JP2008004977A - Oscillating circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillating circuit in which an oscillator is provided, with early oscillation start time, and the non-deformed waveform of signal. <P>SOLUTION: The oscillating circuit has a resonator, such as an SAW resonator; a differential amplifier for amplifying signal, such as a high-frequency signal generated in the resonator, and outputting a feedback signal to the resonator; and a means for changing a gain of the differential amplifier in a predetermined time, from power-on and in a time point after elapse of the predetermined time. As a means for changing a gain, a gain adjusting circuit is provided on the differential amplifier, with a first transistor 13 connected to a constant voltage source and a second transistor 14 connected, by changing a switch 15 to the constant voltage source or a second power source. Since connection/disconnection of the switch 15 can shorten the time required for starting the oscillation with stable amplitude, and the gain of the circuit can be suppressed after stable oscillation, the oscillating circuit can be realized in which the waveform of the signal is not deformed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oscillation circuit including a differential amplifier, and more particularly to an oscillation circuit in which an oscillation start time is early and a signal waveform is not crushed.

  Conventionally, in an oscillation circuit using a SAW (Surface Acoustic Wave) resonator, a plurality of differential amplifiers are arranged to make the gain of the oscillation circuit larger than the insertion loss of the SAW resonator, thereby forming a feedback loop. .

Reference 1 describes an oscillator using a SAW resonator. This document discloses a voltage controlled oscillator having a small frequency variable range by correcting temperature characteristics, a clock converter including the voltage controlled oscillator, and an electronic device using the clock converter. That is, a tank circuit composed of an LC resonance circuit is provided at the output part of the SAW resonator constituting the voltage-controlled SAW oscillator, and the change in phase of the resonance signal of the SAW resonator is canceled using the temperature characteristic of the tank circuit element. Thus, the frequency deviation-temperature characteristic of the SAW resonator is corrected. This makes it possible to obtain frequency deviation-temperature characteristics substantially the same as those of a conventional AT crystal resonator without increasing the circuit scale of the voltage-controlled SAW oscillator. Further, it is possible to generate a clock signal with less jitter than the AT crystal unit. Furthermore, even if the power supply voltage is lowered, the frequency variable range can be easily compensated and the frequency deviation of the clock signal can be maintained with high accuracy.
JP 2004-120353 A

In such an oscillation circuit, if the gain of the oscillation circuit is too large, the amplitude of the signal swings beyond the power supply voltage and the waveform of the signal is crushed. Therefore, it is necessary to suppress the gain of the oscillation circuit to some extent. On the other hand, from when the power is turned on until the amplitude of the oscillation signal is stabilized, it takes time until stable oscillation occurs unless the gain of the oscillation circuit is sufficient.
The present invention has been made under such circumstances, and provides an oscillation circuit that has an early oscillation start time and at the same time the signal waveform does not collapse.

