JPH09275332A - Voltage controlled oscillator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a voltage controlled oscillator circuit in which a variable frequency range is increased without using a frequency divider. SOLUTION: The circuit is provided with plural P-channel control transistors(TRs) 2a-2c whose gate connects to an input circuit via a switch 7 and whose characteristics differ from each other and with plural N-channel control transistors(TRs) 3a-3c whose gate connects to an input circuit via a switch 8 and whose characteristics differ from each other and the frequency variable range is increased depending on the switching of the switches 7, 8.

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 circuit used in a phase locked loop circuit.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional voltage controlled oscillator circuit. In the figure, 1a and 1b are input voltages Vin.
Are p-type and n-type transistors for inputting, and these p-type and n-type transistors 1a and 1b form an input circuit. 2a is a p-type control transistor operated by its input voltage Vin, and 3a is its input voltage V
It is an n-type control transistor operated by in.

4a to 4n are p-type transistors, and 5a to 5n.
n is an n-type transistor, each drain is connected in series, and the series circuit is connected in parallel in an odd number of stages,
The sources of the p-type transistors 4a to 4n are connected to the p-type control transistor 2a, and the sources of the n-type transistors 5a to 5n are connected to the n-type control transistor 3a. Further, the p-type transistor 4a is negatively fed back from the drain having the oscillation frequency Fo of the final stage series circuit to the drain of the first stage series circuit.
4n and n-type transistors 5a to 5n constitute a ring oscillator 6.

Next, the operation will be described. Input voltage Vi
A voltage controlled oscillator circuit that changes the oscillation frequency Fo of an output signal according to a change in n is widely used in a control system including a phase locked loop circuit. In FIG.
Depending on the change of the input voltage Vin, the p-type and n-type of the input circuit
The type transistors 1a and 1b operate, and further the p-type and n-type control transistors 2a and 3a operate. Here, in accordance with the potential difference between the potential Vp of the p-type control transistor 2a on the ring oscillator 6 side and the potential Vn of the n-type control transistor 3a on the ring oscillator 6 side, each of the p-type transistors 4a to 4n and n.
The type transistors 5a to 5n are operated, and the oscillation frequency Fo from the series circuit of the final stage is negatively fed back to the series circuit of the first stage to output the oscillation frequency Fo according to the change of the input voltage Vin. .

By the way, the potentials Vp and Vn are p-type and n-type.
The oscillation frequency Fo increases as the potential difference (Vp-Vn) between the potentials Vp and Vn is determined by the capacitance of the type control transistors 2a and 3a. Therefore, as the input voltage Vin is increased, the ON resistances of the p-type and n-type control transistors 2a and 3a increase, the potential Vp decreases, the potential Vn increases, and the potential difference (Vp-V) increases.
Since n) becomes smaller, the oscillation frequency Fo becomes smaller. FIG. 5 is a characteristic diagram showing oscillation characteristics of this voltage controlled oscillator circuit. When this voltage controlled oscillator circuit is used in a phase locked loop circuit, the lock speed, pull-in range, etc. are taken into consideration due to the characteristics of the phase locked loop circuit. , Input voltage Vi
Since the variable range of n must be limited, there is a limit in increasing the amount of change in the oscillation frequency Fo.

Therefore, in order to generate a wider range of frequency Fck with one voltage controlled oscillator circuit, a plurality of frequency dividers are used as shown in FIG. FIG. 6 is a circuit diagram showing a conventional phase locked loop circuit, in which the input voltage Vin is applied to the voltage controlled oscillator circuit 14 shown in FIG. 4 via the phase comparator 11, the charge pump 12 and the low pass filter 13. The oscillation frequency Fo corresponding to the input voltage Vin is output. Further, the oscillation frequency Fo of the voltage controlled oscillation circuit 14 is 1/2 or 1/3 depending on the selection of the switch 16 by 1/2 and 1/3 frequency dividers 15a and 15b.
The frequency is divided, and the desired frequency division ratio 1 / N is fed back to the phase comparator 11 as the frequency Fck.

