JPH10200382A - Voltage controlled oscillator circuit for low voltage driving - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a wide dynamic range for an input control voltage signal in spite of low voltage driving and to reduce frequency fluctuation against the fluctuation of power supply voltage by receiving the control voltage signal, supplying power through an output to a power reception line corresponding to this signal and controlling the oscillation frequency of the oscillation circuit. SOLUTION: An oscillation frequency control circuit 11 is a CMOS type voltage follower, the control voltage signal for controlling the frequency from the outside is inputted by an input terminal 13 connected to the gate of FET Q1 and while connecting the gate of FET Q2 to an output terminal 13b, feedback is performed. Thus, since the output side of the oscillation frequency control circuit 11 is fed back to the input side, the output voltage gets equal with the input voltage, a current value generated on a power reception line Vp becomes a current value corresponding to the control voltage value, power is supplied to a ring oscillator 3 and its frequency is controlled. Thus, the oscillation frequency of the ring oscillator 3 is hardly affected by the fluctuation of power supply voltage.

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 (VCO) driven by a low voltage, and more particularly, to a clock generation in a personal computer, a PLL control loop in a signal processing circuit of an audio device, a video device and the like. The present invention relates to a VCO which has a large dynamic range with respect to an input control voltage signal even when driven at a low voltage, and which is suitable for use in an IC having a small frequency fluctuation with respect to a power supply voltage fluctuation.

[0002]

2. Description of the Related Art Conventionally, in a clock generation of a personal computer, a frequency synthesizer and an FM detection circuit in an audio device, and a video detection circuit and a phase detection circuit in a video device such as a VTR, a PLL built in an IC is used. A VCO is provided in the control loop. FIG. 2 shows an example of the VCO. In the figure, reference numeral 1 denotes a VCO provided inside an IC, which comprises an oscillation frequency control circuit 2 and a ring oscillator 3. In addition, 8
a is a control voltage terminal of the VCO 1, 8b is an output terminal thereof, and 9 is a PLL loop circuit composed of a phase comparison circuit, a low-pass filter, a divider, and the like. The oscillation frequency control circuit 2 is a voltage / current conversion circuit,
A current value corresponding to the control voltage of the input terminal 8a is supplied to the ring oscillator 3. This is a p-type MO with a gate connected.
A current mirror circuit 4 including SFETs 4a and 4b;
An n-type MOSFET 4c provided downstream of the diode-connected MOSFET 4a, and a MOSFET 4b
And an oscillation circuit 3 connected downstream. Note that MO
The source side of the SFETs 4a and 4b has a power supply line VDD.
, The source of the FET 4c is grounded, and the gate thereof receives a control voltage signal via the input terminal 8a.

The ring oscillator 3 comprises a three-stage inverter connected between a power receiving line Vp derived from the drain of the MOSFET 4b and the ground GND. Each inverter has a p-type MOSFET and an n-type MO
CMOS inverter 5, which is stacked and connected with SFET 5,
6, 7 are connected in cascade, and the output terminal 8b (the output terminal of the last-stage inverter 7) is connected to the input terminal of the first-stage inverter 5 on the input side, whereby an oscillation circuit is formed. I have.

FIG. 3 shows another example, in which an n-type MOSFET 4 d is provided between a power supply line VDD and a ring oscillator 3. As described above, the VCO that is formed into an IC is generally configured mainly of a CMOS type in order to reduce power consumption or because a digital circuit is often used as a peripheral circuit.

[0005]

On the other hand, in audio equipment and video equipment such as personal computers, portable type and power saving are progressing, and the power supply voltage is changed from 5V to 3.
It has fallen to 3V and more recently to around 2.5V or 1.8V. When the power supply voltage decreases in this manner, in the VCO configuration of FIG. 2, the gate voltage vs. output current characteristic is affected by the power supply voltage because the voltage / current conversion circuit is constituted by a current mirror, and the power supply voltage is reduced. There is a drawback that a slight variation becomes a large ratio when viewed from the entire power supply voltage, and the variation in the frequency of the ring oscillator is greatly affected by the variation in the power supply voltage. Further, in the VCO configuration of FIG. 3, the dynamic range of the input control voltage signal applied to the input terminal 8a is limited because the voltage drop between the gate and the source acts as much as the power supply voltage is low. The present invention
In order to solve such problems of the prior art,
An object of the present invention is to provide a low-voltage driven VCO that has a large dynamic range with respect to an input control voltage signal and has a small frequency fluctuation with respect to a power supply voltage fluctuation even in a low-voltage driving.

[0006]

A feature of the VCO according to the present invention that achieves the above object is that a plurality of inverters connected to a common power receiving line are connected in a multistage cascade, and the output is fed back to the input. An oscillation circuit that oscillates, and a voltage follower that receives a control voltage signal, supplies power via an output to a power receiving line in response thereto, and controls the oscillation frequency of the oscillation circuit.