  One aspect of the oscillation circuit of the present invention includes a resonator and a differential amplifier that amplifies and outputs a signal generated by the resonator and outputs a feedback signal to the resonator. It is characterized by having means for changing the gain of the differential amplifier between a predetermined time and after the predetermined time has elapsed. The differential amplifier may be configured such that the gain after the predetermined time has elapsed is smaller than the gain at the predetermined time from when the power is turned on. The differential amplifier includes a pair of load resistors whose one ends are connected to a first power supply, a pair of differential transistors connected to the other ends of the pair of load resistors, and currents of the pair of differential transistors You may make it have the gain adjustment circuit which changes the gain of the said differential amplifier between the common connection part of an outflow end, and a 2nd power supply. The gain adjustment circuit includes a first transistor and a second transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power source, and the first transistor A constant voltage source connected to the control terminal; and a switch connected to the control terminal of the second transistor and conducting the second transistor to the constant voltage source or the second power source. The control terminal of the second transistor is made conductive to the constant voltage source for a predetermined time from the time point, and the control terminal of the second transistor is made conductive to the second power source after the predetermined time has elapsed. May be switched. The gain adjustment circuit controls a first transistor and a second transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power source, and controls the first transistor. A first constant voltage source connected to an end; a second constant voltage source for supplying a voltage to the second transistor; and the second constant voltage source between the second transistor and the second constant voltage source. And a CR circuit for limiting the voltage supplied to the two transistors. The gain adjustment circuit includes: a transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power supply; and a first constant voltage that supplies a first voltage to the transistor. A source, a second constant voltage source for supplying a second voltage to the transistor, and between the first constant voltage source and the transistor and between the second constant voltage source and the transistor. A CR circuit that controls the voltage supplied to the transistor within the range from the first voltage to the second voltage may be provided. The differential amplifier includes the pair of differential transistors, and a plurality of load resistors connected in parallel between current inflow ends of the first power source and the pair of differential transistors, and the load resistors The gain of the differential amplifier may be changed by controlling the load resistance value between the first power supply and the pair of differential transistors by turning on and off the switches connected in series. The differential amplifier includes the pair of differential transistors and a plurality of load resistors connected in series between current inflow ends of the first power source and the pair of differential transistors, respectively. The gain of the differential amplifier is changed by controlling the load resistance value between the first power supply and the pair of differential transistors by turning on and off a switch connected in parallel with the load resistance between both terminals of You may do it. The differential amplifier may include an inductor instead of the load resistor.

  The time required to start oscillation with a stable amplitude can be shortened, and after stable oscillation, by suppressing the gain of the circuit, it is possible to realize an oscillation circuit that does not collapse the signal waveform.

According to the present invention, in an oscillation circuit having a resonator such as a SAW resonator, the gain of the circuit is increased until the amplitude of the oscillation signal is stabilized after the power is turned on, and the gain of the circuit is suppressed after the stable oscillation. The configuration is characterized in that the oscillation start time is early and the waveform of the signal is not crushed at the same time.
Hereinafter, embodiments of the invention will be described with reference to examples.

First, Embodiment 1 will be described with reference to FIGS. 1 to 3 and FIG.
1 is a circuit diagram of an oscillation circuit having a resonator using, for example, a SAW resonator, FIG. 2 is a circuit diagram of a differential amplifier used in the oscillation circuit of FIG. 1, and FIG. 3 is a difference of FIG. FIG. 8 is a circuit diagram of the switch 15 used in the dynamic amplifier, and FIG. 8 shows the oscillation amplitude when the feedback circuit is configured by the differential amplifier of FIG.
As shown in FIG. 1, an oscillation circuit including a SAW resonator used in this embodiment includes a SAW resonator 1 having a predetermined resonance frequency, a plurality of differential amplifiers 2, 3, 4, 5 and these. Capacitors 6, 7, and 8 inserted on the input side and output side of the differential amplifier, and a pair of output transistors 10a and 10b. A positive feedback loop 11 is formed by the oscillation differential amplifiers 2 and 3, the feedback differential amplifier 4 and the SAW resonator 1.

  A high-frequency signal having a predetermined resonance frequency resonated by the SAW resonator 1 is input to the non-inverting input terminal (+) of the oscillation differential amplifier 2 via the capacitor 6, and the first output terminal of the differential amplifier 2. Is output from. This output signal is input to at least one other differential amplifier such as the differential amplifier 3, and then input to the non-inverting input terminal (+) of the differential amplifier 5 for output. Is output from the output terminal. The signal output from the first output terminal of the output differential amplifier 5 is input to the output transistor 10a and output (OUTN) from the output transistor 10a.

  In order to start oscillation in the oscillation circuit, the sum of the gains of the differential amplifiers constituting the feedback loop 11 needs to be larger than the insertion loss of the SAW resonator 1. However, if the gain becomes too large, the amplitude of the signal fluctuates beyond the power supply voltage, causing a problem that the signal waveform is crushed when amplified by the differential amplifier. For this reason, it is necessary to suppress the gain of the differential amplifier to some extent, but if the gain is suppressed, the amplification factor of the differential amplifier becomes small, so it takes time to oscillate with a stable amplitude. Occurs. This embodiment solves these problems by using the differential amplifier shown in FIG.

