JPH0716132B2 - Local oscillator circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner circuit, a local oscillator circuit used in an indoor unit of a CATV converter or a satellite broadcast receiver.

2. Description of the Related Art In recent years, due to the spread of CATV and the need for multi-channel reception of television tuners, after converting the input signal to an intermediate frequency of a frequency higher than the received signal and passing through a narrow bandpass filter, The up-down tuner used to convert to the second intermediate frequency or the CATV converter has been widely used. The characteristic of this method is that the oscillation frequency of the local oscillator can be changed in the high part of 1 GHz or more. Therefore, it is possible to receive multiple channels with a simple configuration.

A conventional local oscillation circuit will be described below with reference to the drawings. FIG. 7 shows a conventional example.
Reference numeral 71 is an amplification transistor, 72 is a resonance circuit, 73 is an AC component removal circuit, 74 is a current source type amplification circuit, terminal 7A is a tuning voltage supply terminal, and 7B is a power supply terminal. FIG. 8 is a detailed block diagram of FIG. 7, where 81,811 are NPN transistors, 89,84,812 are coupling capacitors, 83,85,810 are bias resistors,
87 indicates a resonance line. 88 is an AC component removal filter, terminal 8A shows a tuning voltage supply terminal, and terminal 8B shows a power supply terminal. The part surrounded by the broken line shows the correspondence with FIG. 7.

The operation of the local oscillator configured as described above will be described below.

The collector of the amplifying transistor 71 is grounded by the capacitor 82, and the impedance seen from the base is negative. If the resonance circuit 72 is connected to this base via the coupling capacitance 84, the sum of the impedance seen by the resonance circuit and the negative impedance of the above base has a gain of 1 or more and a phase characteristic of 2nπ (rad) [ It oscillates at a frequency such that n = 0,1,2, .... The emitter of the transistor 81 is DC-coupled to the constant current source type amplifier 74 via the AC removal filter 73, and in terms of AC, it oscillates from the emitter of the transistor 81 to the base of the transistor 81 via the coupling capacitor 812. Is supplied, amplified, and an oscillation output signal is obtained from the terminal 8C via the coupling capacitor 89.

Problems to be Solved by the Invention However, in the configuration as described above, the oscillation transistor 81 and the amplification transistor 811 must always be used with the same current, and the optimum conditions of each transistor differ depending on the current. In this case, there was a drawback that either performance could not be maximized.

In view of the above-mentioned problems, the present invention provides means for using both the oscillation transistor and the amplification transistor under optimum conditions.

Means for Solving the Problems In order to solve the above problems, the local oscillator of the present invention is
The collector of the amplifying transistor is grounded AC, and the base of the collector is connected to the resonance circuit.
The collector of the constant current source type amplification transistor is connected through the AC component removal filter that removes the alternating current component, and the AC is connected to the base of the constant current source type amplification transistor through the coupling capacitance, and the output signal is collected. While taking it out from
A current shunt circuit is connected to the collector of the constant current source type amplifying transistor so as to draw or add a current so as to satisfy the optimum use condition of the above two transistors.

Action The present invention has the above-described configuration, if the optimum operating point for the current of the oscillation transistor (mainly f _T or h _fe ) is smaller than the operating point of the constant current source type amplifying transistor as a current value, By flowing a current into the collector of the constant current source type amplification transistor, and if it is the other way around, it is possible to operate each transistor at the optimum point.

Embodiment A local oscillator circuit according to an embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG.

