JP2602313B2 - Oscillation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit, and more particularly to a resonance of a ceramic resonator as a voltage controlled oscillator (VCO) of a phase locked loop (PLL) in an integrated circuit for FM stereo demodulation. The present invention relates to a one-terminal type oscillation circuit using a resonator.

[Conventional technology]

FIG. 2 shows a circuit diagram of a conventional one-terminal oscillator circuit.
In FIG. 2, a one-terminal type oscillation circuit main body 30 using a ceramic resonator X is used.

Here, a bias circuit 31 for applying an operation bias to the oscillation circuit main body 30 includes transistors 32 to 39. The reactance circuit 40 is a circuit for finely adjusting the oscillation frequency of the oscillation circuit main body 30.

The oscillation circuit body 30 oscillates at the parallel resonance frequency of the resonator X, for example, 456 kHz, and comprises npn transistors 41 and 42 forming a differential pair and an npn transistor 43 for a constant current source.
And pnp transistors 44 and 45 forming a current mirror type load
And two diodes 46 and 47 and one feedback capacitor 4
Consists of eight. Here, the ceramic resonator X does not have a bypass effect like the LC parallel element of the LC oscillation circuit, and the positive feedback required for oscillation is performed by the feedback capacitor 48.

[Problems to be solved by the invention]

In order to maintain a stable oscillating operation in the oscillation circuit body 30 using the ceramic oscillator X in FIG. 2, it is necessary that the amplification transistors 41 and 42 of the oscillation circuit body 30 are not actively operating in the oscillation stopped state. No. To realize this, the following two items can be considered.

Without applying DC negative feedback to the amplification transistors 41 and 42, the respective bias circuits for the transistors 41 and 42 are configured completely symmetrically.

A DC negative feedback circuit is provided to maintain the active operation of the amplification transistors 41 and 42.

Although the above configuration is employed in the bias circuit 31 of FIG. 2, it is difficult to obtain a stable operating condition due to manufacturing variations of each element in the integrated circuit. That is,
In FIG. 2, the respective currents of the bias current supply transistors 36 and 37 in the bias circuit 31 are equal, and the amplification / constant current transistor 4 in the oscillation circuit 30 is used.
Although 1,42,43 of h _PE that are identical is a condition for sustaining a stable oscillation, there are manufacturing variations, it is difficult to maintain the condition, leads to a decrease in yield.

[Means for solving the problem]

According to the configuration of the present invention, the differential amplifier circuit in which the emitters of the first and second transistors of one conductivity type are commonly connected to each other and the first constant current source is connected thereto, and the differential amplifier circuit is connected to the collector of the second transistor An output terminal, a resonator and a reactance circuit connected to the output terminal, a negative feedback circuit for performing negative feedback from the output terminal to the second transistor, and a high impedance circuit connected to a base of the first transistor. An oscillator configured to provide positive feedback from the output terminal to the first transistor via a first capacitor, wherein the bias circuit has a predetermined power supply different from an operation power supply of the circuit. Is a bias voltage source, and a positive feedback is applied from the output terminal to the base of the first transistor via the bias circuit via the first capacitor. And it said that there was Unishi.

