JPH09321582A - Ring oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ring oscillator oscillating a polyphase high frequency signal in which waveform distortion is less, frequency stability is high, and a phase error is hardly caused. SOLUTION: Three stages or over of positive feedback differential amplifier circuits 4A each of which a capacitor 5 is connected between a noninverting input terminal 4a and a noninverting output terminal 4b and between an inverting input terminal 4c and an inverting output terminal 4d of a 2-input 2-output differential amplifier circuit 4 are connected in series, and the noninverting input terminal 4a of the 1st stage is connected to the inverting output terminal 4d of the final stage and the inverting input terminal 4c of the 1st stage is connected to the noninverting output terminal 4b of the final stage. Furthermore, a resistor is inserted between the noninverting output terminal 4b and the capacitor 5 and between the inverting output terminal 4d and the capacitor 5 respectively in each differential amplifier circuit 4. Variable resistors are adopted for the resistors above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring oscillator used in digital communication terminals and the like.

[0002]

2. Description of the Related Art An oscillation circuit is one of important element circuits in electronic circuits. In particular, in digital communication terminals such as digital cellular and PHS, a phase modulation method is used, and a high frequency, high phase accuracy polyphase oscillator is required. In recent years, in these digital communication terminals, there are great demands for size reduction, weight reduction, voltage reduction, and cost reduction, and monolithic communication circuits including an oscillation circuit are desired.

Conventionally, the capacitor 8 as shown in FIG.
An LC oscillator including an inductor 9 and the like and a frequency divider 10 are provided, and the output of the oscillator is frequency-divided to obtain signals having different phases. Since the LC oscillator is used, the frequency stability is high, but the output signal of the oscillator is divided by the frequency divider 10 to obtain a polyphase signal, which is disadvantageous in obtaining a high-frequency polyphase signal. Further, in a semiconductor integrated circuit, it is difficult to incorporate a high-quality inductor, which is also disadvantageous in making a communication circuit monolithic.

The ring type oscillator is an oscillator which is effective for monolithic because it can easily obtain a high-frequency multiphase signal and can be realized without using an inductor element. FIG. 7 shows an example of a conventional ring oscillator. As shown in the figure, the differential amplifier 1
A circuit composed of 1, a resistor 12, and a capacitor 13 is connected in a ring shape to oscillate. The oscillation frequency of this oscillator is usually determined by the cutoff frequency by the capacitor 12 and the resistor 13.

[0005]

However, in such a ring type oscillator, the capacitor 12 and the resistor 1 are used.
Since 3 is an integrating circuit, when a DC component occurs in the signal path, the potential is amplified and stored in the capacitor 12 at the next stage. The accumulated potential is amplified one after another and accumulated in the capacitor 12 of the next stage, so that the potential of the signal rises to the saturation region of the amplifier. In this region, the oscillation frequency is no longer determined by the cutoff frequency by the capacitor 12 and the resistor 13, the output waveform is greatly distorted, and the frequency stability is low. In particular, at high frequencies, the output impedance of the differential amplifier 11 changes depending on the output potential of the signal, so a DC component is likely to occur. FIG. 8 shows a simulation result of the conventional ring oscillator shown in FIG. The total harmonic distortion rate of this output waveform is 7.1%, and it can be seen that there is a difference between the rising time and the falling time of the waveform. When operating the circuit in the high frequency band, the operating point of the circuit changes depending on the rise time or fall time. Due to the difference between the rise time and the fall time, a phase error is likely to occur in the conventional ring oscillator, which makes it difficult to apply the circuit to a circuit such as a wireless terminal that requires high phase accuracy.

The present invention has been made in order to solve the above-mentioned problems, and has less waveform distortion and high frequency stability.
An object of the present invention is to provide a ring-type oscillator that oscillates a multiphase high frequency in which a phase error is unlikely to occur.

[0007]

In order to achieve this object, in the present invention, five or more positive feedback amplifier circuits in which a capacitor is connected between the input terminal and the output terminal of the non-inverting amplifier circuit are connected in series. The input terminal of the positive feedback amplifier circuit of the first stage and the output terminal of the final stage are connected.

A resistor is inserted between the output terminal of the non-inverting amplifier circuit and the connection point of the capacitor.