  The differential amplifier shown in FIG. 2 includes a pair of differential transistors 16a and 16b. As these differential transistors, for example, n-type MOS transistors are used. The differential transistors 16a and 16b have drains connected to a power source (VDD) via load resistors 17a and 17b, and sources connected to two constant current sources including the transistors 13 and 14, respectively. The source sides of the transistors 13 and 14 are grounded (GND).

  As described above, the differential amplifier includes two constant current sources including the transistor 13 and constant current source including the transistor 14. Both transistors 13 and 14 of the constant current source are connected to a constant voltage source (VG) that applies a voltage to the gate, and a switch 15 is interposed between the gate of the transistor 14 and the constant voltage source (VG). The switch 15 is configured so that the gate and the constant voltage source (VG) are intermittently connected.

  When the power is turned on, the switch 15 is switched to the constant voltage side to apply a voltage from the constant voltage source (VG) to the gate of the transistor 14. Then, the current flowing through the differential amplifier is increased to increase the gain. By increasing the gain of the differential amplifier when the power is turned on, the minute signal amplitude of the SAW resonator 1 in FIG. 1 can be increased in a short time. When the switch 15 is switched to the ground (GND) side after a predetermined time has elapsed after the power is turned on, the differential amplifier has only one constant current source including the transistor 13, and as a result, the current flowing through the differential amplifier is small. The gain is suppressed. By using the differential amplifier shown in FIG. 2, it is possible to shorten the time until oscillation starts with a stable amplitude, and to realize an oscillation circuit that does not collapse the signal waveform by suppressing the gain of the circuit after stable oscillation It is.

  The oscillation amplitude when the feedback circuit is configured by the differential amplifier shown in FIG. 2 is as shown in FIG. In the prior art, it took about 14 μs from turning on the power to oscillate with a stable amplitude (see FIG. 11). However, if the switch 15 is switched to the ground (GND) side after 3.5 μs using this differential amplifier, the power Oscillation starts with a stable amplitude after about 5 μs.

FIG. 3 is an example of the switch 15 shown in FIG.
The transistor 28 is connected between the gate of the transistor 14 and the constant voltage source (VG), the drain of the transistor 28 and the constant voltage source (VG) are connected, and the source and the gate of the transistor 14 are connected. Further, a transistor 29 having a drain connected between the source of the transistor 28 and the gate of the transistor 14 and the source grounded is disposed. A switch (VSW) for applying a VDD or VSS (GND) voltage is connected to the gates of the transistors 28 and 29 via a resistor 31. An inverter 30 is connected between the resistor 31 and the gate of the transistor 29.

  When the VDD voltage is applied to the switch (VSW) when the power is turned on, the transistor 28 is turned on and the transistor 29 is turned off. As a result, the transistor 14 as an additional current source is turned on. After that, when a VSS voltage (GND) is applied to the switch (VSW) after a predetermined time has elapsed after the power is turned on, the transistor 29 is turned on, the transistor 28 is turned off, and the transistor 14 is turned off.

Next, Embodiment 2 will be described with reference to FIG.
FIG. 4 is a circuit diagram of a differential amplifier used in the oscillation circuit of FIG.
The differential amplifier shown in FIG. 4 includes a pair of differential transistors 21a and 21b. As these differential transistors, for example, n-type MOS transistors are used. The differential transistors 21 a and 21 b have drains connected to a power source (VDD) via load resistors 19 a, 19 b, 20 a and 20 b, and sources connected to a constant current source including the transistor 22. The source side of the transistor 22 is grounded (GND). The load resistors 20a and 20b are connected in parallel to the load resistors 19a and 19b, respectively, and include switches 18a and 18b, respectively, so that the load resistors 20a and 20b are connected to and separated from the amplifier circuit. A constant voltage source (VG) for applying a gate voltage is connected to the gate of the transistor 22 serving as a constant current source.