Further, in the present invention, a third transistor of the opposite conductivity type, a fourth transistor of the one conductivity type, in which the emitter and the collector are respectively connected to one end of the power supply and the base is commonly connected, and the collector of the third transistor, A fifth transistor of the opposite conductivity type, a sixth transistor of the one conductivity type having an emitter and a collector connected to the emitter of the fourth transistor, respectively, and a base connected in common; a sixth transistor of the one conductivity type; A second constant current source connected between the power supply and the first terminal; a first resistor having one end connected to the emitter of the fifth transistor; and a collector connected to the power supply other than the power supply. The circuit connected to the other end is the bias circuit, the predetermined voltage source is connected between the other end of the first resistor and the other end of the power supply, and the first capacitor The base and emitter of said sixth transistor from service, via a second resistor can be configured to apply a positive feedback to the base of said first transistor,
In addition, the output terminal is connected to the base and the one conductivity type
A transistor, an eighth transistor of one conductivity type having a base and collector connected in common and connected to the emitter of the seventh transistor, and a base and collector connected in common and having an emitter connected to the emitter of the eighth transistor. A ninth transistor of the opposite conductivity type connected thereto, a third constant current source connected between the collector of the ninth transistor and the other end of the power supply, and a third constant current source connected to the collector of the ninth transistor. A second terminal connected to the other end of the power supply via a resistor;
A circuit comprising the capacitor and the negative feedback circuit,
A common connection point between the third resistor and the second capacitor may be connected to a base of the second transistor.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an oscillation circuit according to one embodiment of the present invention. In FIG. 1, in an oscillation circuit according to an embodiment of the present invention, the emitters of a first transistor 10 and a second transistor 11 having a first polarity are commonly connected to a first constant current source 13, Transistor 10
The collector and base of the third transistor 8 of the second polarity having the opposite polarity to the first transistor 10 and the base of the fourth transistor 9 of the second polarity are connected to the collector of the third transistor 8 and the fourth transistor 9. The emitter of the transistor 9 is connected to the first power supply, the collector of the fourth transistor 9 is connected to the collector of the second transistor 11, and the collector of the second transistor 11 is connected to the fifth transistor 21 of the first polarity. The collector of the fifth transistor 21 is connected to the first power supply, the collector of the sixth transistor 22 of the first polarity and the base are connected to the emitter of the fifth transistor 21, The emitter of the sixth transistor 22 is connected to the emitter of the seventh transistor 23 of the second polarity, and the base and the collector of the seventh transistor 23 are shared by the second constant current. It is connected to the 26. The base and the collector of the seventh transistor 23 are further connected to the base of the second transistor 11 via a first resistor 24, and the base of the second transistor 11 is further connected via a first capacitor 25. Connected to a second power supply and connected to an eighth
The emitter of the transistor 14 is connected to the first power supply,
The base of the eighth transistor 14 is connected to the base of the ninth transistor 15 of the first polarity, and the ninth transistor 15
Is connected to the first power supply, the collector of the eighth transistor 14 is connected to the third power supply 6 through the second resistor 5, and the collector of the eighth transistor 14 is connected to the second power supply of the second polarity. Connected to the emitter of 10 transistors 16
The collector of the tenth transistor 16 is connected to the second power supply, and the base of the tenth transistor 16 is connected to the eleventh of the first polarity.
The base of the tenth transistor 16 is connected to the collector of the second transistor 11 via the second capacitor 12, and the collector of the eleventh transistor 17 is connected to the ninth transistor. The emitter of the eleventh transistor 17 is connected to the third constant current source 18, and the emitter of the eleventh transistor 17 is connected to the base of the first transistor 10 via the third resistor 19. , The collector of the second transistor 11 is used as the output terminal 7, the resonator X is connected between the output terminal 7 and the second power supply, and the output terminal is connected to the reactance circuit 4.

That is, the oscillation circuit of the present embodiment includes the oscillation circuit main body 1, the high impedance bias circuit 2, and the DC negative feedback circuit 3, and is configured.

Here, a differential amplifier including a pair of npn transistors 10 and 11, a constant current source 13, and pnp transistors 8 and 9 serving as a current mirror load circuit is configured and positively fed back by a capacitor 12.
npn transistors 21, 22, pnp transistor 23, constant current source 26,
The DC negative feedback circuit 3 including the resistor 24 and the capacitor 25 provides DC negative feedback. Further, npn transistors 14, 16, npn transistors 15, 17, and constant current source 1
8, a positive impedance is fed back to the transistor 10 via the capacitor 12 by the high impedance bias circuit 2 including the resistors 5, 19 and the constant voltage source 6. Further, the base of the transistor 11 is Negative feedback to the terminal is performed through the emitter follower of the DC negative feedback circuit 3.

The oscillation output of this circuit is positively fed back to the base of the transistor 10 via the capacitor 12, the base of the transistor 17, and the resistor 19, but for stable positive feedback, make sure that the feedback signal from the capacitor 12 is not affected. , The base of the transistor 10 is connected to the high impedance circuit 2 which is not influenced by the feedback signal in terms of current.

If the necessary base current for the transistor 10 is always supplied as much as necessary, the circuit is not affected by the feedback by the capacitor 12, so the circuit consisting of the transistors 14 to 17 always supplies the current required for the base current of the transistor 10. doing. Transistors 15 and 17 and transistors 14 and 16 each use the same type of transistor.
Since the collector currents of the transistors 15 and 17 are always the same, the base currents of the transistors 15 and 17 are always the same, and the collector currents and the base currents of the transistors 14 and 16 are also always the same.

If there is any change in the base current of the transistor 10, the base current of the transistor 17 also changes.However, even if there is any change in the base current of the transistor 17, the base of the transistor 16 is connected to the base of the transistor 17. , The base current of transistor 16 operates to supply it. Therefore, it is possible to always supply the base current of the transistor 10 as much as necessary, and the positive feedback signal from the capacitor 12 is not affected.

