JP6560077B2 - Oscillator circuit - Google Patents

Description

  The present invention relates to an oscillation circuit using an electromechanical vibrator.

  Oscillation circuits using crystal vibrators or the like that are electromechanical vibrators are often used in electronic circuits. FIG. 4 shows a conventional oscillation circuit using a crystal resonator (FIG. 2 of Patent Document 1). This oscillation circuit is a Colpitts type, the crystal resonator X11 is connected to the base terminal (node N11) of the oscillation transistor Q11, the capacitor C11 is connected between the base terminal and the emitter terminal (node N12), the emitter terminal and the ground A capacitor C12 is connected between them.

  The oscillation voltage V12 appearing at the load resistor R11 connected to the emitter terminal of the oscillation transistor Q11 becomes the output oscillation voltage Vout via the capacitor C15. The oscillation voltage V12 is rectified by diodes D1 and D2 capacitively coupled by the capacitor C13, and becomes a rectified voltage V13 smoothed by the capacitor C14 at the node N13.

  The obtained rectified voltage V13 is converted into a current by being input to the base terminal of the transistor Q12, and negatively fed back to the base terminal of the oscillation transistor Q11 via the resistor R12 connected to the collector terminal of the transistor Q12. R13 is a base bias resistor of the oscillation transistor Q11, R14 is a rectifying bias resistor, and D3 is a rectifying bias diode.

  In an oscillation circuit using a crystal resonator, when the power supply voltage Vcc is low, it may be desired to increase the amplitude of the oscillation voltage V12 obtained as much as possible and to suppress the distortion of the waveform of the oscillation voltage V12.

  Therefore, in the conventional oscillation circuit shown in FIG. 4, in order to maintain the amplitude level of the output oscillation voltage Vout at a predetermined value, the base of the oscillation transistor Q11 corresponds to the amplitude of the oscillation voltage V12 output to the emitter terminal of the oscillation transistor Q11. Negative feedback control is performed on the bias voltage V11. As a result, it is possible to increase the amplitude of the oscillation voltage V12 while reducing distortion of the waveform of the oscillation voltage V12 output from the emitter terminal of the oscillation transistor Q11.

  That is, when the amplitude of the oscillation voltage V12 is large, the base bias voltage V11 of the oscillation transistor Q11 is lowered. That is, negative feedback control is performed so as to reduce the amplitude of the oscillation voltage V12 by reducing the variable impedance between the collector terminal and the emitter terminal of the transistor Q12 connected in parallel to the resonance circuit.

  Conversely, when the amplitude of the oscillation voltage V12 is small, the base bias voltage V11 of the oscillation transistor Q11 is increased. That is, negative feedback control is performed so as to increase the drive capability of the oscillation transistor Q11 and increase the amplitude of the oscillation voltage V12 by increasing the variable impedance between the collector terminal and the emitter terminal of the transistor Q12 connected in parallel to the resonance circuit. .

JP 59-010617 A

  However, when the amplitude of the oscillation voltage V12 is increased by increasing the base bias voltage V11 of the oscillation transistor Q11 and increasing the amplification capability of the oscillation transistor Q11 in the conventional oscillation circuit of FIG. Since the collector is connected to the power supply terminal of the voltage Vcc, a situation occurs in which the base bias ass voltage V11 exceeds the collector voltage (power supply voltage Vcc).

  Therefore, on the positive side of the oscillation voltage V12, the base-collector junction voltage of the oscillation transistor Q11 becomes the forward bias voltage. When the base bias voltage V11 of the oscillation transistor Q11 is further increased, the forward bias voltage between the base and the collector is further increased, so that the waveform of the oscillation voltage V12 is clamped as shown in FIG.

  When the waveform of the oscillation voltage V12 is clamped, the amplitude decreases from Vp1 to Vp2, as shown in FIG. As a result, as shown in FIG. 6, the rectified voltage V13 used for the negative feedback control decreases, so that the negative feedback control is performed in the direction of increasing the base bias voltage V11 of the oscillation transistor Q11. Accordingly, the waveform of the oscillation voltage V12 is more strongly clamped, and the rectified voltage V13 is further reduced. The change in the base bias voltage V11 and the rectified voltage V13 before and after the clamp is generated. The direction is reversed.

  For this reason, the base bias voltage V11 sticks to the upper limit voltage, and the waveform of the oscillation voltage V12 remains largely distorted. As described above, the conventional oscillation circuit of FIG. 4 may not be suitable for the purpose of increasing the amplitude of the oscillation voltage V12 and reducing the distortion.

  Further, in the conventional oscillation circuit of FIG. 4, since the resonance circuit and the rectification circuit are connected via the capacitor C14, the rectification circuit having a relatively low impedance has a deep influence on the resonance circuit and influences on the oscillation itself. Therefore, there is a problem that it is difficult to set constants for each element.

  It is an object of the present invention to provide an oscillation circuit that can improve these and reduce the distortion of the waveform of the oscillation voltage while increasing the amplitude of the oscillation voltage.