  The differential amplifier increases the gain by turning off the switches 18a and 18b when the power is turned on, so that the load resistances are only the load resistances 19a and 19b. Thereafter, after a predetermined time has elapsed after the power is turned on, the switches 18a and 18b are turned on to reduce the gain by making the load resistances parallel combined resistances of the load resistances 19a and 19b and the load resistances 20a and 20b. By using such a differential amplifier, it is possible to reduce the time required to start oscillation with a stable amplitude, and it is possible to realize an oscillation circuit that does not collapse the signal waveform by suppressing the circuit gain after stable oscillation. is there.

Next, Example 3 will be described with reference to FIG.
FIG. 5 is a circuit diagram of a differential amplifier used in the oscillation circuit of FIG.
The differential amplifier shown in FIG. 5 includes a pair of differential transistors 26a and 26b. As these differential transistors, for example, n-type MOS transistors are used. The differential transistors 26 a and 26 b have drains connected to a power source (VDD) via load resistors 23 a, 23 b, 24 a and 24 b, and sources connected to a constant current source including the transistor 27. The source side of the transistor 27 is grounded (GND). The load resistors 24a and 24b are connected in series to the load resistors 23a and 23b, respectively, the switches 25a and 25b are connected in parallel, and the load resistors 24a and 24b are connected to and separated from the amplifier circuit. A constant voltage source (VG) for applying a gate voltage is connected to the gate of the transistor 27 serving as a constant current source.

  The differential amplifier increases the gain by turning off the switches 25a and 25b when the power is turned on to make the load resistance a series combined resistance of the load resistances 23a and 24a and a series combined resistance of the load resistances 23b and 24b. Thereafter, the switches 25a and 25b are turned on after elapse of a predetermined time after the power is turned on, and the load resistance is set to the on-resistance of the switch 25a, the parallel combined resistance of the load resistance 24a and the series combined resistance of the load resistance 23a, and the on-resistance of the switch 25b. The gain is suppressed as a parallel combined resistance of the load resistance 24b and a series combined resistance of the load resistance 23b. By using such a differential amplifier, it is possible to reduce the time required to start oscillation with a stable amplitude, and it is possible to realize an oscillation circuit that does not collapse the signal waveform by suppressing the circuit gain after stable oscillation. is there.

Next, Embodiment 4 will be described with reference to FIGS.
FIG. 6 is a circuit diagram of a differential amplifier used in the oscillation circuit of FIG. 1, and FIG. 9 is an oscillation amplitude diagram when a feedback circuit is constituted by the differential amplifier of this embodiment.
The differential amplifier shown in FIG. 6 includes a pair of differential transistors 36a and 36b. As these differential transistors, for example, n-type MOS transistors are used. The differential transistors 36a and 36b have drains connected to a power source (VDD) via load resistors 37a and 37b, and sources connected to two constant current sources including the transistors 32 and 33, respectively. The source sides of the transistors 32 and 33 are grounded (GND).

As described above, the differential amplifier includes two constant current sources including the transistor 32 and the constant current source including the transistor 33. The constant current source transistor 32 is connected to a power supply (VG) that applies a voltage to the gate, and the constant current source transistor 33 is connected to a power supply (VG2) that applies a voltage to the gate via the CR circuit 39 and the resistor 38. )It is connected to the. The CR circuit 39 includes a resistor 35 and a capacitor 35 connected between the gate of the transistor 33 and a resistor 34 having one end connected between the capacitor 35 and the gate of the transistor 33 and the other end grounded (GND). .
When the power is turned on, voltage (VG) and voltage (VG2) are applied to the gates of the transistors 32 and 33, so that the gain of the differential amplifier increases. Over time, the voltage (VG2) applied to the gate of the transistor 33 gradually decreases due to the characteristics of the time constant of the CR circuit. By using the CR circuit 39, a large gain is obtained when the power is turned on, and the gain can be suppressed as time passes.

