JPS6037804A - Local oscillating circuit - Google Patents

Abstract

PURPOSE:To increase the overlapping of the frequency at switching by using a varactor diode in place of a switching diode so as to expand the frequency variable range and attaining the switching through the use of the varactor diode used in the forward direction. CONSTITUTION:A resonator block C is connected with an amplifier block D by a coupling capacitor C1, and a tuning voltage BT is applied to a connecting point between the capacitor C1 and the varactor diode D1 through a high resistance resistor R1. One end of a resonance line L1 is connected to an anode of the diode D1, the other end of the line L1 is grounded through a high resistance value resistor R2 and connected to the anode of the varactor diode D2' through a coupling capacitor C2. A changeover switch S1 is connected to the connecting point between the capacitor C2 and the diode D2', and a bias potential Bs through a high resistance resistor R9 and a ground potential through a high resistance resistor R10 are given switchingly to the connecting point by the switch S1. A changeover switch S2 is connected to the connecting point between the diode D2 and a capacitor C8, and a ground potential and a voltage BT through a high resistance resistor R7 are given switchingly to the connecting point by the switch S2.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a wideband local oscillation circuit in a system using a hetero gain method, such as a television tuner circuit, SHF JT-1 down converter circuit, etc. It is used in circuits.

(Configuration of conventional example and its problems) Line impedance Zin in a distributed constant circuit has characteristic impedance Z. , if the terminal impedance of the line is Z and the line length is t, then it becomes 2π. However, β = lower (), :wavelength) ・・・・−・
(2) In equation (1), when 21e10, Zln-
jZo−βt ・・・・・・・・・・・・(3) 9 The characteristic when normalized at 2° is λ λ λ as shown in Fig. 1, and it is inductive between 0 and -. It changes like capacitance between 1 and 100. A resonant circuit can be constructed by using the line between λ 0 and - 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, B indicates an amplifier block, and the resonator block Block A is connected to amplifier block B via a coupling capacitor C1. D.
is a first external DC potential (hereinafter referred to as a tuning potential) B, a tuning diode (hereinafter referred to as a varactor diode) whose capacitance can be varied, and D2 is conductive to a second external DC potential (hereinafter referred to as a bias potential) B8. , a switch diode capable of switching non-conduction, Ll is a resonant line, one end of which is connected to the anode of the varactor diode D1, the other end of which is connected to the switch diode D2 via a coupling capacitance C2, and is grounded through a high resistance R2. Ru. The connection point between the coupling capacitance C2 and the switch diode D is a high resistance R5.
Bias voltage B8 is applied through. Resonance is caused by the resonance line L1, the capacitance CD1 of the varactor diode D1, the stray capacitance C7 of the circuit, and the capacitance C of the switching diode D2.
D2 and a combined capacitor of a capacitor CfD connected in parallel to the switching diode D2. If this combined capacitance is C, then at the resonance point j' = Zotanl?l -...... - (4)
There is a relationship υ, and the circuit in Figure 2 has this ω. oscillates.

In the resonator block A, the switch diode D2
When is conductive, the resonator is directly grounded through the coupling capacitor C2, and the influence of the capacitor CfD is almost negligible. Therefore, the resonant capacitance is the sum of the tuning capacitance CD1 of the varactor diode D1, the coupling capacitance C11C2, and the stray capacitance Cf including the amplifier pro-B, but the coupling capacitances C1 and C2
uses a large value for the tuning capacitance CD, so the effective combined capacitance C6 is co= cD1+ c(=-...(5
).

On the other hand, when the switch diode D2 becomes non-conductive, the switch diode D2 is grounded through the capacitance CfD, and since the capacitance CfD is extremely small compared to the combined capacitances C1 and C2, it cannot be ignored and the combined capacitance C8 becomes.

Here CfD21 pF, Cf=0.5pFCD1
= 0.7 pF to 6 pF, C8 in equation (5)
The variable range is 1.2 pF to 6.5 pF, and if the resonant line has an impedance of 5oΩ and a line length of 142 mm, the frequency variable range is 900 MHz to 1750 MHz.
It becomes z.

In the case of formula (6), the change in C8 is 0.9 ], pF ~ 1
．． 35pF, 1700MHz ~ 1900M
Obtain a frequency variable range of Hz. Therefore, by making the switch diode D2 conductive and non-conductive using the B8 terminal in Fig. 2, a frequency variable range from 900 MHz to 1900 MUz is attempted to be obtained. Although there are few overlapping frequencies, there is a drawback that discontinuous parts occur in the frequencies due to variations in the elements.