FIG. 2 shows a block diagram of the local oscillator in the first embodiment of the present invention. In FIG. 2, 11 is a transistor for amplification (oscillation transistor), 12 is a resonance circuit,
13 is an alternating current removal circuit, 14 is a constant current source type amplifier, 15 is a current shunt circuit, terminal 1A is a tuning voltage supply terminal, 1B is a power supply terminal,
1C indicates an oscillation output terminal. FIG. 1 shows a specific example of FIG. 21,211 is NPN transistor, 2
Reference numerals 9, 24, 212 are coupling capacitors, 23, 25, 210 are bias resistors, 27 is a resonance line, 28 is a choke coil for removing an AC component, and 15 is a current shunt circuit shown in FIG.
The one for discharging the current is shown in FIGS. 3 and 4, and the one for absorbing the current is shown in FIGS. 5 and 6, respectively. Fig. 3 shows the connection between the power supply V _CC and the collector of the transistor 211 by the resistor 31, and Fig. 4 shows the connection between the power supply V _CC and the collector of the transistor 211, the PNP transistor 41, the diode 42 and the resistor. This is a known constant current circuit composed of 43 and 43. Figure 5 shows transistor 21
A resistor 51 is inserted between the collector of 1 and the ground. FIG. 6 shows a constant current circuit composed of an NPN transistor 61, a diode 62 and a resistor 63 between the collector of the transistor 211 and the ground.

The operation of the local oscillator circuit configured as described above will be described below with reference to FIGS. 1 to 6. 1 and 2, the amplifying transistor 11, the resonance circuit 12, the AC removal circuit 13, the constant current source type amplifier 14, the tuning voltage supply terminal
The blocks up to 1A, the power supply terminal 1B, and the oscillation output terminal 1C are the same as the operation described in the conventional example, and the description will be omitted to avoid duplication. In this configuration, when the current shunt circuit 15 is installed and the optimum operating current of the amplifying transistor 21 is smaller than the operating current of the constant current source type amplifier 14, the difference current is set to the constant current of FIG. 3 or FIG. Made with a circuit,
This is supplied to the collector of the constant current source type transistor 211, and conversely, when the optimum operating current of the amplifying transistor 21 is larger than the operating current of the constant current source type amplifier 14, FIG. The constant current circuit shown in FIG. 6 draws out a constant current from the collector of the constant current source type transistor 211 to enable optimum operation. In addition,
The output terminal of the current shunt circuit 15 may be connected to the emitter of the amplification transistor 21.

As described above, according to the present invention, the current shunting circuit is installed in the emitter of the oscillation amplifying transistor or the collector of the constant current source type amplifying transistor to operate the two transistors at the optimum operating current value. Therefore, the performance can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a local oscillator circuit according to an embodiment of the present invention, FIG. 2 is a block diagram thereof, and FIGS. 3 to 6 show specific circuit examples of a current shunt circuit according to an embodiment of the present invention. Circuit diagram, FIG. 7 is a block diagram showing a configuration of a conventional example, and FIG. 8 is a circuit diagram showing a specific example thereof. 11 …… (for oscillation) amplification transistor, 12 …… Resonance circuit,
13: AC component removal circuit, 14: Constant current source type amplification circuit, 15
...... Current shunt circuit, 21 …… Oscillation transistor, 211…
… Constant current source type amplification transistor.

Claims (1)

[Claims] 1. A resonance circuit, in which a collector of an oscillating transistor is grounded by a capacitance, and a variable capacitance diode whose capacitance value is varied by an external variable potential and a resonance line are arranged in series is connected to the base of the oscillation circuit. The other end is grounded in an alternating current, a variable potential from the outside is applied to the cathode of the variable capacitance diode, a higher potential than the base emitter is applied to the collector of the oscillation transistor, and an impedance for removing the alternating current component is applied to the emitter. A load is applied, an oscillation signal is taken out from the emitter, the collector of the first constant current transistor is connected to the other end of the AC component removing impedance load, and the oscillation output signal is connected to the base via a coupling capacitor. Supply, ground the emitter, give a bias potential to the base, take out the amplified signal from the collector, and remove the AC component In at least one of the impedance loads, a current shunt circuit is provided so that a current corresponding to the difference between the optimum operating currents of the two transistors is drained when the optimum operating current of the oscillation transistor is large and is added when the optimum operating current is small. Local oscillator circuit.