CN112953396B

CN112953396B - Variable-capacitance voltage-controlled oscillator and integrated circuit

Info

Publication number: CN112953396B
Application number: CN202110371282.6A
Authority: CN
Inventors: 吴洁; 姜自力; 林烨; 裔鹏; 谢芳; 姜德伟; 马怀昌
Original assignee: Shanghai Ruixing Microelectronics Technology Co ltd
Current assignee: Shanghai Ruixing Microelectronics Technology Co ltd
Priority date: 2021-04-07
Filing date: 2021-04-07
Publication date: 2022-03-22
Anticipated expiration: 2041-04-07
Also published as: CN112953396A

Abstract

A voltage-controlled oscillator comprises a crystal, wherein one end X1 of the crystal is connected with one end of a first MOS varactor; the other end X2 of the crystal is connected with one end of a second MOS varactor; the other end of the first MOS varactor and the other end of the second MOS varactor are connected in series to a contact A; the contact A is connected with a power supply end of the voltage-controlled oscillator. The contact A is connected with a power supply end of the voltage-controlled oscillator through a third resistor.

Description

Variable-capacitance voltage-controlled oscillator and integrated circuit

Technical Field

The invention belongs to the technical field of electronic circuits, and particularly relates to a variable-capacitance voltage-controlled oscillator and an integrated circuit.

Background

With the rapid development of microelectronics, many digital circuits need to rely on precise clocks to accurately sequence various states and data processes. Quartz crystal oscillators are often required for these systems, and VCXOs (voltage controlled oscillators) are becoming an important application for increasingly sophisticated requirements.

Disclosure of Invention

In an embodiment of the present invention, a voltage controlled oscillator includes a crystal, an amplifier connected in parallel between two ends of the crystal, and a first resistor. One end X1 of the crystal is connected with one end of a first MOS varactor; the other end X2 of the crystal is connected with one end of a second MOS varactor; the other end of the first MOS varactor and the other end of the second MOS varactor are connected in series to a contact A; the contact A is connected with a power supply end of the voltage-controlled oscillator. The contact A is connected with a power supply end of the voltage-controlled oscillator through a third resistor.

Preferably, the voltage-controlled oscillator includes a plurality of MOS varactors, the MOS varactors are connected in series two by two, the connection points of the series connection of the MOS varactors are respectively connected to a voltage conversion configuration circuit, and the input of the voltage conversion configuration circuit is connected to the power supply terminal of the voltage-controlled oscillator through a third resistor.

One of the benefits of the embodiment of the invention is that a novel non-blocking oscillator framework and a novel multi-stage variable capacitor module are adopted, so that the capacitance rate and the wider capacitance-pull rate (pull-range) required by the voltage-controlled oscillator are met, and the cost is reduced. The capacitance pull rate refers to the change in the capacitance change rate of the capacitance as the voltage changes.

Drawings

The above and other objects, features and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:

fig. 1 is a schematic diagram of a prior art voltage controlled oscillator VCXO circuit.

Fig. 2 is a schematic diagram of a vco according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of a vco according to an embodiment of the present invention.

Fig. 4 is a graph of simulated capacitance pull rate of a vco circuit according to an embodiment of the invention.

Fig. 5 is a schematic diagram of a voltage conversion configuration circuit according to an embodiment of the invention.

1-crystal oscillator (crystal), 2-first resistor, 3-amplifier, 8-third resistor, 10-first MOS varactor, 11-second MOS varactor, 13-voltage conversion configuration circuit, 101-first and second MOS varactor, 111-second MOS varactor.

Detailed Description

In the conventional VCXO circuit, a blocking capacitor is used between the varactor diode and both ends X1/X2 of the external crystal, and several tens of PF is required. Due to the series connection of the blocking capacitor (fixed capacitor), the lower varactor needs to have a larger capacitance change rate, so that the same load capacitance change rate of the crystal can be met. Taking a chip with a load capacitance variation range of 3.2 times as an example, the capacitance variation range of the varactor needs to be more than 6 times due to the existence of the blocking capacitor. Meanwhile, due to the existence of parasitic capacitance with relatively fixed capacitance value, the capacitance change rate of the variable diode is generally required to be 8-10 times. The area of the capacitor greatly affects the cost of the product.

Fig. 1 shows a schematic diagram of a conventional VCXO with a dc blocking capacitor. Cpg and Cpd are blocking capacitors, and the varactor of this architecture is grounded.

