JPH11330921A - Voltage-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the voltage-controlled oscillator which eases the temperature dependency of a limit oscillation frequency. SOLUTION: Pch transistors(TR) 12a to 12e and Nch TRs 13a to 13e are provided with, Pch TRs 21a to 21e and Nch TRs 22a to 22e for varying current supply capability and the driving capability is detected from the temperature of the Pch TRs to control whether the Pch TRs 21a to 21e and Nch TRs 22a to 22e are made effective or ineffective; when the temperature is high and the driving capability is low, the driving capability can be increased and the temperature dependency of the limit oscillation frequency is eased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator used in a phase locked loop.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram showing a conventional phase locked loop. In FIG. 1, reference numeral 1 designates an external input clock input from the outside and an output from a voltage controlled oscillator 4 arbitrarily by a frequency divider 5. A phase frequency comparator (hereinafter, referred to as PFD) that compares the phase and frequency with the frequency-divided clock, 2 is a charge pump (hereinafter, referred to as CP) that generates a voltage corresponding to the output from PFD 1, and 3 is a resistor. And a capacitor, and a low-pass filter (hereinafter referred to as an LPF) for stabilizing the voltage generated by CP2.
A voltage-controlled oscillator (hereinafter referred to as a VCO) that outputs an oscillation frequency corresponding to the control voltage using the output from the VCO as a control voltage, and 5 externally divides or multiplies the oscillation frequency from the VCO 4 arbitrarily. This is a frequency divider that generates a clock synchronized with the input clock.

FIG. 7 is a circuit diagram showing a conventional voltage controlled oscillator. In the figure, reference numerals 11a to 11e denote inverters in which a Pch transistor and an Nch transistor are paired, and FIG. 7 shows a five-stage inverter circuit. It is.
The input and output of each of the inverters 11a to 11e are connected in a ring to form a ring oscillator.
Reference numerals 12 and 13 denote Pch transistors and Nch transistors for supplying the control voltage Vcnt, and 14 denotes an Nch transistor for changing the frequency control range. 12a-12
e is provided on the power supply side of each of the inverters 11a to 11e,
Pch transistors 13a to 13e that operate according to the control voltage Vcnt are provided on the ground side of the inverters 11a to 11e, and operate according to the control voltage Vcnt.
channel transistors 14a to 14e are connected to each inverter 11
Nch, which is provided on the ground side of a to 11e and operates by power supply, and changes the frequency control range by increasing the current supplied to each of inverters 11a to 11e.
It is a transistor.

Next, the operation will be described. In FIG. 7, when the control voltage Vcnt is low, the Nch transistor 13
a to 13e are almost off, and the inverter 11a
To 11e, the control voltage Vcnt
Is high, the Nch transistors 13a to 13e are turned on, and the current supply to the inverters 11a to 11e increases. The same applies to the Pch transistors 12a to 12e. Here, as the current supply to the inverters 11a to 11e increases, the output waveforms of the inverters 11a to 11e become more agile, and as a result, the oscillation frequency also increases. As described above, the output oscillation frequency of the VCO is uniformly determined by the value of the control voltage Vcnt, and the control voltage Vcnt
The higher the value, the higher the oscillation frequency.

FIG. 6 is a characteristic diagram showing the control voltage Vcnt-output oscillation frequency fOSC characteristic. As described above, the output oscillation frequency fOSC increases as the control voltage Vcnt increases. The oscillation frequency (value at which the characteristic is flat as shown in the right part of FIG. 6) is greatly different. This is because the higher the temperature, the larger the resistance component of the transistor, and the lower the driving capability.