Further, three or more stages of positive feedback differential amplifier circuits in which capacitors are connected between the positive input terminal and the positive output terminal and between the negative input terminal and the negative output terminal of a two-input two-output differential amplifier circuit are connected in series. , Connecting between the positive input terminal of the positive feedback differential amplifier circuit of the first stage and the negative output terminal of the final stage, and further connecting between the negative input terminal of the first stage and the positive output terminal of the final stage. Connecting.

Resistors are respectively inserted between the positive output terminal and the negative output terminal of the differential amplifier circuit and the connection point of the capacitor.

Further, the resistance is variable.

Further, the capacitor is variable.

[0013]

1 is a block diagram showing an embodiment of a ring oscillator according to the present invention. As shown in the figure, a capacitor 2 is connected between the input terminal 1a and the output terminal 1b of the non-inverting amplifier circuit 1 having an amplification degree A, and a resistor 3 is connected between the output terminal 1b and the capacitor 2 as required. The positive feedback amplifier circuit 1A connected between the point 2a and the positive feedback amplifier circuit 1A is connected in series in five or more stages, and the input terminal 1a of the first stage (first stage) is further connected.
And the output terminal 1b of the final stage (nth stage) are connected via a resistor 3 as required. This ring oscillator has an oscillation frequency f = tanτ / 4π (1-cosτ) RC, τ
= 2π / n and the amplification degree A of the non-inverting amplifier circuit 1 is A
= √ (1 + tan ² τ), the amplification of the ring oscillator is 1
Becomes stable. In this ring oscillator, the phase does not delay by 90 degrees or more per stage of the non-inverting amplifier circuit 1, so the non-inverting amplifier circuit 1 needs to be composed of five stages or more.

Further, in this ring type oscillator, when a DC component is generated in the signal path, the capacitor operates as a bypass filter for this DC component, so that the DC component is not accumulated and non-inverting amplification is performed. Waveform distortion due to saturation of the circuit 1 does not occur. Further, the current flowing in the capacitor 2 is not only supplied from the non-inverting amplifier circuit 1, but also the capacitors 2 connected to each other exchange the current in synchronization with the oscillation signal. For this reason, even if noise occurs in the non-inverting amplifier circuit 1, it has a function of absorbing the noise, so that the oscillation stability is higher than that of the conventional ring oscillator.

Further, when the present ring type oscillator is configured by four or more even-numbered stages, the phases between the output signals of the non-inverting amplifier circuit 1 which are n / 2 apart are 180 degrees out of phase, so these are combined into one. It can be composed of a differential amplifier. Therefore, a ring-type oscillator can be configured with three or more stages of differential amplifiers.

FIG. 2 is a configuration diagram showing another embodiment of the ring oscillator according to the present invention. As shown in FIG. 2A, a positive feedback difference in which a capacitor 5 is connected between the positive input terminal 4a and the positive output terminal 4b of the 2-input 2-output differential amplifier circuit 4 and between the negative input terminal 4c and the negative output terminal 4d. The dynamic amplification circuit 4A is connected in series in three or more stages, and the positive input terminal 4a of the first stage is connected.
And the negative output terminal 4d of the final stage are connected, and further, the negative input terminal 4c of the first stage and the positive output terminal 4b of the final stage are connected. The differential amplifier circuit 4 is composed of a circuit including a bipolar transistor as shown in FIG. The amplification degree of the differential amplifier circuit 4 is resistance R1, R2, R
Determined by 3 and R4. In the circuit of FIG. 2B, oscillation occurs when the amplification factor is √2 or more. If the amplification degree is larger than √2, the amplitude of the oscillation signal increases, but the amplification degree decreases in the differential amplifier circuit 4 when the input signal level increases, so the oscillation stabilizes when the amplification degree becomes √2. To do.
Further, since the output impedance of the differential amplifier circuit 4 changes depending on the currents flowing through the transistors Q6 and Q7, the frequency can be changed by changing the current value.

Further, resistors are respectively inserted between the positive output terminal 4b and the negative output terminal 4d of the differential amplifier circuit 4 and the connection point of the capacitor 5, and the resistors are made variable, whereby the oscillation frequency is changed. Can be changed. Changing the output impedance of the circuit of FIG. 2 (b) is equivalent to changing the resistance.

