JP4432224B2 - Oscillator and communication device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oscillator used in a high-frequency circuit and a communication apparatus provided with the same.
[0002]
[Prior art]
Conventionally, an oscillator in a microwave band or the like is configured by a Colpitts oscillation circuit or a modified oscillation circuit thereof.
[0003]
FIG. 5 shows a configuration example of a conventional oscillator. In FIG. 5, Q1 is an oscillation transistor, a capacitor C1 is connected between its base and emitter, a collector is grounded at high frequency by a capacitor C7, a capacitor C6 is connected between the emitter and ground, and a base is also provided. A Colpitts type oscillation circuit is configured by providing a resonance circuit between the ground and the ground, and providing an inductive circuit in a portion shown as the resonance circuit.
[0004]
In FIG. 5, Q2 is a buffer transistor, and an oscillation signal output from the emitter of the transistor Q1 is supplied to the base of Q2 via the capacitor C2.
[0005]
[Problems to be solved by the invention]
In such a conventional oscillator, a voltage dividing circuit including resistors R1, R2, and R3 is provided as a base bias circuit for the oscillation transistor Q1, and an output voltage at a connection point between the resistors R2 and R3 is applied to the base of Q1. The output voltage at the connection point between R1 and R2 is applied to the base of Q2.
[0006]
When such an oscillation circuit is used in a mobile communication device such as a mobile phone, how to suppress the overall power consumption is one of the design points. Conventionally, in order to reduce the overall current consumption without reducing the output level, the current (bleeder current) flowing through the resistance voltage dividing circuit (R1, R2, R3 in FIG. 5) for supplying the base bias is as much as possible. It was designed to suppress. That is, generally, if the resistance dividing ratio by R1, R2, and R3 in FIG. 5 is made constant and the series combined resistance value of R1, R2, and R3 is increased, the power consumption by the resistor dividing circuit can be suppressed accordingly.
[0007]
However, as the resistance value of the resistance voltage dividing circuit is increased, the base bias current to the oscillation transistor Q1 is not sufficiently supplied, and the oscillation output level is lowered or the base bias becomes unstable. There arises a problem that the C / N characteristics deteriorate.
[0008]
An object of the present invention is to provide an oscillation circuit, which eliminates the above-described conventional problems by suppressing power consumption by a resistor voltage divider circuit constituting a base bias circuit of a transistor as much as possible and supplying a necessary base current. It is to provide a communication apparatus provided with the same.
[0009]
[Means for Solving the Problems]
In the present invention, a resonance circuit is connected to the first transistor for oscillation, a resistance voltage dividing circuit is connected between the power supply and the ground, and an output of the resistance voltage dividing circuit is connected to the base of the second transistor. The emitter of the second transistor is connected to the base of the first transistor, the collectors of the first and second transistors are connected to the power source, and the emitter current of the second transistor is used as the base bias current of the first transistor. Supply as.
[0010]
As described above, the base bias current of the first transistor for oscillation is supplied as the emitter current from the collector side of the second transistor, and the collector current of the second transistor is a current amplification factor times that of the base current. Therefore, even if the base current supplied to the second transistor is sufficiently small, the necessary base bias current for the first transistor can be supplied. Therefore, the series resistance value of the resistor bias circuit for supplying the base bias with respect to the second transistor is set high, thereby suppressing the power consumption by the resistor voltage divider circuit to be extremely small.
[0011]
In the present invention, at least a resistor is connected between the base of the first transistor and the ground, and the emitter of the first transistor is connected to the base of the second transistor via a capacitor. With this configuration, the output signal from the emitter of the first transistor, which is an oscillation transistor, is fed back to the base of the second transistor, and under a high current amplification factor due to the Darlington connection between the first and second transistors. The input impedance of the amplifier circuit composed of the first and second transistors is made higher. This increases the stability of the oscillation operation.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the oscillator according to the first embodiment will be described with reference to FIGS. In FIG. 1, Q1 is a first transistor that is an oscillation transistor, and its collector is grounded at high frequency by a bypass capacitor C5. The circuits are connected to each other, and a capacitor C2 is connected between the emitter and the base via the base-emitter of Q2, thereby constituting the main part of the Colpitts type oscillation circuit.
[0013]
In FIG. 1, Q2 is a second transistor, and its emitter is connected to the base of Q1. A resistance voltage dividing circuit using resistors R1 and R2 is connected between the power source Vcc and the ground, and the divided voltage output is supplied to the base of Q2. The collectors of Q1 and Q2 are connected to each other so that the power supply Vcc is supplied. A resistor R4 is connected between the emitter of Q1 and the ground, a capacitor C2 is connected between the emitter and the base of Q2, and an oscillation output signal is taken out from the base of Q2 via the capacitor C4. A capacitor C3 between the base of Q2 and the ground is provided to cut high frequency components.
[0014]
In FIG. 1, the base bias current of the oscillation transistor Q1 is supplied from the emitter of Q2, and this current corresponds to (base current of Q2 × current amplification factor of Q2). Since the current amplification factor of Q2 is usually several tens to several hundreds, the current supplied to the base of Q2 from the resistance voltage dividing circuit by R1 and R2 can be kept extremely small. Therefore, the series resistance value of R1 and R2 can be set high without reducing the output level or the C / N characteristic, and the bleeder current by the resistance voltage dividing circuit of R1 and R2 can be made sufficiently small. Thus, the power consumption of the entire oscillator can be reduced.
