JP2005191625A - Oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillation circuit which increases the capability of driving its oscillation element in an operating state wherein reduction in the capability of driving the oscillation element due to heat generation is estimated, and reduces the power consumption of the oscillation circuit by suppressing the capability of driving the oscillation element in a backup operating state by a secondary battery not causing the heat generation, in a semiconductor device used for a system such as a mobile phone and a PDA and provided with: a constant voltage output circuit; a circuit such as a speaker amplifier needing large power consumption and causing high heat generation; and the oscillation circuit for generating a real time clock and its reference clock. <P>SOLUTION: The oscillation circuit switches the capability of driving the oscillation element at a time constant and controls switching of the driving capability by switching a drive current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a constant voltage output circuit used in a system such as a cellular phone or a PDA, a circuit that generates large amounts of power, such as a speaker amplifier, and a semiconductor device including an oscillation circuit that generates a real-time clock and its reference clock. Increase the ability to drive the oscillator of the oscillation circuit in the operating state where the ability to drive the child is expected to decrease, and suppress the ability to drive the oscillator in the backup operation state with a secondary battery that does not generate heat. The present invention relates to an oscillation circuit that can reduce the power consumption of the oscillation circuit.

  In systems such as mobile phones and PDAs, a semiconductor device that combines a constant voltage output circuit, a speaker amplifier and other circuits that generate large amounts of power consumption, a real-time clock that operates with low power consumption, and an oscillation circuit that generates its reference clock. It has. In such a system, the operation mode of the primary battery, in which all the circuits are expected to operate and generate heat, only the oscillation circuit that generates the real-time clock and its reference clock operates, the heat generation is very small, and the temperature is almost the same as the ambient temperature. There are two operation states of the operation mode by the secondary battery, and it is necessary to obtain stable oscillation in both operation states.

  Such a technique is disclosed in Patent Document 1.

  Hereinafter, a conventional oscillation circuit will be described with reference to the drawings.

  FIG. 6 shows a configuration of a conventional oscillation circuit.

  In FIG. 6, 100 is a power supply terminal, 110 is a PchMOS transistor (hereinafter referred to as PchMOS), 120 is an NchMOS transistor (hereinafter referred to as NchMOS), 130 is a feedback resistor, 140 is a load capacitor, 150 is a load capacitor, 160 is an output terminal, and 170 is a vibrator. It is.

  The source of the PchMOS 110 is connected to the power supply terminal 100, the drain of the PchMOS 110 is connected to the drain of the NchMOS 120, the source of the NchMOS 120 is grounded, and the gates of the PchMOS 110 and the NchMOS 120 are connected. Furthermore, the gate connected to PchMOs 110 and NchMOS 120 is connected to feedback resistor 130, load capacitor 140, and vibrator 170, and the drain connected to PchMOS 110 and NchMOS 120 is the other end of feedback resistor 130, and the other of load capacitor 150 and vibrator 170. One end is connected. The other ends of the load capacitor 140 and the load capacitor 150 are grounded. The output of the circuit thus connected is taken out from the output terminal 160.

  The operation of the oscillation circuit configured as described above will be described below.

When the power supply 100 is applied, the gate to which the PchMOS 110 and the NchMOS 120 are connected is in a discharge state due to leakage or the like, so that it is at ground potential and the PchMOS operates and the potential at which the PchMOS 110 and NchMOS 120 are connected through the feedback resistor 130 give. The resonance circuit composed of the vibrator 170, the load capacitor 140, and the load capacitor 150 is similarly supplied with current from the Pch MOS 110, and starts oscillating operation by the inverter circuit composed of the Pch MOS 110 and the Nch MOS 120 to which a DC operating point is given. Then, an oscillation output can be obtained at the output end 160.
Japanese Patent Laid-Open No. 01-62904

  However, in the conventional configuration, the ability to drive the resonance circuit is determined by the element sizes of the PchMOS 110 and the NchMOS 120, and the oscillation margin is determined. As an oscillation circuit used for a semiconductor device with a built-in real-time clock circuit that requires a minimum power consumption in the secondary battery operation mode because it is necessary to determine the element size on the assumption that the current consumption always increases. It becomes a problem.

  FIG. 7 is an operation state diagram of a conventional oscillation circuit.

  In the conventional circuit, when the PchMOS 110 and the NchMOS 120 are complementary, an oscillation operation is performed with the midpoint of the power supply voltage as the DC operating point. In an operating state where the semiconductor device generates heat and becomes high temperature, the on-resistance is increased and the current consumption is reduced, so that the oscillation margin is lowered. For this reason, the elements constituting the inverter circuit are configured in advance so as to obtain a drive current capable of obtaining stable oscillation even at a high temperature.

