whose capacitance can be varied depending on the divided potential is connected in series to form a resonant circuit, and this resonant circuit is connected to the base or collector of the transistor forming the amplifier circuit to form a local oscillation circuit. This configuration is characterized in that the oscillation frequency can be prevented from changing abruptly with respect to changes in the external DC potential (tuning potential).

(Description of Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 6 shows the configuration of a local oscillation circuit in one embodiment of the present invention. In FIG. 6, C is a resonator block and D is an amplification block. The resonator block C is connected to the amplification section D through a coupling capacitor C4, and the coupling capacitor C1
A connection point between the anode of the varactor diode D2 and the anode of the varactor diode D2 is grounded through a resistor R2. A coupling capacitor C2 is connected to the cathode of the varactor diode D2, and a divided potential obtained by dividing the tuning potential B7 by resistors R6 and R4 is applied to the connection point thereof.

The cathode of varactor diode D is connected to the cathode of varactor diode D2 through coupling capacitance c2, and D
, and 02 through a high resistance R7. The anode of Varacta Dimate D1 has
One end of the resonant line L1 is connected, and the other end of the resonant line L1 is grounded.

The resonance capacitance is the tuning capacitance CDI of the varactor diode D, the tuning capacitance cD2 of the varactor diode D2, and the coupling capacitance C.
1, C2 and the stray capacitance C2 including the booster block D, where C1+C2 is cD.

Since a large value is used for CD2, the actual coupling capacitance C6 is as follows.

The c-■ characteristic of the varactor diode D1 is the same as that shown in FIG. 3 above, and here the varactor diode D2 is assumed to be equivalent to , and the dividing resistor R3 of the tuning potential BT shown in FIG. , R4 is, for example, R3:R4=1:1, and the potential applied to the cathode of the varactor diode D2 is always the tuning potential BT, then the tuning capacitance of the varactor diode D2 and the tuning potential BT at that time are: The relationship is as shown in Figure 7.

In equation (8), Cf=o, 5[pF], and the third
From FIG. 7, the varactor diode D1. Tuning potential B of D2.

Fig. 8 shows the results obtained by calculating the values for each and substituting them into equation (8), and subtracting the value of co.

Here, by substituting the value from FIG. 8 into C8 of equation (4), the impedance of the resonant line is 5oΩ, fgA path length is 15t
ω from equation (4) as mn. Calculate the oscillation frequency f with respect to the tuning potential BT. The results are shown in Figure 9.

FIG. 9 and the oscillation frequency f for the tuning potential BT of the conventional example.

As can be seen by comparing FIG. 5, which shows the change in the oscillation frequency f, with respect to the change in the tuning potential BT, by using the present invention. It is possible to suppress sudden changes in

Next, the amplifier units P O and D will be explained. A transistor forming an amplifier in FIG. .

The resonator block C is connected to the base of the resonator block C via the aforementioned coupling capacitor C4, and the collector is grounded through the large capacitor C4. Further, a bias is applied to the collector through a resistor R6, and a base potential is further applied through a resistor R5. In this case, the base bias need not be of the self-feedback type. The capacitance C3 between the emitter and collector of the transistor Q1 is to ground the shortest distance between the emitter and the ground in an alternating current manner, and C3 improves the stability of broadband oscillation. This is a choke coil that removes the L2id high temperature. R7 is an emitter resistor and C
It outputs an oscillation output through 5 and 9, and the current is about 38 mA.
At times, it can emit about 10 dBm of gas.

There are various ways to extract the oscillation output, and C
It is also possible to set the capacitance of 4 to about 10 pF and take it out from the collector, or to take it out to the resonant line by L or capacitive coupling.

Considering the power, it is optimal to output 9 from the emitter. There are many methods for setting the output and the resonant line, but in the present invention, two tuning diodes connected in series can be tuned from the same tuning potential to different tuning potentials. An important point is that by providing .

(Effects of the Invention) As explained above, the present invention includes a first tuning diode whose capacitance can be varied by a tuning potential, a resonant line, and a second tuning diode whose capacitance can be varied by dividing the tuning potential and varying the capacitance by the divided potential. By connecting the tuning diode in series to form a resonant circuit, and connecting this resonant circuit to the base or collector of the transistor that makes up the amplifier circuit to form a local oscillator circuit, it is possible to change the tuning potential as usual. This is designed to suppress rapid changes in the oscillation frequency.

Therefore, according to the present invention, it is possible to provide a local oscillation circuit with excellent tuning voltage-oscillation frequency characteristics.

[Brief explanation of the drawing]

λ Figure 1 is an impedance characteristic diagram of a 7-line with one side termination,
Figure 2 is a circuit diagram of a conventional example of a local oscillation circuit, Figure 3 is a CV characteristic diagram of a tuning diode, Figure 4 is a CV% characteristic diagram of a tuning capacitance of a conventional example, and Figure 5 is a diagram of a local oscillation circuit. A characteristic diagram of tuning voltage versus oscillation frequency of a conventional example of the circuit, FIG. 6 is a circuit diagram of a local oscillation circuit in an embodiment of the present invention, and FIG. 7 is a tuning diode D2 of the local oscillation circuit in an embodiment of the present invention. FIG. 8 is a characteristic diagram of tuning capacitance versus tuning potential of a local oscillation circuit in an embodiment of the present invention, and FIG. 9 is a characteristic diagram of tuning capacitance versus tuning potential of a local oscillation circuit in an embodiment of the present invention. FIG. 3 is a characteristic diagram of voltage versus oscillation frequency. A, C...resonant block, B, D...amplifier block, Ll...resonant line, Dl, D2...varactor diode, Q,...transistor. Patent applicant: Matsushita Electric Industrial Co., Ltd. ---1 Agent: Kouji Hoshino (h) Figure 1 Figure 2 s, Eave Figure 6 Figure 3 BT Figure 4 Figure 5 Figure 7 BT Figure 8 Figure 9

Claims (1)

[Claims] The first capacitance can be varied by external DC potential (tuning potential).
a tuning diode, a resonant line, and the external DC potential (
A second tuning diode whose capacitance can be varied by dividing the tuning potential) is connected in series to form a resonant circuit, which is connected to the base or collector of the transistor making up this resonant circuit. local oscillation circuit.