  In order to solve the above problem, an invention according to claim 1 is an oscillation circuit using an electromechanical vibrator as a part of a resonance circuit, an oscillation transistor having a base terminal connected to the resonance circuit, and A first buffer circuit having a high input impedance for inputting a signal; a rectifier circuit for rectifying an output signal of the first buffer circuit; an inverting amplifier for inverting and amplifying a rectified voltage obtained by the rectifier circuit; And a feedback circuit for negatively feeding back the output signal of the amplifier to the base terminal of the oscillation transistor.

According to a second aspect of the present invention, in the oscillation circuit according to the first aspect, the oscillation transistor has a bias voltage applied to the base terminal, a load resistor connected to the emitter terminal, and a power supply terminal connected to the collector terminal. was made bipolar transistor, said first buffer circuit, the base terminal of the oscillation transistor is connected to the base terminal, a power supply terminal connected to the collector terminal and to the rectified voltage from the emitter terminal is obtained bipolar It is characterized by comprising the following transistors .

  The invention according to claim 3 is the oscillation circuit according to claim 1 or 2, wherein the capacitor is connected between the electromechanical vibrator and the base terminal of the oscillation transistor, and the capacitor and the electromechanical vibration. And a second buffer circuit having a high input impedance connected to the common connection point with the child, the output oscillation voltage being extracted from the output side of the second buffer circuit.

Such invention in claim 4, in the oscillation circuit according to claim 2, replacing the bipolar transistor as transistor and the first buffer circuit of the bipolar as the oscillation transistor, the MOS transistors, respectively, the the base terminal to the gate terminal, the emitter terminal to a source terminal, the collector terminal to the drain terminal, is characterized in that each replaced.

  According to the present invention, the voltage at the base terminal of the oscillation transistor is rectified via the first buffer circuit having a high input impedance, the rectified voltage is inverted and amplified, and the voltage is negatively applied to the base terminal of the oscillation transistor via the feedback circuit. Since feedback is performed, the direction of change of the base bias voltage of the oscillation transistor is the same as the direction of change of the rectified voltage before and after the clamp state occurs, and the base bias voltage of the oscillation transistor is Sticking to the upper limit is prevented. Further, since the rectified voltage for generating the negative feedback signal is rectified after being input from the base terminal of the oscillation transistor to the first buffer circuit having a high input impedance, the resonance circuit and the rectifier circuit can be separated and rectified. The constant of the oscillation circuit can be set without being influenced by the constant of the circuit.

1 is a block diagram of an oscillation circuit according to a first exemplary embodiment of the present invention. 1 is a circuit diagram of an oscillation circuit according to a first embodiment of the present invention. It is a block diagram of the oscillation circuit of the 2nd Example of this invention. It is a circuit diagram of the conventional oscillation circuit. FIG. 5 is an operation waveform diagram of the oscillation circuit of FIG. 4. FIG. 5 is an operation characteristic diagram of the oscillation circuit of FIG. 4. FIG. 3 is an operational characteristic diagram of the first embodiment of the present invention.

<First embodiment>
FIG. 1 shows a block diagram of an oscillation circuit according to a first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a resonance circuit composed of a crystal resonator X1 and capacitors C1 and C2. Reference numeral 30 denotes a first buffer circuit having a high input impedance whose input side is connected to the node N1, 40 denotes a rectifier circuit that rectifies the output voltage of the first buffer circuit 30, and 50 inverts and amplifies the output signal of the rectifier circuit 40. An inverting amplifier 50 is a feedback circuit that negatively feeds back the output voltage of the inverting amplifier 40 to the node N1 and sets the base bias voltage at the node N1.

  The oscillation signal generated by the resonance circuit 10 and the oscillation amplifier 20 is impedance-converted by the first buffer circuit 30, rectified by the rectifier circuit 40, then inverted and amplified by the inverting amplifier 50, passed through the feedback circuit 60, Negative feedback to N1. In this embodiment, a portion (first buffer circuit 30, rectifier circuit 40, inverting amplifier 50, feedback circuit 60) that generates a negative feedback signal from an oscillation voltage is used as a portion (oscillation amplifier 20) that generates an output oscillation voltage Vout. ), The distortion of the waveform of the output oscillation voltage Vout can be reduced while maintaining the amplitude of the output oscillation voltage Vout at a predetermined magnitude. At this time, the circuit related to negative feedback is also separated from the resonance circuit 10 by the first buffer circuit 30 having a high input impedance, and therefore the circuit related to negative feedback does not adversely affect the oscillation operation.

  FIG. 2 shows a specific circuit of the oscillation circuit of FIG. The oscillation amplifier 20 includes an NPN oscillation transistor Q1 and a load resistor R1 connected to the emitter terminal thereof. The output oscillation voltage Vout is taken out from the emitter terminal of the oscillation transistor Q1 via the DC cut capacitor C4. The first buffer circuit 30 and the rectifier circuit 40 are composed of the same NPN type and high input impedance buffer transistor Q2 as the oscillation transistor Q1, a resistor R2, and a capacitor C3. The inverting amplifier 50 includes an operational amplifier 51 to which a reference voltage Vref is applied to a non-inverting input terminal, and resistors R3 and R4 that determine a gain.