As a result, the output impedance of the collector terminal of the transistor 11 is kept high, and the Q of the ceramic resonator X connected here does not decrease. Further, since the bypass capacitor 25 is provided at the base of the transistor 11, the AC component (oscillation frequency component) is almost bypassed, and only the DC component is negatively fed back.

When the current flowing through the reactance circuit 4 is zero, the transistors 10 and 11 of the differential pair operate stably in a balanced state (here, the constant current 18 and the constant current 26 are assumed to be equal). 11 base current is equal to, V _bE of the base-emitter voltage V _bE and transistor 21 of the transistor 17 is equal, transistor 16, transistor
23 V _BEs are equal. For this reason, the output terminal 7 of the oscillation circuit main body 1 is fixed at a stable potential higher than the DC voltage source 6 by the V _{BE of the} transistor 22, and the reference potential of the output terminal 7 is determined by the potential of the DC voltage source 6. Can be easily set.

If the reactance circuit 4 has an offset current, the output DC voltage at the collector terminal of the transistor 11 decreases due to the offset current, for example, and the DC negative feedback circuit 3
As a result, the base potential of the transistor 11 which is fed back decreases, the collector current of the transistor 10 increases, and the currents of the transistors 8 and 9 which are current mirror load circuits increase. As a result, the difference between the collector currents of the transistors 10 and 11 of the differential pair becomes stable in a state where the difference is equal to the offset current.

In other words, as long as the offset current does not become larger than the current of the constant current source 13, the transistors 10 and 11 of the differential pair
It operates actively and can maintain stable oscillation.

〔The invention's effect〕

As described above, according to the present invention, by providing a DC negative feedback circuit, a stable DC operation voltage can be obtained even with variations in circuit elements, so that a stable oscillation operation can be performed and the oscillation frequency is bypassed. Since it has a method and a high impedance bias circuit, there is an effect that more stable oscillation operation can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a one-terminal oscillation circuit according to one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional one-terminal oscillation circuit. 1. Oscillation circuit main body, 2 .... High impedance bias circuit, 3 .... DC negative feedback circuit, 4, 40 ... Reactance circuit, 5, 19, 24, 49 ... Resistance, 6 ... DC voltage source, 7 , 50 ……
Output terminal, 8, 9, 10, 11, 14, 15, 16, 17, 21, 22, 23, 32 to 39, 41
~ 45 ... Transistor, 12,48 ... Return capacitance, 13,18,26
... constant current source, 25 ... bypass capacitance, 46, 47 ... diodes.

Claims (3)

(57) [Claims] 1. A differential amplifier circuit in which emitters of first and second transistors of one conductivity type are commonly connected and a first constant current source is connected, and an output connected to a collector of the second transistor. A terminal, a resonator and a reactance circuit connected to the output terminal, a negative feedback circuit for performing negative feedback from the output terminal to the second transistor, and a high impedance bias connected to a base of the first transistor. And an oscillator configured to provide a positive feedback from the output terminal to the first transistor via a first capacitor, wherein the bias circuit has a predetermined power supply different from an operation power supply of the circuit. A voltage source is a bias voltage source, and a positive feedback is applied from the output terminal to the base of the first transistor through the bias circuit via the first capacitor. Oscillating circuit, characterized in that the. And a third transistor of the opposite conductivity type, a fourth transistor of the one conductivity type, wherein the emitter and the collector are respectively connected to one end of the power supply and the base is connected in common, a collector of the third transistor, and a collector of the third transistor. A fifth transistor of opposite conductivity type, a sixth transistor of one conductivity type having an emitter and a collector respectively connected to the emitter of the fourth transistor, and a base commonly connected, an emitter of the sixth transistor and the other end of the power supply And a first resistor having one end connected to the emitter of the fifth transistor, and a collector connected to the other end of the power supply. Is connected to the predetermined voltage source between the other end of the first resistor and the other end of the power supply. Sixth transistor base and emitter of the oscillation circuit of the second through said resistor of the first transistor base to a positive feedback of the applied manner the Claims first claim of. 3. A one-conductivity-type seventh transistor having the output terminal connected to a base, and a one-conductivity-type eighth transistor having a base and collector connected together and connected to the emitter of the seventh transistor. A ninth transistor of the opposite conductivity type having a base and a collector commonly connected and an emitter connected to the emitter of the eighth transistor, and connected between the collector of the ninth transistor and the other end of the power supply. A circuit comprising a third constant current source and a second capacitor connected to the other end of the power supply via a third resistor at the collector of the ninth transistor is referred to as the negative feedback circuit. 2. The oscillation circuit according to claim 1, wherein a common connection point of the resistor and the second capacitor is connected to a base of the second transistor.