JPH118533A - Voltage-controlled oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of noise due to power source variations by providing 2-phase/1-phase conversion circuits which operate mutually so that power source variations generated by the 2-phase/1-phase conversion circuits cancel each other. SOLUTION: When V1 is applied to an input terminal Vin, a waveform of frequency f(X) is outputted as a differential output from a ring oscillator 101 and inputted to the 2-phase/1-phase conversion circuits 102 and 103. At output terminals OutA and OutB of the 2-phase/1-phase conversion circuits 102 and 103, mutually inverted signals appear, since signals applied to input terminals A and XA of the 2-phase/1-phase converting circuits 102 and 103 are exactly opposite to each other. In this case, variations ΔV generated due to the variations of a source voltage caused by the operation of the 2-phase/1- phase conversion circuits 102 and 103 are equal in quantity and opposite in direction since the 2-phase/1-phase conversion circuits 102 and 103 have symmetrical circuit constitution. Further, the timing also becomes the same. Therefore, the variations ΔV result in canceling each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a voltage controlled oscillation circuit of a PLL used as a clock generator.

[0002]

2. Description of the Related Art In a conventional PLL, a voltage controlled oscillation circuit may be formed using a single-output type ring oscillator having a simple structure. Although a differential output type ring oscillator may be used to obtain a sufficient output amplitude, current consumption increases. Further, when a PLL is used as a clock generator, any method can be adopted, but it is required that the operation of the voltage controlled oscillation circuit does not affect the output waveform.

[0003]

However, in practice, a differential output type ring oscillator is often used to obtain a sufficient output amplitude, and a two-phase / one-phase converter used in combination with the differential output type ring oscillator is often used. Due to the current flowing into and out of the output load during the operation of the circuit, a transient power supply fluctuation occurs on the power supply line, which becomes noise and affects the output signal of the PLL. As a result, this causes jitter in the clock output signal of the PLL.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention solves the above-mentioned problem by using a plurality of two-phase / one-phase converters operating mutually to cancel a power supply fluctuation generated in a two-phase / one-phase conversion circuit. The problem is solved by providing a one-phase conversion circuit.

[0005]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing an embodiment of a voltage controlled oscillation circuit according to the first aspect of the present invention. FIG.
As shown in the figure, two outputs X and XX of the ring oscillator 101 are connected to a two-phase / one-phase conversion circuit 102 and a two-phase / 1-
The input X and the input XA of the phase conversion circuit 103 are respectively connected. FIG. 2 is a diagram showing the internal configuration of the ring oscillator 101. A V / I conversion circuit 201 converts a voltage into a current, and controls a variable current source 202. Also, 20
Reference numeral 3 denotes one type of differential input type operational amplifier, which self-oscillates in a three-stage series connection, and changes the oscillation frequency by changing the power supply current by the variable current source 202. 3 is a diagram showing an internal configuration of the two-phase / one-phase conversion circuit 102, and FIG. 4 is a diagram showing an internal configuration of the two-phase / one-phase conversion circuit 103. The two-phase / one-phase conversion circuit 102 and the two-phase / one-phase conversion circuit 103 have mutually symmetric circuit configurations with respect to VDD or VSS.

FIG. 6 is a diagram showing a configuration of a PLL for a clock generator on which the voltage controlled oscillation circuit of the present invention is mounted. In FIG. 6, reference numeral 601 denotes a quartz oscillator;
Is a crystal oscillation circuit, 603 is a phase comparison circuit, 604 is a low-pass filter, 605 is a voltage controlled oscillation circuit, and 606 is a programmable divider.

Conventionally, as shown in FIG. 7, a differential ring oscillator 101 and a two-phase / one-phase conversion circuit 702 are combined to form a voltage-controlled oscillation circuit. Here, the internal configuration of the two-phase / one-phase conversion circuit 702 is the same as that in FIG. At this time, the voltage Vin at the input terminal Vin and the output frequency f (X) at the output terminal Out have the relationship shown in FIG. For example, the voltage Vin
Is V1, the frequency at the output terminal Out is f (1). FIG. 9 shows the waveform of each part at this time.
9, the waveform A and the waveform XA are those of the input terminals A and XA of the two-phase / one-phase conversion circuit 702 in FIG. 7, the waveform Out is that of the output terminal Out of the two-phase / one-phase conversion circuit 702 in FIG. The waveform IA corresponds to the output terminal Ou in FIG.
It is a waveform of the current flowing through the current source on the tA side. And the waveform V
DD indicates the fluctuation of the power supply voltage of the voltage controlled oscillator.