3 and 4 show simulation execution results of the ring oscillator shown in FIG. FIG. 3 is a rising waveform of oscillation. It can be seen that when the power is turned on at the time of 2nSec, the oscillation amplitude is amplified and the oscillation is stable at 8nSec. Further, the total harmonic distortion rate of the output waveform was 0.8%, which was a waveform very close to a sine wave. Further, FIG. 4 shows the relationship between the current values of the transistors Q6 and Q7 and the oscillation frequency. As shown in the figure, from 1.0 GHz
It can be seen that the frequency is variable in a wide range of 2.4 GHz.

FIG. 5 is a configuration diagram showing still another embodiment of the ring oscillator according to the present invention. FIG.
As shown in (b), the differential amplifier 6 is composed of CMOS transistors and the like. As shown in the figure, the oscillation frequency can be adjusted by the variable resistor composed of the transistors Q4 and Q5. In the circuit of FIG. 2B, the circuit current is large because the frequency control is performed by the bias current. However, in the circuit of FIG. 5B, the frequency control is performed by the variable resistance of the CMOS transistor, so that the circuit current is low. There is an effect that it is advantageous for power conversion.

In the above-described embodiment, the example in which the frequency control is performed by the variable resistor has been shown, but it goes without saying that the frequency control can be similarly performed by making the capacitor variable.

[0021]

As described above, in the ring oscillator according to the present invention, even when the positive feedback amplifier circuits are connected in series of 5 or more stages, the positive feedback differential amplifier circuits are connected in series of 3 stages or more. Also in the case, it is possible to realize a ring-type oscillator that oscillates a multi-phase high frequency in which the waveform distortion is small, the frequency stability is high, and the phase error hardly occurs.

The oscillation frequency can be made variable by inserting a resistor in the positive feedback amplifier circuit or the positive feedback differential amplifier circuit and making the resistor variable.
The oscillation frequency can also be made variable by making the capacitor variable.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a ring oscillator according to the present invention.

FIG. 2 is a configuration diagram (configuration example of a bipolar transistor or the like) showing another embodiment of a ring oscillator according to the present invention.

FIG. 3 is a simulation execution result (startup waveform) of the ring oscillator shown in FIG.

FIG. 4 is a simulation execution result (frequency variable characteristic) of the ring oscillator shown in FIG.

FIG. 5 is a configuration diagram (configuration example using CMOS transistors) showing yet another embodiment of a ring oscillator according to the present invention.

FIG. 6 is an example of a prior art oscillator using an LC oscillator.

FIG. 7 is an example of a conventional ring oscillator.

FIG. 8 is a simulation execution result of a conventional ring oscillator.

[Description of symbols] 1A Positive feedback amplifier circuit 1 Non-inverting amplifier circuit 1a Input terminal 1b Output terminal 2 Capacitor 2a Connection point 3 Resistor 4A Positive feedback differential amplifier circuit 4 Differential amplifier circuit 4a Input terminal 4b Output terminal 4c Input terminal 4d Output terminal 5 Capacitor 6 Differential amplifier circuit

Claims (6)

[Claims] 1. A positive feedback amplifier circuit in which a capacitor is connected between an input terminal and an output terminal of a non-inverting amplifier circuit is connected in series in five or more stages, and the input terminal and the final stage of the positive feedback amplifier circuit in the first stage are connected. A ring-type oscillator having a configuration in which the output terminal is connected. 2. The ring oscillator according to claim 1, wherein a resistor is inserted between the output terminal of the non-inverting amplifier circuit and the connection point of the capacitor. 3. A positive feedback differential amplifier circuit in which a capacitor is connected between the positive input terminal and the positive output terminal and the negative input terminal and the negative output terminal of a 2-input 2-output differential amplifier circuit is connected in series in three or more stages. , Connecting between the positive input terminal of the positive feedback differential amplifier circuit of the first stage and the negative output terminal of the final stage, and further connecting between the negative input terminal of the first stage and the positive output terminal of the final stage. A ring oscillator characterized by having a connected configuration. 4. Between the positive output terminal and the negative output terminal of the differential amplifier circuit and the connection point of the capacitor,
4. The ring type oscillator according to claim 3, wherein resistors are respectively inserted. 5. The ring oscillator according to claim 2 or 4, wherein the resistance is variable. 6. The ring oscillator according to claim 1, wherein the capacitor is variable.