  The present invention solves the above-described conventional problems, and is a constant voltage output circuit used in a system such as a mobile phone or a PDA, a circuit that generates a large amount of power, such as a speaker amplifier, a real-time clock, and an oscillation that generates its reference clock In a semiconductor device having a circuit, in an operation state in which the ability to drive an oscillator is reduced due to heat generation, the ability to drive the oscillator of the oscillation circuit is increased, and in a backup operation state by a secondary battery that does not generate heat. An object of the present invention is to provide an oscillation circuit capable of reducing the power consumption of the oscillation circuit by suppressing the ability to drive the oscillator.

  In order to achieve this object, the present invention is characterized in that the driving ability of the oscillator is switched with a time constant.

  With this configuration, stable oscillation is obtained both in an operation state in which the ability to drive the oscillator due to heat generation is expected to be reduced and in a backup operation state by a secondary battery that does not generate heat, and when the secondary battery is used, the oscillation circuit Current consumption can be reduced.

  According to the present invention, by switching the driving ability of the oscillator, stable oscillation can be obtained both in an operation state in which the ability to drive the oscillator is reduced due to heat generation and in a backup operation state by a secondary battery that does not generate heat. In addition, when using a secondary battery, the current consumption of the oscillation circuit can be reduced, and a change in the DC operating point can be provided by providing a time constant for switching, resulting in a sudden change in the DC operating point. An oscillation circuit that avoids temporary oscillation stop is realized.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of an oscillation circuit according to an embodiment of the present invention.

  In FIG. 1, 100 is a power supply terminal, 110 is a PchMOS transistor (hereinafter referred to as PchMOS), 120 is an NchMOS transistor (hereinafter referred to as NchMOS), 130 is a feedback resistor, 140 is a load capacitor, 150 is a load capacitor, 160 is an output terminal, and 170 is a vibrator. , 180 is an Nch MOS transistor, 200 is a current source circuit, and 210 is a capacitor.

  The source of the PchMOS 110 is connected to the power supply terminal 100, the drain of the PchMOS 110 is connected to the drain of the NchMOS 120, the source of the NchMOS 120 is grounded, the gate of the NchMOS 120 is connected to the current source 200, the capacitor 210, and the gate and drain of the NchMOS 180. The NchMOS 120 and NchMOS 180 constitute a current mirror circuit by grounding the source. The other end of the capacitor 210 is grounded. Further, the gate of the PchMOS 110, the feedback resistor 130, the load capacitor 140, and the vibrator 170 are connected, and the other end of the feedback resistor 130, the load capacitor 150, and the other end of the vibrator 170 are connected to the drain connected to the PchMOS 110 and the NchMOS 120. . The other ends of the load capacitor 140 and the load capacitor 150 are grounded. The output of the circuit thus connected is taken out from the output terminal 160.

  The operation of the oscillation circuit configured as described above will be described below.

  When the power supply 100 is applied, since the gate of the PchMOS 110 is in a discharge state due to leakage or the like, it is at the ground potential, the PchMOS operates, and a potential serving as a DC operating point is given to the gate of the PchMOS 110 through the feedback resistor 130. The current source 200 charges the capacitor 210 and supplies a current to a current mirror circuit constituted by the Nch MOS 180 and the Nch MOS 120. Further, the resonance circuit composed of the vibrator 170, the load capacitor 140, and the load capacitor 150 is similarly provided with a current from the PchMOS 110, and includes a PchMOS 110 to which a DC operating point is given and an NchMOS 120 that drives a current determined by the current source 200. The oscillating operation is started by the inverter circuit, and an oscillation output can be obtained at the output terminal 160.

  In this circuit configuration, by increasing / decreasing the current value of the current source 200, the same effect as increasing / decreasing the element sizes of the PchMOS 110 and the NchMOS 120 constituting the inverter circuit of the conventional invention can be obtained.

  Therefore, it is possible to easily change the driving capability of the oscillation circuit by changing the value of the current source 200 as necessary. Also, if the current value of the NchMOS 120 changes, the DC operating point as an inverter changes, so there is a risk that oscillation will temporarily stop when changing the driving capability. In this circuit configuration, the current value of the current source 200 is caused by the action of the capacitor 210. Because the current change of the current mirror circuit consisting of NchMOS 180 and NchMOS 120 has a time constant when changing dc, the change in the DC operating point also has a time constant and avoids temporary oscillation stop due to sudden fluctuation of the DC operating point can do.