[0007]

As described above, the power receiving line for determining the operating voltage of the inverter is output from the voltage follower to drive the oscillation circuit, and the control voltage signal for controlling the frequency is input to the input of the voltage follower. Thereby, power supply of a voltage equal to the control voltage can be supplied to the oscillation circuit to control the oscillation frequency. as a result,
Even in a circuit with a low power supply voltage, the voltage of the control voltage signal can expand the dynamic range to near the power supply voltage, and the oscillation frequency can be controlled in that range. Further, since the operating voltage of the oscillation circuit is determined by the voltage of the control voltage signal, the operating voltage is less affected by the fluctuation of the power supply voltage.

[0008]

FIG. 1 is a circuit diagram of an embodiment to which the VCO of the present invention is applied. Note that components similar to those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. The difference between the VCO 10 of FIG. 1 and that of FIG. 2 is that the oscillation frequency control circuit 2 is replaced by an oscillation frequency control circuit 11. The oscillation frequency control circuit 11 is a so-called CMOS type voltage follower, and a MOSF with a current mirror load.
An ET differential amplifier 12 and a next-stage amplifier 13 receiving the output of the differential amplifier are provided. The output terminal 13 b of the next-stage amplifier 13 is connected to the power receiving line Vp of the ring oscillator 3.

The differential amplifier 12 includes a pair of n-type MOSFETs Q1 and Q2 that perform a differential operation, and current-mirror-loaded p-type MOSFETs Q3 and Q4 provided upstream thereof.
And a constant current source 14 provided downstream thereof, through which the MOSFETs Q1, Q2
Are connected to the ground GND. The sources of the FETs Q3 and Q4, which are loads, are connected to the power supply line VDD. Here, the input of the control voltage signal for controlling the frequency from the outside is the FET Q1
Input terminal 13a connected to the gate of
The gate of the ETQ2 is connected to the output terminal 13b to perform feedback.

The next-stage amplifier 13 comprises a p-type MOSFET Q5 having a source connected to the power supply line VDD side, and a constant current source 15 connected to the drain thereof and provided downstream. The other terminal is connected to the ground GND. The drain of the FET Q5 is connected to the output terminal 13b, and the gate is connected to the drain of the FET Q2.

In the VCO 10 having such a configuration,
Since the output side of the oscillation frequency control circuit 11 is fed back to the input side, the output voltage becomes equal to the input control voltage, the current value generated in the power receiving line Vp becomes a current value corresponding to the control voltage value, and Power is supplied to the oscillator 3 and its frequency is controlled. For this reason, the oscillation frequency of the ring oscillator 3 is hardly affected by the fluctuation of the power supply voltage.
Further, the input control voltage signal applied to the input terminal 13a is changed from the ground level to the voltage −Vsat of the power supply line VDD.
(Saturation voltage at the time of ON between the source and the drain of the FET Q5), so that a large dynamic range can be obtained.

As described above, the present invention is not limited to a circuit mainly having a CMOS configuration as in the embodiment.

[0013]

As described above, according to the present invention, the power receiving line for determining the operating voltage of the inverter is output as a voltage follower to drive the oscillation circuit, and the frequency is controlled to the input of the voltage follower. By inputting the control voltage signal, power supply of a voltage equal to the control voltage can be supplied to the oscillation circuit to control the oscillation frequency. As a result, even in a circuit with a low power supply voltage,
The voltage of the control voltage signal can expand the dynamic range to near the power supply voltage, and the oscillation frequency can be controlled in that range. Further, since the operating voltage of the oscillation circuit is determined by the voltage of the control voltage signal, the operating voltage is less affected by the fluctuation of the power supply voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment to which a VCO of the present invention is applied.

FIG. 2 is a circuit diagram of a conventional IC VCO.

FIG. 3 is a circuit diagram of another conventional VCO integrated into an IC.

[Explanation of symbols]

 1, 10 VCO, 2, 11 oscillation frequency control circuit, 3 ring oscillator, 4 current mirror circuit, 5, 6, 7 inverter, 8a input terminal, 8b output terminal, 9 PLL loop circuit, 12: Differential amplifier, 13: Next stage amplifier, 14, 15: Constant current source.

Claims (2)

[Claims] 1. An oscillation circuit in which a plurality of inverters connected to a common power receiving line are cascaded in a multistage manner, and an oscillation circuit oscillates by returning an output to an input. A voltage follower that supplies power to the line via an output and controls an oscillation frequency of the oscillation circuit. 2. The semiconductor device according to claim 1, wherein said oscillation circuit is a ring oscillator having a CMOS configuration, and said voltage follower has a differential amplifier circuit having a CMOS configuration and a MOS receiving an output of said differential amplifier circuit.
2. An IC comprising a transistor amplifier, wherein the oscillation circuit and the voltage follower are built in the IC.
A low-voltage driven voltage-controlled oscillator according to any of the preceding claims.