FIG. 7 is a characteristic diagram showing the frequency Fck according to the input voltage Vin by the 1/2 and 1/3 frequency dividers 15a and 15b in the phase-locked loop circuit of FIG. The frequency Fc for the input voltage Vin can be changed by switching the frequency division, 1/2 frequency division and no frequency division.
Since k is increased, the frequency variable range can be increased.

[0008]

Since the conventional voltage-controlled oscillator circuit is constructed as described above, when it is used in a phase-locked loop circuit, 1/2 and 1 / in order to increase the frequency variable range. Although the frequency dividers 15a and 15b are used, the frequency divider becomes large in order to keep the duty cycle of the output frequency Fck. That is, the duty cycle can be protected relatively easily with only the 1/2 frequency divider 15a, but the duty cycle can be protected when the 1/3 frequency divider and the 1/5 frequency divider are included. However, there is a problem that a large number of frequency dividers are required and the frequency divider becomes large, and the voltage controlled oscillator circuit becomes large.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a voltage controlled oscillator circuit capable of enlarging the frequency variable range without using a frequency divider.

[0010]

According to a first aspect of the present invention, there is provided a voltage controlled oscillator circuit having a plurality of p-type control transistors each having a different characteristic, each gate being connected to an input circuit through a first switch. And second for each gate
And a plurality of n-type control transistors each having a different characteristic, which are connected to the input circuit via the switch.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1. 1 is a circuit diagram showing a voltage controlled oscillator circuit according to Embodiment 1 of the present invention. In FIG.
Reference characters a and 1b are p-type and n-type transistors for inputting an input voltage Vin, and these p-type and n-type transistors 1a and 1b form an input circuit. 2a to 2c operate according to their input voltage Vin, p-type control transistors having different characteristics, and 3a to 3c operate according to their input voltage Vin, and have different characteristics.
Type control transistor.

4a to 4n are p-type transistors, and 5a to 5n.
n is an n-type transistor, each drain is connected in series, and the series circuit is connected in parallel in an odd number of stages,
The sources of the p-type transistors 4a to 4n are connected to the p-type control transistors 2a to 2c, and the sources of the n-type transistors 5a to 5n are connected to the n-type control transistors 3a to 3c. Further, the drain that is the oscillation frequency Fo of the series circuit of the final stage is negatively fed back to the drain of the series circuit of the first stage, and these p-type transistors 4a to 4n and n-type transistors 5a to 5n are used.
The ring oscillator 6 is constituted by Further, 7 is a switch (first switch) connected between the gate of each of the p-type control transistors 2a to 2c and the input circuit, and 8 is each of the n-type control transistors 3a to 3c.
Is a switch (second switch) connected between the gate and the input circuit.

Next, the operation will be described. In FIG. 1, p-type and n-type transistors 1a and 1b of the input circuit operate according to changes in the input voltage Vin, and further p-type and n-type control transistors 2a to 2c depending on the selection of the switches 7 and 8. 3a to 3c operate. Here, according to the potential difference between the potential Vp of the p-type control transistors 2a to 2c on the ring oscillator 6 side and the potential Vn of the n-type control transistors 3a to 3c on the ring oscillator 6 side, each of the p-type transistors 4a to 4n and n. The type transistors 5a to 5n are operated, and the oscillation frequency Fo from the series circuit of the final stage is negatively fed back to the series circuit of the first stage to output the oscillation frequency Fo according to the change of the input voltage Vin. .

By the way, the potentials Vp and Vn are p-type and n-type.
Determined by the capacitance of the type control transistors 2a to 2c and 3a to 3c, the potential difference (Vp between potentials Vp and Vn
The oscillation frequency Fo increases as −Vn) increases. Therefore, as the input voltage Vin is increased, p-type and n-type
The on-resistances of the type control transistors 2a and 3a increase, the potential Vp decreases, the potential Vn increases, and the potential difference (Vp-Vn) decreases, so the oscillation frequency Fo decreases.

