JPS6229209A - Local oscillation circuit - Google Patents

Abstract

PURPOSE:To improve the reliability of the titled circuit by changing a base potential of an oscillation amplification transistor (TR) so as to expand the variable range and to suppress the current change of the TR at changeover of the base potential. CONSTITUTION:A power voltage is given to an oscillation amplifier circuit 11 from a terminal Vcc and connected to a current source shared amplifier 15 via a DC system path. An AC rejection filter 14 is connected to the DC system path to cut off the AC component. A constant current circuit is added to the emitter of the oscillation TR Q1 to suppress the current fluctuation and the base potential of the oscillation TR Q1 is increased to decrease the potential difference with the collector potential thereby increasing a Cob (reverse bias capacitance) and the oscillation frequency is moved lower totally. Further, the output of the TR Q1 is amplified by using the constant current circuit to obtain the amplified output without increasing the circuit power.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a local oscillation circuit used in a television tuner circuit, an ATV converter, or an indoor unit of a satellite broadcast receiver.Prior Art In recent years, ATVs have become popular. Due to the need for multi-channel reception by television tuners, the input signal is converted to an intermediate frequency higher than the received signal, passed through a narrowband bandpass filter, and then converted to a second intermediate frequency for use. Up-down tuners or cA'1'y converters have come into widespread use. The feature of this system is that the oscillation frequency of the local oscillator is varied in a high range of IG) 12 or higher, so that multi-channel reception is possible with a simple configuration.

A conventional local oscillation device will be described below with reference to the drawings. FIG. 4 is a diagram showing a conventional example, and in the figure,
41 is an oscillation amplifier, 42 is a resonant circuit, 43 is an amplifier,
Reference numeral 44 indicates a switching means for switching the variable range of the oscillation frequency. In the figure, an amplifier 41 and a resonant circuit 42 constitute a local oscillator, and the oscillation frequency is changed by an externally tuned DC potential. The oscillation output is amplified by a circuit 4.
3, and supplies it to an external circuit from an output terminal 4C. The amplifier circuit 43 is still used as a buffer with external circuits, and the oscillation amplifier 41. This improves the stability of the oscillation circuit composed of the resonant circuit 42.

The specific configuration of FIG. 4 is shown in FIG. The blocks surrounded by broken lines in the figure are described in correspondence with the blocks in FIG. 4. The oscillation amplifier 41 utilizes the fact that when the collector of the transistor Q1 is grounded in an alternating current manner through the bypass capacitor C1, the impedance seen from the base of the transistor Q1 becomes negative, and the oscillation amplifier 41 generates a Furthermore, by grounding the transistor Q1 in an AC manner through a series oscillator circuit consisting of a varicap D1 whose capacitance can be varied according to an external DC potential, a resonant inductance L1, and an internal capacitance viewed from the base input side of the transistor Q1. The negative gain seen from the base side of the transistor Q1 and the loss of the resonator are canceled, and the sum of the phase characteristics seen from the base side of the transistor Q1 and the phase characteristics of the resonator is 2nr (n==o, 1
．． 2,3. ...--) oscillates at a frequency of raa. This oscillation frequency can be adjusted by changing the tuning potential (DC) applied from terminal 4B.
By changing the capacitance of the resonator, the amplitude of the impedance of the resonator 9
Since the phase characteristics change, the frequency that satisfies the excavation conditions also changes, and the oscillation frequency also changes. The resonant capacitance is the parallel sum of the capacitance of the varicap D1 and the stray capacitance of the circuit, and the series sum of the input capacitance of the oscillation transistor Q1 (mainly the reverse bias capacitance 11cob between the base and collector), so the variable range of the oscillator is is mainly limited by the Cob of the oscillation transistor Q1. Therefore, in the conventional circuit, taking advantage of this, the base potential of the oscillating transistor Q1 is switched via the resistor R5 by an external switching potential (DC) input to the four terminals. That is, when the potentials of the four terminals become high, the pace potential of the transistor Q1 increases, and the current flowing through the transistor Q1 increases. The GOb of the transistor Q1 increases as the collector current increases, and since current is supplied to the collector of the transistor Q1 from the power supply 'ice through the resistor R2, the GOb of the transistor Q1 increases as the collector current increases.
As the collector potential of υ decreases, the reverse bias voltage between the base and collector also decreases, so Cob acts in the direction of further increase. As mentioned above, as Cob increases, the capacitance value inserted in series in the resonant circuit increases, so the oscillation frequency shifts to a lower level overall, compared to when this method is not used. This had the advantage of being able to expand the lower part of the variable range. (For FIIJ, JP-A-69-1
(See Publication No. 49405) Problems to be Solved by the Invention By the way, there were two problems in the conventional technology. One is that when the switching potential shown in FIGS. 4 and 6 is set to a high potential, the current flowing through the oscillation transistor Q1 shown in FIGS. In many cases, the permissible pc for an oscillation transistor was exceeded. The second drawback is that since the amplifier 43 shown in FIGS. 4 and 5 is used, a current of about 15iIIA is required, which increases the power consumption of the entire circuit.