[0015]
Further, in the example shown in FIG. 1, the oscillation output signal from the emitter of Q1 is fed back to the base of Q2 via the capacitor C2, thereby utilizing the high combined current amplification factor by Q1 and Q2 and from the resonance circuit. It is possible to increase the input impedance of Q1. Therefore, the oscillation operation is further stabilized and the C / N characteristic is improved without being affected by the fluctuation of the impedance of the circuit connected to the oscillator.
[0016]
FIG. 2 is a diagram showing the configuration of the resonant circuit portion shown in FIG. Here, L1 is an inductive element such as a strip line or a chip inductor, and VD is a variable capacitance diode whose electrostatic capacity changes depending on the applied voltage. L2 is an inductive element such as a strip line or a chip inductor, and is configured to apply a control voltage to the variable capacitance diode VD via the inductive element L2. At this time, the capacitor C12 grounds the high frequency component so as not to affect the oscillation frequency. The reactance of this resonance circuit is determined by the inductance of L1, the capacitance of the variable capacitance diode VD, and the capacitances of the other capacitors C10, C11, and C13. The resonance is caused by these values and the capacitances of the capacitors C2 and C6 shown in FIG. The frequency is determined and oscillates at the resonance frequency. Therefore, an oscillation signal having a frequency controlled by the applied control voltage is output from the base of Q2 to the outside via the capacitor C4.
[0017]
Next, FIG. 3 shows the configuration of the oscillator according to the second embodiment. Unlike the oscillation circuit shown in FIG. 1, in this example, an oscillation output signal is extracted from the emitter of the first transistor Q1 via the capacitor C4. Even in such a circuit configuration, a predetermined base bias current can be supplied to the first transistor Q1 in a similar manner while reducing the overall power consumption, and a stable oscillation signal can be extracted with excellent C / N characteristics. .
[0018]
Next, a configuration example of a communication apparatus according to the third embodiment is shown in FIG. 4 as a block diagram. In FIG. 4, VCO is a voltage controlled oscillator. The PLL-IC is a PLL control circuit, which receives the output signal of the VCO, compares the phase with the oscillation signal of the temperature compensation crystal oscillation circuit TCXO, and outputs a control signal so as to have a predetermined frequency and phase. The VCO receives a control voltage at the control terminal via the low-pass filter LPF, and oscillates at a frequency corresponding to the control voltage. This oscillation output signal is applied to mixer circuits MIXa and MIXb as local oscillation signals. The mixer circuit MIXa mixes the intermediate frequency signal output from the transmission circuit Tx and the local oscillation signal, and converts the frequency into a transmission frequency signal. This signal is amplified in power by the amplifier circuit AMPa and radiated from the antenna ANT via the duplexer DPX. A received signal from the antenna ANT is amplified by the amplifier circuit AMPb via the duplexer DPX. The mixer circuit MIXb mixes the output signal of the amplifier circuit AMPb and the local oscillation signal and converts them to an intermediate frequency signal. The reception circuit Rx obtains a reception signal by processing the signal.
[0019]
As the VCO in the communication apparatus, the oscillator shown in the first and second embodiments is used.
In this way, a communication device with low power consumption is configured as a whole by using a VCO with low power consumption.
[0020]
【The invention's effect】
According to the present invention, since the base bias current of the first transistor for oscillation is supplied from the second transistor, the series resistance value of the resistor bias circuit for supplying the base bias to the second transistor can be set high. As a result, power consumption can be reduced.
[0021]
Further, the present invention provides at least a resistor connected between the base of the first transistor and the ground, and connects the emitter of the first transistor to the base of the second transistor via a capacitor. The second transistor can be operated under a high current amplification factor due to the Darlington connection, and the input impedance of the amplifier circuit by the first and second transistors becomes higher, thereby increasing the stability of the oscillation operation.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an oscillator according to a first embodiment. FIG. 2 is a circuit diagram of a resonance circuit portion in the oscillator. FIG. 3 is a circuit diagram of an oscillator according to a second embodiment. FIG. 5 is a block diagram showing a configuration of a communication apparatus according to an embodiment. FIG. 5 is a circuit diagram showing a configuration of a conventional oscillator.
Q1-first transistor (oscillation transistor)
Q2-second transistor (R1, R2) -resistance voltage dividing circuit

Claims (2)

A resonance circuit is connected to the first transistor for oscillation, a resistance voltage dividing circuit is connected between the power source and the ground, an output of the resistance voltage dividing circuit is connected to a base of the second transistor, and a second The emitter of the transistor is connected to the base of the first transistor, the collectors of the first and second transistors are connected to the power supply, and the emitter current of the second transistor is supplied as the base bias current of the first transistor. And an oscillator in which at least a resistor is connected between the emitter of the first transistor and the ground, and the emitter of the first transistor is connected to the base of the second transistor via a capacitor . A communication apparatus provided with the oscillator according to claim 1 .

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