In the conventional circuit, the fluctuation of the power supply voltage caused by the current IA greatly affects the output characteristics of the PLL, particularly, the jitter. That is, the fluctuation of the power supply voltage due to the operation of the voltage-controlled oscillation circuit becomes noise, which affects other circuits and deteriorates the jitter.

Therefore, the present invention has a circuit configuration as shown in FIG. 1 in order to reduce these effects.

When V1 is applied to the input terminal Vin in the configuration of FIG. 1, a waveform having a frequency of f (X) is output as a differential output from the ring oscillator, and the two-phase / one-phase conversion circuit 1
02 and two-phase / one-phase conversion circuit 103. FIG. 5 shows the waveform of each part at this time. In FIG. 5, waveform X and waveform XX correspond to ring oscillator 1 in FIG.
01, the output terminals X and XX of FIG.
, The waveform OutB of FIG. 1 corresponds to the output terminal OutB of the two-phase / one-phase conversion circuit 103, and the waveform IA corresponds to the output terminal OutA of FIG. IB is a waveform of a current flowing through the current source on the output end OutB side in FIG. The waveform VDDA is the fluctuation of the power supply voltage caused by the operation of the two-phase / one-phase conversion circuit 102, the waveform VDDB is the fluctuation of the power supply voltage generated by the operation of the two-phase / one-phase conversion circuit 103, and the waveform VDD is the VDDA and VDD.
It shows the fluctuation of the power supply voltage of the sum of DB. OutA
And OutB are signals that are opposite to each other since the signals input to the input terminals A and XA of the two-phase / one-phase conversion circuit 102 and the two-phase / one-phase conversion circuit 103 are just opposite. In this case, the change ΔV generated in VDDA and VDDB is also generated in VDDA and VDDB because the two-phase / one-phase conversion circuit 102 and the two-phase / one-phase conversion circuit 103 have a symmetrical circuit configuration with respect to VDD and VSS. Their magnitudes are equal and their directions are opposite to each other. The timing is also the same. Therefore, as a result, the change ΔV is canceled at VDD.

[0012]

As described above, according to the present invention, a plurality of two-phase / one-phase conversion circuits are provided in a voltage-controlled oscillation circuit, and a two-phase / one-phase conversion circuit that cancels out power supply fluctuations generated by each of the two-phase / one-phase conversion circuits. With the configuration described above, the voltage-controlled oscillation circuit does not generate power supply fluctuations, so that noise does not occur, and the PLL having the voltage-controlled oscillation circuit does not affect jitter.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is an internal configuration diagram of a ring oscillator in FIG. 1;

FIG. 3 is an internal configuration diagram of a two-phase / one-phase conversion circuit in FIG. 1;

FIG. 4 is an internal configuration diagram of a two-phase / one-phase conversion circuit in FIG. 1;

FIG. 5 is a diagram for explaining operation waveforms of respective units in FIG. 1;

FIG. 6 shows a PLL in which the voltage controlled oscillation circuit of the present invention is used.
FIG.

FIG. 7 is a configuration diagram showing a conventional voltage controlled oscillation circuit.

FIG. 8 is a diagram showing input / output characteristics of a voltage controlled oscillation circuit.

FIG. 9 is a diagram showing operation waveforms of various parts in a conventional voltage controlled oscillation circuit.

[Explanation of symbols]

 101: Ring oscillator 102: 2-phase / 1-phase conversion circuit 103: 2-phase / 1-phase conversion circuit 201: V / I conversion circuit 202: Variable current source 203: Differential input type operational amplifier 601: Crystal oscillator 602: Crystal oscillation Circuit 603: Phase comparison circuit 604: Low-pass filter 605: Voltage controlled oscillation circuit 606: Programmable divider 702: 2 phase / 1 phase conversion circuit

Claims (1)

[Claims] 1. A voltage controlled oscillation circuit comprising a differential output type ring oscillator and a two-phase / single-phase conversion circuit for converting a differential output of the ring oscillator into an in-phase signal. A voltage-controlled oscillation circuit comprising one or more pairs of the two-phase / one-phase conversion circuit having a symmetrical circuit configuration to suppress power supply fluctuation caused by an oscillation operation.