The present invention solves the problems of the conventional inventions, and has a simple structure that minimizes the overall increase in current even when the external switching potential is set to a high potential. This provides a local oscillation circuit that can

Means for Solving the Problems The local oscillation circuit of the present invention has a resonant circuit added to a common emitter type oscillation transistor base, and a common emitter type transistor having constant current characteristics on the emitter side of the common emitter type transistor. Connect the collector of the amplifier and insert an AC component removal filter, supply the oscillation output from the common emitter transistor to the base of the common emitter amplifier, obtain the amplified signal from the collector, and connect the common emitter transistor to the base of the common emitter amplifier. By having a means to switch the pace potential of the type transistor, it is possible to maintain a constant current while suppressing an increase in the current (power) of the circuit.

Operation The local oscillation circuit of the present invention is capable of suppressing current fluctuations even when the base potential of the oscillation transistor is changed by adding a constant current rotation circuit to the emitter side of the oscillation transistor. By increasing the base potential of the transistor and reducing the potential difference between it and the collector potential, Cob can be increased and the same effect as the conventional example can be obtained. In addition, by separating the constant current circuit and the oscillation transistor in AC terms and amplifying the output of the oscillation transistor using the constant current circuit, the amplified output can be used without increasing the power of the circuit. It is something that can be obtained.

Embodiment A local oscillation circuit according to an embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 2, the oscillation amplifier circuit 11
A resonant circuit 12 and an external switching means 13 are connected to the resonant circuit 12, and a tuning voltage (from terminal 1B) is applied to the resonant circuit 12, so that the resonant frequency of the circuit constituted by the resonant circuit 12 and the oscillation amplifier circuit 11 is set. is changing. On the other hand, a switching potential is applied to the external switching means 13 from the terminal 1, and depending on the magnitude of the switching potential, the base of the oscillation amplifier circuit 11 is changed.

Change the potential between the collectors. The oscillation amplifier circuit 11 is supplied with a power supply voltage from a Vcc terminal, and is connected to a current source shared amplifier 16 via a DC path. An AC removal filter 14 is connected to the DC path to block AC components. The AC output of the oscillation amplifier circuit 11 is applied to the AC input terminal of the current source shared amplifier 16 through an AC signal path, and is amplified, so that an amplified oscillation output signal can be obtained from the terminal 1C.

FIG. 1 shows FIG. 2 in more detail, and the blocks surrounded by broken lines in the figure are shown in correspondence with FIG. 2. The oscillation amplifier circuit 11 makes the impedance of the transistor Q1 negative when viewed from the pace side by grounding the collector of the transistor Q1 with a large capacitor C1.The base of the transistor Q1 has a bypass capacitor. A resonant circuit consisting of a Paris cap D1 and a resonant line L1 is inserted in series via C2, and the other end is grounded. A resistor R is connected to the cathode of the Paris cap D1.
A tuning potential is applied from terminal 1B via 2.