  2A and 2B are operation state diagrams of the present invention.

  The drive current is efficiently set according to the operation state of the semiconductor device by the control signal. Further, in FIG. 2 (A) when the switching of the driving current is not performed, the oscillation may stop when the DC operating point fluctuates, but when the time constant is provided, FIG. 2 (B). Thus, stable oscillation can be obtained without causing oscillation stop.

  FIG. 3 is a diagram specifically showing the configuration of the current source 200 in the oscillation circuit of FIG. 1 whose operation has been previously described.

  1, 220 is a resistor, 230 is a resistor, 240 is a PchMOS, and 250 is a control signal input terminal.

  The resistor 220 is connected to the power supply 100, the source of the PchMOS 240 is connected to the power supply 100, the drain of the PchMOS 240 is connected to the resistor 230, one end of the resistor 220 and one end of the resistor 230 are connected, and the current source 200 used in FIG. Constitute. The control signal input terminal 250 is connected to the gate of the Pch MOS 240. Other connections are the same as in FIG.

  In the operation of the oscillation circuit of FIG. 1 described above, the current source 200 is configured by the resistor 220 and the resistor 230, and the PchMOS 240 is turned on / off by the control signal input from the control signal input terminal, thereby connecting the resistor 230. By controlling and changing the current value of the current mirror circuit composed of NchMOS 180 and NchMOS 120, the driving capability of the inverter circuit composed of PchMOS 110 and NchMOS 180 is changed.

  FIG. 4 is a diagram in which the resistor 220 and the resistor 230 are configured by the PchMOS 270 and the PchMOS 280 in the oscillation circuit of FIG.

  PchMOS 270 and PchMOS 280 are used as resistors by grounding their gates. Other connections are the same as in FIG. The operation is the same as that described with reference to FIG.

  FIG. 5 is a diagram in which a resistor 220 and a resistor 230 which are current sources in the oscillation circuit of FIG.

  Reference numeral 300 is a current mirror circuit control voltage input terminal, 310 is a PchMOS, and 320 is a PchMOS.

In operation, the current source 200 is configured by operating the PchMOS 310 and the PchMOS 320 as a current mirror circuit by the potential applied from the current mirror circuit control voltage input terminal.
Other operations are the same as those in FIG.

  It is obvious that the same operation can be obtained even if the PchMOS transistor and the NchMOS transistor are exchanged in the configurations described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.

  According to the present invention, by switching the driving ability of the oscillator, stable oscillation can be obtained both in an operation state in which the ability to drive the oscillator is reduced due to heat generation and in a backup operation state by a secondary battery that does not generate heat. In addition, when using a secondary battery, the current consumption of the oscillation circuit can be reduced, and a change in the DC operating point can be provided by providing a time constant for switching, resulting in a sudden change in the DC operating point. An oscillation circuit that avoids temporary oscillation stop is realized.

1 is a configuration diagram of an oscillation circuit according to an embodiment of the present invention. FIG. 2 is a waveform diagram of a main part of an oscillation circuit according to an embodiment of the present invention. The block diagram of the 2nd oscillation circuit in one embodiment of the present invention The block diagram of the 3rd oscillation circuit in one Embodiment of this invention The block diagram of the 4th oscillation circuit in one embodiment of the present invention Configuration of conventional oscillator circuit Waveform diagram of the main part of a conventional oscillation circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Power supply terminal 110 PchMOS transistor 120 NchMOS transistor 130 Feedback resistance 140 Load capacity 150 Load capacity 160 Output terminal 170 Vibrator 180 NchMOS transistor 200 Current source 210 Capacitor 220 Resistance 230 Resistance 240 PchMOS transistor 250 Control signal input terminal 270 PchMOS transistor 280 PchMOS transistor 300 Current mirror circuit control voltage input terminal 310 PchMOS transistor 320 PchMOS transistor

Claims (5)

An oscillation circuit characterized by switching the driving ability of an oscillator with a time constant. 2. The oscillation circuit according to claim 1, wherein switching of the driving capability is controlled by switching of driving current. 3. An oscillation circuit characterized in that the switching of the drive current according to claim 2 is controlled by switching of a resistor. 3. An oscillation circuit characterized in that the resistor for switching the drive current according to claim 2 is constituted by a MOS transistor. 3. An oscillation circuit characterized in that switching of the drive current according to claim 2 is controlled by switching of a current mirror circuit.

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