By increasing the gain of the differential amplifier when the power is turned on, the minute signal amplitude of the SAW resonator 1 in FIG. 1 can be increased in a short time, and after a predetermined time has elapsed, the current flowing through the differential amplifier decreases and the gain is suppressed. It is done. By using such a differential amplifier, it is possible to reduce the time required to start oscillation with a stable amplitude, and it is possible to realize an oscillation circuit that does not collapse the signal waveform by suppressing the circuit gain after stable oscillation. is there.
The oscillation amplitude when the feedback circuit is constituted by the differential amplifier of this embodiment is as shown in FIG. In the prior art, it took about 14 μs to oscillate with a stable amplitude, but when this differential amplifier is used, oscillation starts with a stable amplitude in a shorter time.

Next, Embodiment 5 will be described with reference to FIGS.
FIG. 7 is a circuit diagram of a differential amplifier used in the oscillation circuit of FIG. 1, and FIG. 10 is an oscillation amplitude diagram when a feedback circuit is constituted by the differential amplifier of this embodiment.
The differential amplifier shown in FIG. 7 includes a pair of differential transistors 44a and 44b. As these differential transistors, for example, n-type MOS transistors are used. The differential transistors 44 a and 44 b have drains connected to a power supply (VDD) via load resistors 45 a and 45 b, and sources connected to a constant current source including the transistor 40. The source side of the transistor 40 is grounded (GND).
As described above, the differential amplifier includes a constant current source including the transistor 40. The transistor 40 of the constant current source is connected to a power source (VG) that applies a voltage to the gate via a CR circuit 46 and a resistor 43. The CR circuit 46 includes a resistor 43 and a capacitor 42 connected between the gate of the transistor 40 and a resistor 41 having one end connected between the capacitor 42 and the gate of the transistor 40 and the other end grounded (GND). .

  This differential amplifier is characterized in that the gain is changed using a CR circuit 46 including a resistor 41 and a capacitor 42. The voltage (VG) applied to the gate of the transistor 40 is increased when the power is turned on, and thereafter gradually decreased using the characteristics of the time constant of the CR circuit 46. By using the CR circuit 46, a large gain can be obtained when the power is turned on, and the gain can be suppressed as time passes.

By increasing the gain of the differential amplifier when the power is turned on, the minute signal amplitude of the SAW resonator 1 in FIG. 1 can be increased in a short time, and after a predetermined time has elapsed, the current flowing through the differential amplifier decreases and the gain is suppressed. It is done. By using such a differential amplifier, it is possible to reduce the time required to start oscillation with a stable amplitude, and it is possible to realize an oscillation circuit that does not collapse the signal waveform by suppressing the circuit gain after stable oscillation. is there.
The oscillation amplitude when the feedback circuit is constituted by the differential amplifier of this embodiment is as shown in FIG. In the prior art, it took about 14 μs to oscillate with a stable amplitude, but when this differential amplifier is used, oscillation starts with a stable amplitude in a shorter time.
In the above embodiment, an n-type MOS transistor is used as the transistor. However, the present invention is not limited to this, and a p-type MOS transistor can be used. Bipolar transistors can also be used.