[0006]

Since the conventional voltage controlled oscillator is configured as described above, a phase locked loop (hereinafter, referred to as a PLL circuit) using the VCO 4 as shown in FIG. 1 is optional. Can be generated, which naturally has the premise that the frequency can be oscillated by the VCO 4. As described above, since the VCO 4 has the characteristic that the critical oscillation frequency greatly differs depending on the temperature, it is necessary to sufficiently consider the temperature margin for the desired frequency. However, if that is the case, it is not always possible to take a sufficient margin. If the limit oscillation frequency is designed to be high, for example, by reducing the number of stages of the inverters 11a to 11e or increasing the drive capability of the inverters 11a to 11e, the slope of the arrow portion of the characteristic shown in FIG. The output oscillation frequency fOSC greatly changes due to a slight swing. In other words, the PFD 1 has an adverse effect such that the following characteristic when synchronizing with an external input clock is deteriorated, and an adverse effect such as unnecessary current consumption occurs when the drive capability of the inverters 11a to 11e is higher than necessary. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a voltage-controlled oscillator that alleviates the temperature dependence of a limit oscillation frequency.

[0008]

SUMMARY OF THE INVENTION A voltage controlled oscillator according to the present invention includes a drive capability detection circuit for detecting a decrease in drive capability of a transistor of each inverter due to a rise in temperature, and a transistor in response to the detection of the decrease in drive capability. And a drive capability control circuit for increasing the drive capability of the drive.

A voltage controlled oscillator according to the present invention is provided on a power supply side and a ground side of each inverter, and in parallel with each first power supply transistor, a second power supply transistor which operates according to a control voltage, and a second power supply transistor. (2) A switch provided between the power supply transistor and each inverter, and a drive capability detection circuit for closing each switch in response to a decrease in the drive capability of the transistor due to a rise in temperature.

A voltage-controlled oscillator according to the present invention is provided between a first ring oscillator and a second ring oscillator, and between an output of a last-stage inverter of the first ring oscillator and an input of a first-stage inverter of the second ring oscillator. A first switch; a second switch provided between a first feedback circuit of the first ring oscillator and a second feedback circuit of the second ring oscillator; A third switch provided between the first feedback circuit and the first feedback circuit;
And a drive capability detection circuit for closing the switch.

A voltage controlled oscillator according to the present invention is connected to a drive capacity detection circuit, a series circuit of a drive capacity detection transistor and a resistor, and connected to a connection point of the series circuit. And a first inverter circuit having an operation point at a point where the capacity decreases.

In the voltage controlled oscillator according to the present invention, the driving capability detection circuit uses the control voltage value, the characteristic of which changes as the driving capability of the transistor decreases due to temperature rise in the control voltage-output oscillation frequency characteristic, as an operating point, And a second inverter circuit that operates when the control voltage value is reached.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a phase locked loop according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 designates an external input clock input from the outside and an output from a voltage controlled oscillator 4 by a frequency divider 5 as desired. A phase frequency comparator (hereinafter, referred to as PFD) for comparing the phase and frequency with the clock divided by 2 is a charge pump (hereinafter, referred to as CP) that generates a voltage corresponding to the output from PFD1.
3) is composed of a resistor and a capacitor, and is a low-pass filter (hereinafter, LP) for stabilizing the voltage generated by CP2.
4 is the output from CP2 as the control voltage,
A voltage controlled oscillator (hereinafter referred to as a VCO) 5 which outputs an oscillation frequency corresponding to the control voltage, 5 is a clock synchronized with an external input clock by arbitrarily dividing or multiplying the oscillation frequency from the VCO 4 Is generated by the frequency divider.