On the other hand, a bias is applied from the base and collector of the oscillation amplifying transistor Q1 by a bias resistor R1, and an external switching potential is applied from one switching terminal via a resistor R4 and a diode D2. In the column shown, only when the switching potential becomes a high potential, transistor Q1
However, if the direction of the diode D2 is reversed, the base potential of the transistor Q1 can be lowered only when the switching potential is a low potential, and if the diode D2 is omitted, The base potential of transistor Q1 can be changed depending on the level of the switching potential. Therefore, you can choose any one. A coil L2 for removing high frequency components is connected to the emitter of the transistor Q1. Resistance R
3, the capacitor C4 constituting the AC removal filter
is connected, whereby the high frequency component is removed and the DC component is supplied to the collector of the amplification transistor Q2 constituting the current source shared amplifier 15 via the high frequency removal coil L3. Vcc is applied to the base of transistor Q2.
A voltage divided by resistors R5 and R6 (power source) is applied, and by grounding the emitter of transistor Q2, a constant DC power source is provided. On the other hand, transistor Q1
An oscillation output signal is supplied from the emitter of the transistor Q2 to the base of the transistor Q2 via the coupling capacitor C5. Transistor Q2 amplifies this and connects the collector with multi-coupling capacitance C.
5 to supply the oscillation output signal to an external load. Due to this constant current effect, even if the base potential of transistor Q1 is slightly fluctuated, experiments show that transistor Q
If the present invention is not used, the current flowing through 1 is 20 m →
The 4 ohm current has been reduced from 20 ohm to about 24 mA. The P and C of the transistor will not be exceeded, and the circuit operation will become more stable due to the increase in COb.

FIG. 3 shows another column of the current source shared amplifier 15 in FIG. 1, in which the bias source is a self-bias type, and the bias of the transistor Q2 is connected from the collector to the resistor R5+R.
The voltage is supplied by applying a divided potential of 6 to the base of the transistor Q2. If this is done, the constant current effect will be a little worse, but the difference from FIG. 2 is only a few mA, and there is no problem in practical use.

Effects of the Invention As described above, the local oscillation circuit of the present invention can change Cob, which constitutes the resonance element of the oscillation frequency, by changing the base potential of the oscillation amplification transistor, thereby expanding the variable range. In addition, it is possible to suppress the change in the current of the transistor when switching the base potential, and it is possible to significantly improve the reliability of the circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a local oscillation circuit according to an embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a circuit diagram of a main part of a second embodiment of the present invention. FIG. 4 is a configuration diagram of a conventional local oscillation circuit, and FIG. 5 is a circuit diagram showing a specific conventional array. 11...Oscillation amplifier circuit, 12...Resonance circuit, 13...External switching means, 14...
...AC removal filter, 15...Current source shared amplifier, 1 person...Switching potential input terminal, 1B...
...Tuning potential input terminal, 1C...Oscillation output terminal, Ql...Transistor for oscillation amplification, Q2
...Amplifying transistor that constitutes a constant current circuit, Dl... Varicap diode.

Claims (4)

[Claims] (1) The collector of the oscillation transistor is grounded through a capacitor, and the base is connected to a resonant circuit in which a varicap diode whose capacitance value is varied by an external variable potential and a resonant line are arranged in series. The end of the varicap diode is grounded in an alternating current manner, a variable potential is applied from the outside to the cathode of the varicap diode, and a means capable of varying the base potential is connected to the base of the oscillation transistor.
An impedance load for high frequency rejection is connected to the emitter to extract the oscillation signal, and a filter for high frequency rejection is inserted between the other end of the impedance load for high frequency rejection and ground, and this high frequency rejection filter is inserted between the other end of the impedance load for high frequency rejection. A local oscillation circuit characterized by connecting a constant current circuit through an impedance load. (2) Claim 1, characterized in that a resistor or a resistor and a diode connected in series are used as means for changing the base potential of the oscillation transistor.
Local oscillation circuit described in section. (3) As a constant current circuit, the emitter of the NPN transistor is AC grounded, a constant potential is applied to the base, and the emitter path of the oscillation transistor is connected to the collector via a choke coil, and the oscillation output signal is Supplied via a coupling capacitor to the base of the transistor that constitutes the constant current circuit,
2. The local oscillation circuit according to claim 1, wherein the amplified output is obtained from the collector. (4) The local oscillation circuit according to claim 3, wherein the base potential of the constant current circuit transistor is provided by dividing the collector potential by resistance.