(Object of the Invention) The present invention aims to improve such drawbacks by using a varactor diode in place of the switch diode, expanding the frequency variable range, and switching by using the varactor diode in the forward direction. It is an object of the present invention to provide a local oscillation circuit that increases frequency overlap during switching and does not generate discontinuous portions due to element variations or the like.

(Structure of the Invention) In order to achieve the above object, the present invention includes a first varactor diode (tuning diode) whose capacitance can be varied by a first external DC potential (tuning potential) in a local oscillation circuit, a resonant line, A second varactor diode whose conduction/non-conduction is controlled by a second external DC potential and whose capacitance can be varied by an external DC potential applied to the first varactor diode.
varactor diodes are connected in series to constitute a resonator section, one end of this resonator section is connected to the base or collector of a transistor constituting an amplifier, and the other end is grounded in an alternating current manner. Connect the input terminal of the first changeover switch to the anode side of the varactor diode of
The input terminals of the second changeover switches are connected to the cathode side, and the second external DC potential is applied to one contact of the first changeover switch through a resistor or a choke coil, and the other contact is connected to the resistor or The first external DC potential is applied to one contact of the second changeover switch directly or divided through a resistor or choke coil, and the other contact is grounded. The device is characterized in that when the first and second changeover switches are operated to control conduction/nonconduction of the second varactor diode, the frequency range is changed over. It is possible to increase the frequency overlap at the time of switching, and it is possible to eliminate discontinuous portions caused by element irregularities or the like.

(Description of Embodiment) Hereinafter, an embodiment of the present invention will be described from the beginning with reference to the drawings. FIG. 3 shows the configuration of a local oscillation circuit in one embodiment 1+1 of the present invention. In FIG. 3, block C is a resonator section and block D is a narrow section. The resonator block C is connected to the amplifier circuit D through a coupling capacitor C1, and a tuning voltage BT is applied to the connection point between the coupling capacitor C1 and the varactor diode D1 through a high resistance R1. A resonant line L1 is connected to the anode of the varactor diode I)1.
One end of the resonant line L1 is connected, and the other end of the resonant line L1 is connected to a high resistance R2.
-C is connected to the anode of the varactor diode D2 through the coupling capacitor C2. It's ox.
A specific capacitor C8D is connected in parallel to the varactor diode D'2, and the cathode of the varactor diode D'2 is grounded through the large capacitor C8.

A changeover switch S1 is connected to the connection point between the coupling capacitor C2 and the varactor diode D'2, and the changeover switch S1 connects a bias potential B8 through a high resistance R9 to the connection point, and a grounding through a high resistance R4°. I'm trying to change the way it's given to me. A changeover switch S2 is connected to the connection point of the varactor diode D'2 and the capacitor C8, and the connection point of this changeover switch S2 is connected to the ground, and the tuning voltage BT (or this) is connected through the high resistance R7. ◇The above-mentioned changeover switches S1 and 82 may be independent of each other or may be linked.

In the above configuration, the changeover switch S is now selected.

When the changeover switch S2 is set to the d side and the changeover switch S2 is set to the d side, the varactor diode D2 becomes conductive, and the resonator becomes grounded through the coupling capacitance C2, the large image fACB, and the changeover switch s2. Therefore, the resonant capacitance is the varactor diode D1
The tuning capacitance CD, and the coupling capacitance C1, C2° (C8),
The amplifier is combined with the stray capacitance C8 including RI D, but since C1, C2, and C8 should have large values relative to cDl, the actual coupling capacitance C6 is Co-CD1+Cf...
...-(7) becomes.

Excellent, changeover switch S1. S2 on side b and C
When it is on the side, reverse bias is applied to the varactor diode, and if the capacitance of the varactor diode +D'2 is cl,2.

where CH) = 1 pF, Cf = 0.5 pF
CD, = 0.7 pF ~ 6 pF, CD2=0
．． 5 pF to 5 pF, the variable range of C8 in equation (7) is 1.2 pF to 6.5 pF, which is the same as before, and the resonant line has an impedance of 50 Ω and a line length of 14.2 pF.
If +m++, the frequency Tif change, j, α range is 900
MHz to 1750 MHz.

In the case of formula (8), the change in C8 is 0.98pF to 3.5p
The change ratio of F, Nashi, and Co is 3.6, compared to the conventional 1.5.
(1,35A) 91), the frequency variable jliα range is now 1175 to 18751 (old 2), and the frequency overlap when switching has been increased from 50 MI (7, to 575 MHz). .