FIG. 2 is a circuit diagram showing a voltage controlled oscillator according to the first embodiment of the present invention.
Reference numeral 11e denotes an inverter in which a Pch transistor and an Nch transistor are paired. In the drawing, three intermediate stages are omitted from the five-stage inverter circuit. Also,
The input and output of each of the inverters 11a to 11e are connected in a ring to form a ring oscillator. 12,
13 is a Pch transistor and an Nch transistor for supplying the control voltage Vcnt, and 14 is an Nch transistor for changing the frequency control range. 12a to 12e are provided on the power supply side of each of the inverters 11a to 11e, and operate according to the control voltage Vcnt.
Power supply transistors), 13a to 13e are provided on the ground side of each of the inverters 11a to 11e, and control voltage Vcn
The Nch transistors (first power supply transistors) 14a to 14e which operate according to the respective inverters 11a
Ne, which are provided on the ground side of the inverters 11a to 11e, operate by power supply, and change the frequency control range by increasing the current supplied to each of the inverters 11a to 11e.
It is a transistor. Also, 21a to 21e are provided on the power supply side of each of the inverters 11a to 11e, and each Pch
A Pch transistor (the second transistor) is provided in parallel with the transistors 12b to 12e and operates according to the control voltage Vcnt.
Power supply transistors), 22a to 22e are provided on the ground side of the inverters 11a to 11e and provided in parallel with the Nch transistors 13b to 13e, and are Nch transistors (second power supply transistors) that operate according to the control voltage Vcnt. ), 23a to 23e are inverters 1
A transmission gate (switch) provided between 1a to 11e and Pch transistors 21a to 21e;
24a to 24e are transmission gates (switches) provided between the inverters 11a to 11e and the Nch transistors 22a to 22e, and 25a to 25e are inverter circuits for inputting a control signal a. The Pch transistors 21a to 21e and the Nch transistors 22a to 22e
22e and transmission gates 23a-23
e, 24a to 24e constitute a drive capacity control circuit.

FIG. 3 is a circuit diagram showing a drive capability detecting circuit according to the first embodiment of the present invention.
1 is a Pch transistor (drive capability detection transistor) for detecting the drive capability due to temperature rise, 32 is a resistor (drive capability detection circuit) connected in series to the Pch transistor 31, and 33 is the drive capability of the Pch transistor 31 due to temperature rise. Is an inverter circuit (first inverter circuit) having an operating point at the point of decrease. Also,
Reference numerals 34 to 38 denote latch circuits for latching the output of the inverter circuit 33 at the time of reset release, 34 denotes an Nch transistor, 35 to 38 denote inverter circuits, and 39 and 40 denote transmission gates.

Next, the operation will be described. In FIG. 2, Pch transistors 21a to 21e and Nch transistors 22a to 22e are added as compared with FIG.
And for changing the current supply capability (drive capability of the inverter) of the Nch transistors 13a to 13e. Also, the transmission gate 23a
To 23e and 24a to 24e are configured to be opened and closed by a control signal a. This control signal a is an output from the drive capability detection circuit shown in FIG.
"H" when the temperature rises and the drive capacity decreases
Is output. This control signal a is "H"
When the transmission gate 23
a to 23e and 24a to 24e are closed, and the Pch transistors 21a to 21e and the Nch transistor 2
Since 2a to 22e become effective, the Pch transistor 1
2a to 12e and Nch transistors 13a to 13e
Current supply capability. Conversely, control signal a
Is input at "L", the transmission gates 23a to 23e and 24a to 24e are opened,
Since the Pch transistors 21a to 21e and the Nch transistors 22a to 22e become invalid, the Pch transistors 12a to 12e and the Nch transistor 13a
The current supply capacity is only 13e. This allows
When the temperature is high and the drive capacity is reduced, the effect that the drive capacity can be increased is obtained.

Next, the operation of the drive capability detection circuit shown in FIG. 3 will be described. This drive capability detection circuit has a configuration in which the drive capability based on the temperature of the Pch transistor 31 is detected to generate a control signal a.
When the drive capability of the channel transistor 31 decreases, the on-resistance of the Pch transistor 31 increases, and the voltage input to the inverter circuit 33 decreases due to resistance division with the resistor 32. The inverter circuit 33 outputs “H” when the input voltage value is lower than the threshold value of the inverter circuit 33. The latter stage is a latch circuit that latches the output of the inverter circuit 33 when the reset is released, and the drive capability is detected only when the reset is released. This is to prevent the frequency from changing during the operation of the PLL circuit. The Nch transistor 34 is inserted to determine the initial value (at the time of reset) of the latch circuit. In this way, when the drive capacity is reduced by the inverter circuit 38, the control signal a of "H" can be output.