  The node N3 of the emitter terminal of the buffer transistor Q2 has a rectified voltage obtained by subtracting the base-emitter junction voltage of the buffer transistor Q2 from the voltage of the node N1 in which the oscillation voltage of the AC component is superimposed on the base bias voltage V1 of the oscillation transistor Q1. V3 is output. Therefore, even if the amplitude of the oscillation voltage V2 at the node N2 increases, the base-collector junction voltage of the transistor Q1 becomes a forward voltage, and the waveform of the oscillation voltage V2 is clamped, the buffer transistor Q2 The rectified voltage V3 at the emitter terminal of the current does not drop below the voltage when the waveform is not clamped.

  Further, when the waveform of the oscillation voltage V2 at the emitter terminal of the oscillation transistor Q1 is clamped, the current flowing through the base-collector junction of the oscillation transistor Q1 increases, so that the base-collector voltage slightly increases. Thus, the oscillation voltage V2 at the emitter terminal slightly increases. Thus, even if the waveform of the oscillation voltage V2 at the node N2 is clamped, the rectified voltage V3 at the node N3 rises with a slight gradient as shown in FIG.

  Therefore, the direction of change of the base bias voltage V1 at the node N1 is maintained in the same direction as the change of the rectified voltage V3 at the node N3 before and after the clamp state occurs. The base bias voltage V1 of the oscillation transistor Q1 can be avoided from sticking to the upper limit.

  Further, the rectified voltage V3 at the node N3 is input from the base terminal of the oscillation transistor Q1 to the base terminal of the buffer transistor Q2 having a high input impedance, and is rectified, whereby the resonance circuit 10 and the rectifier circuit 40 are connected. Since the interval is separated, the constant of the oscillation circuit can be set without being affected by the constant of the rectifier circuit 40.

<Second embodiment>
FIG. 3 is a diagram showing an oscillation circuit according to a second embodiment of the present invention. Here, the resonant circuit 10A is configured by connecting a DC cut capacitor C5 between the node N4 of the crystal unit X1 and the node N1 of the base terminal of the oscillation transistor Q1. The oscillation voltage V4 appearing at the node N4 is taken out as the output oscillation voltage Vout via the second buffer circuit 70 having a high input impedance.

  As described above, in this embodiment, the oscillation voltage V4 is extracted from the node N4 different from the node N1 in FIG. 2 that extracts the oscillation voltage for rectification through the buffer transistor Q2 having a high input impedance. Yes. For this reason, it is possible to reduce the influence of the distortion of the waveform of the oscillation voltage V4 by the oscillation transistor Q1 and to extract a signal, and to further reduce the influence of the extraction of the oscillation voltage V4 on the oscillation transistor Q1 side. Can do.

10, 10A: Resonant circuit 20: Oscillation amplifier, Q1: Oscillation transistor 30: First buffer circuit with high input impedance, Q2: Buffer transistor 40: Rectifier circuit 50: Inverting amplifier 60: Feedback circuit 70: High input impedance Second buffer circuit

Claims (4)

In an oscillation circuit using an electromechanical vibrator as a part of a resonance circuit,
An oscillation transistor having a base terminal connected to the resonance circuit; a first buffer circuit having a high input impedance for inputting a signal of the base terminal; a rectifier circuit for rectifying an output signal of the first buffer circuit; An oscillation circuit comprising: an inverting amplifier that inverts and amplifies a rectified voltage obtained by the rectifier circuit; and a feedback circuit that negatively feeds back an output signal of the inverting amplifier to the base terminal of the oscillation transistor. The oscillation circuit according to claim 1,
The oscillation transistor is a bipolar transistor in which a bias voltage is applied to the base terminal, a load resistor is connected to the emitter terminal, and a power supply terminal is connected to the collector terminal .
The first buffer circuit includes a bipolar transistor having a base terminal connected to a base terminal of the oscillation transistor, a collector terminal connected to a power supply terminal, and the rectified voltage obtained from an emitter terminal. An oscillation circuit.
The oscillation circuit according to claim 1 or 2,
A capacitor connected between the electromechanical vibrator and the base terminal of the oscillation transistor, and a second buffer having a high input impedance, the input side of which is connected to a common connection point between the capacitor and the electromechanical vibrator And an oscillation circuit, wherein an oscillation voltage is extracted from an output side of the second buffer circuit. The oscillation circuit according to claim 2 ,
Said bipolar transistor as a transistor and the first buffer circuit of the bipolar as the oscillation transistor, respectively replaced with the MOS transistor, the base terminal to the gate terminal, the emitter terminal to a source terminal, the collector terminal An oscillation circuit characterized by replacing each with a drain terminal .

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