Amplifier block D is the amplifier block 13 in the case of FIG.
This amplifier block will be explained here. In FIG. 3, the base of the transistor Q1 constituting the amplifier is connected to the resonator block C via the aforementioned coupling capacitor 3tC1, and the collector of the transistor Q1 is grounded through the large capacitor C6. Further, a bias is applied to the collector of the transistor Q1 through the entire resistor R5, and a base potential is further applied through the resistor R4. In this case, the base bias need not be of the self-feedback type. The emitter-collector capacitance C5 of the transistor Q1 connects the shortest distance between the emitter and the ground in an alternating current manner, and improves the stability of broadband oscillation. R2 is a choke coil that extracts high power. R6 is an emitter resistor, and C
The oscillation output is taken out through 7, and the current is approximately 38 m.
Approximately 10 dBm of air can be extracted at A time. Note that there are various methods for taking out the oscillation output, including a method in which the capacitance of C6 is set to about 10 pF and the output is taken out from the collector, and a method in which the oscillation output is taken out by L or capacitive coupling to the resonant line.

Considering the power, it is best to take it out from the emitter.

In the case of the present invention, there are many ways to take out the output or set the resonant line, but the present invention
By applying a bias voltage to the varactor diode in the resonator section to make it conductive, and then applying a tuning voltage or its divided voltage, the frequency variable range is increased, and as a result, the frequency overlap during switching is increased. This is an important point. Also, the varactor diode D'2
can be the same as or different from the varactor diode D1.

In the resonator block C, the varactor diode D1 is supplied with a reverse bias voltage of the tuning voltage BT, and the varactor diode D'2 is supplied with a tuning voltage B together with the bias voltage BS.
It is important that the voltage T or its divided voltage is applied, and the orientation of the diodes D, D' does not particularly matter. In the above embodiment, R in the resonator block C
1+ R7 and R7 may use choke coils instead of resistors.

(Effects of the Invention) As explained above, the local oscillation circuit of the present invention includes a tuning diode whose capacitance can be varied by a first external DC potential;
A resonator section is constructed by connecting in series a resonant line and a varactor diode whose conduction/non-conduction is controlled by a second external DC potential and whose capacitance can be varied by an external DC potential applied to the tuning diode. , one end of this resonator part is connected to the base or collector of a transistor constituting the amplifier, and the other end is grounded in an alternating current manner, and a first lJJ is connected to the anode side of the varactor diode.
Connecting the input terminal of the changeover switch to the cathode side and the input terminal of the second changeover switch to the cathode side, and applying a second external DC potential to one contact of the first changeover switch through a resistor or a choke coil, The other contact is grounded through a resistor or choke coil, and the first external DC potential is applied to one contact of the second changeover switch through the resistor or choke coil, and the other contact is connected to the ground through the resistor or choke coil. The contacts are grounded and these first
The frequency range is changed by controlling conduction/non-conduction of the glucta diode by operating a second changeover switch.This configuration expands the frequency variable range, and as a result, It is possible to increase the frequency overlap when changing the frequency of the local oscillation circuit by 9 times.

Therefore, according to the present invention, it is possible to eliminate frequency discontinuities due to element variations, etc., and it is possible to provide a highly reliable local oscillation circuit.

[Brief explanation of the drawing]

λ Fig. 1 is an impingance fl'r characteristic diagram of 7 lines terminated on one side, Fig. 2 is a circuit diagram of a conventional example of a local oscillation circuit, and Fig. 3 is a circuit diagram of a local oscillation circuit in an embodiment of the present invention. be. A, C... Resonator part professional, l'3, 1)-
Amplifier block, L, ... resonant line, D, , D'2
Barac tag diode', Ql''h transistor, sl
, s2...Selector switch. Patent applicant Matsushita Electric Industrial Co., Ltd. (-2-) Figure 1-'' × Δ 2 So Entrance 4 2 4 Figure 2 L J Figure 3 L-11111, J

Claims (1)

[Claims] A tuning diode whose capacitance can be varied by a first external DC potential, a resonant line, and a conduction/conduction circuit by a second external DC potential.
A varactor diode whose non-conduction is controlled and whose capacitance can be varied by an external direct current potential applied to the tuning diode is connected in series to constitute a resonator section, and one end of this resonator section constitutes an amplification plate. A first terminal is connected to the base or collector of the transistor, and the other end is grounded in an alternating current manner.
The input terminal of a changeover switch is connected to the cathode side, and the input terminal of a second changeover switch is connected to the cathode side, and the second external DC potential is connected to one contact of the first changeover switch through a resistor or a choke coil. the other contact is grounded through a resistor or a choke coil, and the first external DC potential is applied to one contact of the second changeover switch in the same amount or in divided form through the resistor or choke coil; The other contact is grounded and these first
and a local oscillation circuit characterized in that the frequency range is switched by controlling conduction/non-conduction of the varactor diode by operating a second changeover switch.