In the first embodiment, one inverter circuit 33 and one parallel transistor are provided, and it is determined whether the one parallel transistor is enabled or disabled depending on whether the driving capability based on temperature is high or low. Although the control is performed, if a plurality of inverter circuits and a plurality of parallel transistors are provided, and the drive capability according to temperature is divided in stages to control whether to enable or disable the plurality of parallel transistors in stages, furthermore, Fine control can be realized. Further, in the first embodiment, the parallel transistors are provided for all the power supply transistors, but the parallel transistors may be provided partially according to the control conditions.

As described above, according to the first embodiment, Pch transistors 12a to 12e and Nch transistors 13a to 13e are provided with Pch transistors 21a to 21e and Nch transistors for changing the current supply capability.
Transistors 22a to 22e are provided to detect the drive capability of the Pch transistor 31 depending on the temperature, and to control whether the Pch transistors 21a to 21e and the Nch transistors 22a to 22e are enabled or disabled by a control signal a. Therefore, when the temperature is high and the driving capability is lowered, the driving capability can be increased, and the inclination of the arrow portion of the control voltage Vcnt-output oscillation frequency fOSC characteristic shown in FIG. The tracking characteristic when synchronizing with an external input clock by the PFD 1 is improved.
The effect is obtained that the current consumption by a to 11e can be prevented from becoming unnecessarily high.

Embodiment 2 FIG. 4 is a circuit diagram showing a voltage controlled oscillator according to a second embodiment of the present invention. In the figure, reference numerals 11a to 11g denote inverters each of which is a pair of a Pch transistor and an Nch transistor. A first ring oscillator is configured, and a second ring oscillator is configured by the inverters 11f and 11g. 12a to 12g are each inverter 1
Pch transistors (first power supply transistors) which are provided on the power supply side of 1a to 11g and operate according to the control voltage Vcnt, 13a to 13g are inverters 11a to 1g, respectively.
Nch transistors (first power supply transistors) 14a to 14g, which are provided on the ground side of 1g and operate according to the control voltage Vcnt, are provided on the ground side of the inverters 11a to 11g, operate by power supply, An Nch transistor that changes the frequency control range by increasing the current supplied to 11a to 11g. 41 is a first feedback circuit, 42 is a second feedback circuit, 43a is a transmission gate (first switch) provided between the output of the last-stage inverter 11e and the input of the first-stage inverter 11f, and 43b is A transmission gate (second switch) provided in the second feedback circuit 42, a transmission gate (third switch) 43c provided in the first feedback circuit 41, and an inverter circuit 44 for inverting the control signal a are provided. It is. Inverter 1
1f, 11g, Pch transistors 12f, 12g, N
The drive capability control circuit is constituted by the channel transistors 13f and 13g, the transmission gates 43a to 43c, and the inverter circuit 44.

Next, the operation will be described. In FIG. 4, when the control signal a is "L", the transmission gates 43a to 43c
a, 43b are closed, transmission gate 43c
Is open, and the second feedback circuit 42 is selected.
When the control signal a is "H", the opposite is true, the transmission gates 43a and 43b are open, the transmission gate 43c is closed, and the first feedback circuit 41 is selected. That is, when the temperature is high and the drive capability is reduced, the control signal a is "H", and the effect is obtained that the number of stages of the ring oscillator decreases and the limit starting frequency is increased.

In the second embodiment, the number of stages of the ring oscillator is increased or decreased. However, any number of even stages may be used depending on the control conditions. Embodiment 1
However, as described above, finer control can be realized by controlling the number of stages of the ring oscillator to be increased or decreased stepwise by dividing the drive capability according to the temperature stepwise.