As described above, the potentials Vp and Vn that determine the oscillation frequency Fo are the input voltage Vin and the capacitances of the p-type and n-type control transistors 2a to 2c and 3a to 3c.
That is, since it is determined by the characteristics, the p-type and n-type control transistors 2a to 2 having different characteristics.
By selecting c, 3a to 3c by the switches 7 and 8, the potentials Vp and Vn can be changed even with the same input voltage Vin, and a combination of the p-type and n-type control transistors 2a to 2c and 3a to 3c. An oscillation frequency Fo of several minutes can be obtained.

FIG. 2 is a circuit diagram showing a phase locked loop circuit using this voltage controlled oscillator circuit.
Through the charge pump 12 and the low pass filter 13,
The voltage control oscillator circuit 17 shown in FIG.
n is input, and the oscillation frequency Fo corresponding to the input voltage Vin is output. Here, as shown in FIG. 3, the switches 7 and 8 are switched so as to obtain a desired oscillation frequency Fo, and, for example, p-type and n-type control transistors (2a, 3a), (2b, 3b), ( 2c, 3c), the variable range of the frequency is switched, and the variable range of the oscillation frequency Fo can be increased. Therefore, the desired frequency Fck can be fed back to the phase comparator 11 without using a frequency divider as in the conventional case.

As described above, according to the first embodiment, the p-type and n-type control transistors 2a to 2c and 3a having different characteristics are used without using a frequency divider.
Since the frequency variable range of the oscillation frequency Fo can be increased by the combination of 3c,
The circuit can be simplified and the layout area can be reduced without using a complicated and large circuit such as a frequency divider. Further, even when changing the frequency variable range, it is sufficient to connect the p-type and n-type control transistors 2a to 2c and 3a to 3c having different characteristics via the switches 7 and 8, which is an extremely easy effect. .

[0018]

As described above, according to the first aspect of the present invention, a plurality of p-type control transistors each having different characteristics are connected to the input circuit for each gate through the first switch, and each p-type control transistor has a different characteristic. Since each gate is provided with a plurality of n-type control transistors which are connected to the input circuit through the second switch and have different characteristics, without using a complicated and large circuit such as a frequency divider. The circuit can be simplified and the layout area can be reduced. Further, even in the case of changing the frequency variable range, since it is only necessary to connect the p-type and n-type control transistors having different characteristics via the first or second switch, it is possible to achieve an extremely easy effect.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a phase locked loop circuit using the voltage controlled oscillator circuit according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing an oscillation frequency according to an input voltage by switching a switch of the voltage controlled oscillator circuit according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional voltage controlled oscillator circuit.

FIG. 5 is a characteristic diagram showing oscillation characteristics in a conventional voltage controlled oscillation circuit.

FIG. 6 is a circuit diagram showing a conventional phase locked loop circuit.

7 is a characteristic diagram showing a frequency according to an input voltage by the 1/2 and 1/3 frequency dividers in the phase locked loop circuit of FIG.

[Explanation of symbols]

1a p-type transistor (input circuit), 1b n-type transistor (input circuit), 2a to 2c p-type control transistor, 3a to 3c n-type control transistor, 7 switch (first switch), 8 switch (second switch) ) 4a-4n p-type transistors,
5a to 5n n-type transistor, 6 ring oscillator, 17 voltage controlled oscillator circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H03L 7/187 H03L 7/18 D

Claims (1)

[Claims] 1. A plurality of p-type control transistors each of which is connected to an input circuit via a first switch for each gate and has different characteristics, and each gate is connected to the input circuit via a second switch. A plurality of n-type control transistors each having different characteristics, and drains of the p-type transistor and the n-type transistor are connected in series, and the series circuit is connected in parallel in an odd number of stages.
A voltage controlled oscillation circuit comprising: a ring oscillator in which the sources of the p-type transistors are connected to the p-type control transistors and the sources of the n-type transistors are connected to the n-type control transistors.