The circuit diagram of the oscillation circuit provided with the SAW resonator of the present invention. The circuit diagram of the differential amplifier used for the oscillation circuit of FIG. The circuit diagram of the switch used for the differential amplifier of FIG. FIG. 3 is a circuit diagram of a differential amplifier according to a second embodiment that is used in the oscillation circuit of FIG. 1. FIG. 6 is a circuit diagram of a differential amplifier according to a third embodiment used in the oscillation circuit of FIG. 1. FIG. 6 is a circuit diagram of a differential amplifier according to a fourth embodiment used in the oscillation circuit of FIG. 1. FIG. 6 is a circuit diagram of a differential amplifier according to a fifth embodiment used in the oscillation circuit of FIG. 1. FIG. 3 is an oscillation amplitude diagram when a feedback circuit is configured by the differential amplifier of FIG. 2. FIG. 7 is an oscillation amplitude diagram when a feedback circuit is configured by the differential amplifier of FIG. 6. FIG. 8 is an oscillation amplitude diagram when a feedback circuit is configured by the differential amplifier of FIG. 7. The oscillation amplitude figure when a feedback circuit is comprised with the conventional differential amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... SAW resonator 2, 3, 4, 5 ... Differential amplifier 6, 7, 8, 9, 35, 42 ... Capacitance 10a, 10b ... Bipolar transistor 11 ... Feedback loop 12 ... Terminal resistors 13, 14, 22, 27, 32, 33, 40 ... Constant current source transistors 15, 18a, 18b, 25a, 25b ... Switches 16a, 16b, 21a, 21b, 26a, 26b, 36a, 36b, 44a, 44b ... Differential transistors 17a, 17b, 19a, 19b, 20a, 20b, 23a, 23b, 24a, 24b, 37a, 37b, 45a, 45b ... Load resistance 28, 29,.・ Switching transistor 30 ... Inverter 31,34,38,41,43 ... Resistance 39,46 ... CR circuit

Claims (9)

A resonator, and a differential amplifier that amplifies and outputs a signal generated by the resonator and outputs a feedback signal to the resonator, and a predetermined time after the power is turned on and after the predetermined time has elapsed An oscillation circuit comprising means for changing the gain of the differential amplifier. 2. The oscillation circuit according to claim 1, wherein the differential amplifier makes a gain after the predetermined time has elapsed smaller than a gain at the predetermined time from power-on. 3. The differential amplifier includes a pair of load resistors whose one ends are connected to a first power supply, a pair of differential transistors connected to the other ends of the pair of load resistors, and currents of the pair of differential transistors 3. The oscillation circuit according to claim 1, further comprising: a gain adjustment circuit configured to change a gain of the differential amplifier between the common connection at the outflow end and the second power source. The gain adjustment circuit includes a first transistor and a second transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power source, and the first transistor A constant voltage source connected to the control terminal; and a switch connected to the control terminal of the second transistor and conducting the second transistor to the constant voltage source or the second power source. The control terminal of the second transistor is made conductive to the constant voltage source for a predetermined time from the time point, and the control terminal of the second transistor is made conductive to the second power source after the predetermined time has elapsed. The oscillation circuit according to claim 3, wherein the oscillation circuit is switched. The gain adjustment circuit controls a first transistor and a second transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power source, and controls the first transistor. A first constant voltage source connected to an end; a second constant voltage source for supplying a voltage to the second transistor; and the second constant voltage source between the second transistor and the second constant voltage source. The oscillation circuit according to claim 3, further comprising a CR circuit for limiting a voltage supplied to the two transistors. The gain adjustment circuit includes: a transistor connected between a common connection portion at a current outflow end of the pair of differential transistors and a second power supply; and a first constant voltage that supplies a first voltage to the transistor. A source, a second constant voltage source for supplying a second voltage to the transistor, and between the first constant voltage source and the transistor and between the second constant voltage source and the transistor. 4. The oscillation circuit according to claim 3, further comprising: a CR circuit that controls a voltage supplied to the transistor within a range from the first voltage to the second voltage. 5. The differential amplifier includes the pair of differential transistors, and a plurality of load resistors connected in parallel between current inflow ends of the first power source and the pair of differential transistors, and the load resistors 3. The gain of the differential amplifier is changed by controlling a load resistance value between the first power source and the pair of differential transistors by turning on and off a switch connected in series. Oscillation circuit. The differential amplifier includes the pair of differential transistors and a plurality of load resistors connected in series between current inflow ends of the first power source and the pair of differential transistors, respectively. The gain of the differential amplifier is changed by controlling the load resistance value between the first power supply and the pair of differential transistors by turning on and off a switch connected in parallel with the load resistance between both terminals of The oscillation circuit according to claim 1 or 2, wherein The oscillation circuit according to claim 3, wherein the differential amplifier includes an inductor instead of the load resistor.

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