As described above, according to the second embodiment, the inverters 11f, 11g, the Pch transistor 1
2f, 12g, Nch transistors 13f, 13g, 1
4f, 14g, transmission gates 43a to 43
(c) A drive capacity control circuit is constituted by the inverter circuit 44, and when the temperature is high and the drive capacity is reduced, the number of stages of the ring oscillator is reduced. If
The drive capability can be increased, the inclination of the arrow portion of the control voltage Vcnt-output oscillation frequency fOSC characteristic shown in FIG. 6 does not increase, and the tracking characteristic when synchronizing with the external input clock is improved by the PFD1. In addition, it is possible to prevent the current consumption of the inverters 11a to 11e from being unnecessarily high.

Embodiment 3 FIG. FIG. 5 is a circuit diagram showing a drive capability detection circuit according to Embodiment 3 of the present invention.
In the figure, reference numeral 51 denotes an operation point at which a control voltage value whose characteristic changes due to a decrease in the drive capability of a transistor due to a rise in temperature in a control voltage-output oscillation frequency characteristic is an operation point, and an inverter that operates when the control voltage reaches the control voltage value Circuit (second inverter circuit). The other configuration is the same as the configuration shown in FIG. 3 of the first embodiment, so that the same reference numerals are given and the duplicate description will be omitted.

Next, the operation will be described. FIG. 5 is different from FIG. 3 in that the detection of the drive capability is performed by the control voltage Vcnt. As can be seen from the control voltage Vcnt-output oscillation frequency fOSC characteristic in FIG. 6, the characteristic has no temperature dependence until the control voltage Vcnt is near the arrow range, whereas the control voltage Vcnt is higher than the arrow range. It utilizes the property that the temperature dependence of the characteristics increases when the size increases. FIG.
In, the operating point of the inverter circuit 51 is set to the control voltage Vcnt at which the temperature dependence of the characteristic becomes large. When the control voltage Vcnt reaches the operating point, the inverter circuit 51 outputs “L” and outputs “L” as the control signal a. Therefore, the transmission gates 23a to 23e and 24a to 24 in FIGS.
e, the transmission gates 43a to 43c are set so as to operate in the opposite manner to the operation described in the first and second embodiments. Thus, there is an effect that the drive capability detection circuit can be realized with a simple configuration.

In the third embodiment, one inverter circuit 51 is provided. However, a plurality of inverter circuits that operate stepwise according to a change in the control voltage Vcnt may be provided.

As described above, according to the third embodiment, the drive capability detection circuit is controlled by the inverter whose operating point is set to the control voltage Vcnt at which the temperature dependence of the control voltage-output oscillation frequency characteristic becomes large. The configuration using the circuit 51 has an effect that the drive capability detection circuit can be realized with a simple configuration.

[0028]

As described above, according to the present invention, there is an effect that the drive capability of the transistor is increased in response to the detection of the decrease in drive capability, and the temperature dependence of the limit oscillation frequency can be reduced.

According to the present invention, the second power supply transistor can be made effective in response to a decrease in the drive capability of the transistor due to a rise in temperature, the drive capability can be increased, and the temperature dependence of the limit oscillation frequency can be reduced. There is an effect that can be done.

According to the present invention, the second ring oscillator is disconnected in response to a decrease in the drive capability of the transistor due to a rise in temperature, and the number of inverter stages is reduced.
There is an effect that the limit oscillation frequency at the time of temperature rise can be increased, and the temperature dependence of the limit oscillation frequency can be reduced.

According to the present invention, it is possible to detect a decrease in the actual drive capability of the transistor by the drive capability detection transistor, and it is possible to realize highly accurate control.

According to the present invention, a decrease in drive capability can be detected only by the second inverter circuit.
There is an effect that can be realized with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional and a phase locked loop according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a voltage controlled oscillator according to Embodiment 1 of the present invention.

FIG. 3 is a circuit diagram showing a drive capability detection circuit according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a voltage controlled oscillator according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a drive capability detection circuit according to a third embodiment of the present invention.

FIG. 6 shows control voltage Vcnt-output oscillation frequency fOSC
It is a characteristic view showing a characteristic.

FIG. 7 is a circuit diagram showing a conventional voltage controlled oscillator.