In accordance with one or more embodiments, as shown in fig. 2, a non-blocking capacitively coupled voltage controlled oscillator eliminates the need for blocking capacitors Cpg/Cpd due to the use of MOS varactors, 2 of which are connected to the voltage VC via a resistor after connection at node a. The MOS varactor is formed by connecting the source electrode, the drain electrode and the substrate of an MOSFET standard tube or a slightly improved MOS tube, so that the MOS varactor becomes a two-end device; the capacitance utilized is the capacitance between the gate and the source. The size of the capacitor is controlled by the voltage VGB between the gate and the substrate. The same frequency pulling range has lower requirement on the capacitance variation rate of the MOS varactor. The total rate of change of capacitance of the variable capacitance is around 3.5. Both forward and reverse biases can cause their capacitance to vary, but the capacitance variation occurs most predominantly within +/-0.7v of the bias. Since the capacitance variation of the MOS varactor only occurs between +/-0.7 v. The variation of the input control voltage 0v to 3.3v needs to be mapped to the +/-0.7v bias voltage according to the frequency versus load capacitance variation curve. Therefore, a conversion circuit for inputting a control voltage is needed, and the MOS varactor is subdivided into an array for optimal configuration and multistage adjustment to obtain good linearity.

According to one or more embodiments, as shown in fig. 3, a schematic diagram of a multi-stage linear tunable variable capacitance voltage-controlled oscillator may finally obtain a capacitance pulling rate of ± 200ppm and good linearity by configuring different VC voltages corresponding to different MOS varactor array sizes.

In the embodiment of the invention, three-level adjustability is used, the capacitance value of the variable capacitor is redistributed in the whole range that VC is equal to 0-3.3V, and the linearity of the capacitance traction rate of each section is adjusted by adjusting the capacitance values under different control voltages, so that the capacitance traction rate is adjusted to the maximum range of +/-200 ppm and has good linearity.

Fig. 4 is a schematic diagram of the capacitance traction ratio of the circuit according to the embodiment of the present invention, which shows that the present invention does not use a large-area dc blocking capacitor, and reduces the cost. And the VC voltage value is redistributed through a VC voltage conversion configuration circuit, so that the voltage-controlled oscillator with multi-stage linear adjustment is realized, as shown in figure 5.

The invention uses a non-blocking capacitor coupling oscillator framework, does not use a large-area blocking capacitor, overcomes the difficult problem of the blocking capacitor, and reduces the cost. Meanwhile, a multi-stage adjustable variable capacitor is adopted, so that the capacitance traction rate (pull _ range) required by design and good linearity are achieved.

It should be noted that while the foregoing has described the spirit and principles of the invention with reference to several specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, nor is the division of aspects, which is for convenience only as the features in these aspects cannot be combined. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A voltage-controlled oscillator comprises a crystal and is characterized by comprising a plurality of MOS varactors which are connected in series two by two, wherein,

one end X1 of the crystal is connected with one end of a first MOS varactor;

the other end X2 of the crystal is connected with one end of a second MOS varactor;

the other end of the first MOS varactor and the other end of the second MOS varactor are connected in series to a contact A;

the contact A is connected with a power supply terminal of the voltage-controlled oscillator through a third resistor,

an amplifier is connected in parallel between the two ends of the crystal,

a first resistor is connected in parallel between two ends of the crystal,

the source electrode and the drain electrode of the first MOS varactor are connected with the substrate, the source electrode and the drain electrode of the second MOS varactor are connected with the substrate, the capacitance of the first MOS varactor and the capacitance of the second MOS varactor are the capacitance between the grid electrode and the source electrode, the capacitance is controlled by a bias voltage VGB between the grid electrode and the substrate, the bias range of the bias voltage VGB is +/-0.7v,

the contact A is connected with a voltage conversion configuration circuit, the series connection contacts of other MOS varactor pairs are also connected with the voltage conversion configuration circuit,

and the input of the voltage conversion configuration circuit is connected with a power supply end of the voltage-controlled oscillator through a third resistor.

2. A voltage controlled oscillator integrated circuit, comprising a plurality of MOS varactors, the MOS varactors being connected in series, wherein,

a first MOS varactor and a second MOS varactor,

one end of the first MOS varactor and one end of the second MOS varactor are connected in series at a contact point A,

the contact A is connected with a power supply terminal of the voltage-controlled oscillator integrated circuit through a third resistor,

the other end node of the first MOS varactor is X1,

the other end node of the second MOS varactor is X2,

an amplifier and a first resistor are connected in parallel to nodes X1 and X2,

the source electrode and the drain electrode of the first MOS varactor are connected, the source electrode and the drain electrode of the second MOS varactor are connected, the capacitance of the first MOS varactor and the capacitance of the second MOS varactor are the capacitance between the grid electrode and the source electrode,

the contact A is connected with a voltage conversion configuration circuit, other series-connected contacts are also respectively connected with the voltage conversion configuration circuit,

and the input of the voltage conversion configuration circuit is connected with a power supply end of the voltage-controlled oscillator integrated circuit through a third resistor.

3. An electronic device comprising the voltage controlled oscillator integrated circuit of claim 2 and a crystal.