[Explanation of symbols]

11a-11e Inverter (first ring oscillator), 11f, 11g Inverter (drive capacity control circuit, second ring oscillator), 12a-12ePch
Transistors (first power supply transistors), 12f,
12g Pch transistor (drive capacity control circuit,
1st power supply transistor), 13a to 13e Nch
Transistors (first power supply transistors), 13f,
13g Nch transistor (drive capacity control circuit,
1st power supply transistor), 21a-21e Pch
Transistors (drive capacity control circuit, second power supply transistor), 22a to 22e Nch transistors (drive capacity control circuit, second power supply transistor), 23a to 23e, 24a to 24e Transmission gates (drive capacity control circuit, switch) , 31
Pch transistor (drive ability detection circuit, drive ability detection transistor), 32 resistor (drive ability detection circuit), 33 inverter circuit (drive ability detection circuit, first inverter circuit), 41 first feedback circuit,
42 second feedback circuit, 43a transmission gate (drive capacity control circuit, first switch), 43b transmission gate (drive capacity control circuit, second switch)
Switch 43g, transmission gate (drive capacity control circuit, third switch), 44 inverter circuit (drive capacity control circuit), 51 inverter circuit (drive capacity detection circuit, second inverter circuit).

Claims (5)

[Claims] 1. A ring oscillator in which the input and output of each of a plurality of inverters each comprising a transistor are connected in a ring shape, and a first power supply provided on each of a power supply side and a ground side of each of the inverters and operated according to a control voltage. A supply transistor, and a drive capability detection circuit that detects a decrease in drive capability of the transistor due to a rise in temperature,
A voltage controlled oscillator comprising: a drive capability control circuit that increases the drive capability of the transistor in response to detection of a decrease in drive capability by the drive capability detection circuit. 2. A ring oscillator in which the input and output of each of a plurality of inverters composed of transistors are connected in a ring shape, and a first power supply provided on each of a power supply side and a ground side of each of the inverters and operated according to a control voltage. A supply transistor, a second power supply transistor provided on each of the power supply side and the ground side of each of the inverters and in parallel with each of the first power supply transistors, and operated in accordance with a control voltage, and each of the second power supply transistors And a drive capacity detection circuit that closes each of the switches in response to a decrease in the drive capacity of the transistor due to a rise in temperature. Voltage controlled oscillator. 3. A first ring oscillator in which the input and output of each of a plurality of inverters formed of transistors are connected in a ring, and a second ring in which the input and output of each of a plurality of inverters formed of transistors are connected in a ring. An oscillator, a first power supply transistor provided on each of a power supply side and a ground side of each of the inverters of the first and second ring oscillators and operated according to a control voltage, and an output of a last-stage inverter of the first ring oscillator; A first switch provided between the input of the first-stage inverter of the second ring oscillator and a first switch provided between the first feedback circuit of the first ring oscillator and the second feedback circuit of the second ring oscillator; The second switch, and the first switch
The output of the last-stage inverter of the ring oscillator and the first
A third switch provided between the first switch and the feedback circuit; and a drive for opening the first and second switches and closing the third switch in response to a decrease in the drive capability of the transistor due to a rise in temperature. A voltage controlled oscillator including a capability detection circuit. 4. A drive capacity detection circuit is connected to a series circuit of a drive capacity detection transistor and a resistor, and is connected to a connection point of the series circuit, and operates a drop point of the drive capacity of the drive capacity detection transistor due to a rise in temperature. The voltage controlled oscillator according to any one of claims 1 to 3, further comprising a first inverter circuit serving as a point. 5. The drive capability detection circuit sets an operation point to a control voltage value at which characteristics of a control voltage-output oscillation frequency characteristic change due to a decrease in drive capability of a transistor due to a rise in temperature, and the control voltage reaches the control voltage value. The voltage controlled oscillator according to any one of claims 1 to 3, further comprising a second inverter circuit that operates when the voltage is controlled.