Circuit system adaptively adjusting supply voltage according to temperature and operating method thereof

This application claims the benefit of Taiwan application Ser. No. 103117627, filed May 20, 2014, the subject matter of which is incorporated herein by reference.

The invention relates in general to a circuit system, and more particularly to a technology that adaptively provides a supply voltage in a circuit system.

A voltage-controlled oscillator (VCO) is an essential element commonly applied in various kinds of electronic systems. In general, the temperature of an electronic product rises after a period using the electronic product. The rise in the ambient temperature results a drop in the amplitude of output signals of the VCO, leading to degradation in the phase noise performance. On the other hand, oscillation start-up of a VCO can be more difficult in higher temperatures. For the above issues, in a current solution, the amount of a source current provided to the VCO is adaptively changed according to the ambient temperature. More specifically, the amount of a source current provided to the VCO is increased as the ambient temperature rises, so as to compensate the amplitude of output signals of the VCO.

FIG. 1 shows a schematic diagram of a known technology. An operating power of the VCO 120 is provided by a current source 140 . Generally known to one skilled in the technical field, the current source 140 is a proportional to absolute temperature (PTAT) current source, which outputs an output current I PTAT having a size that is proportional to the absolute temperature. A drawback of the approach in FIG. 1 is that, to minimize the phase noise, a p-type metal-oxide semiconductor field-effect transistor (MOSFET) forming a current mirror in the current source 140 is designed to have a large size, which occupies a considerable chip area.

FIG. 2 shows a schematic diagram of another known technology. An operating power of a VCO 220 is provided by a programmable current source 242 , and a control circuit 244 determines the amount of current to be outputted by the programmable current source 242 according to ambient temperature information detected by a thermal sensor 246 . In practice, the control circuit 244 is usually built-in with a look-up table storing the corresponding relationship between the temperature and the amount of current. One drawback of the approach in FIG. 2 is that the thermal sensor 246 needs to be additionally provided. Another drawback of the approach in FIG. 2 is that, when an internal switch of the programmable current source 242 is switched to adjust the amount of current in response to a looked-up result, a discontinuous change in the source current may lead to jittering in the output frequency of the VCO 220 . For a frequency division duplexing (FDD) system that highly demands a stable connection or a television tuner that requires a stable display image, frequency jittering is a severe issue.

FIG. 3 shows a schematic diagram of yet another known technology. An operating power of a VCO 320 is provided by a programmable current source 342 , and a control circuit 344 determines the amount of current to be outputted by the programmable current source 342 according to ambient temperature information detected by an amplitude detector 346 . With such approach, one drawback is that the amplitude detector 346 needs to be additionally provided, and another drawback is that frequency jittering may also be caused.

As a common feature of the three known technologies above, the amount of a source current is adaptively provided to a VCO according to an ambient temperature. However, the three known technologies also suffer from certain drawbacks.

According to an embodiment of the present invention, a circuit system is provided. The circuit system includes a current supply module, a voltage supply module, and a voltage-controlled oscillator (VCO). The current supply module provides a current adapted to an ambient temperature. The voltage supply module receives the current, and generates an adapted voltage according to the current. The VCO receives the adapted voltage, and generates an oscillation signal according to the adapted voltage. The voltage-controlled oscillator in response to the adapted voltage compensates an amplitude variation of the oscillation signal resulting from a variation of the ambient temperature.

According to another embodiment of the present invention, an operating method for a circuit system is provided. The operating method includes: a) providing a current adapted to an ambient temperature; b) generating an adapted voltage according to the current; and c) generating an oscillation signal according to the adapted voltage. The voltage-controlled oscillator in response to the adapted voltage compensates an amplitude variation of the oscillation signal resulting from a variation of the ambient temperature.

The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.

FIG. 1 to FIG. 3 are schematic diagrams of known temperature compensation technologies;

FIG. 4 is a block diagram of a circuit system according to an embodiment of the present invention;

FIG. 5(A) and FIG. 5(B) are detail diagrams of examples of a current supply module according to an embodiment of the present invention;

FIG. 6(A) and FIG. 6(B) are detail diagrams of examples of a voltage supply module according to an embodiment of the present invention;

FIG. 7(A) to FIG. 7(D) are detail diagrams of examples of a voltage-voltage conversion unit according to an embodiment of the present invention; and

FIG. 8 is a flowchart of an operating method for a circuit system according to an embodiment of the present invention.

It should be noted that, the term “present invention” refers to inventive concepts described by the non-limiting embodiments. Drawings of the present invention include functional block diagrams of multiple functionally associated modules. These drawings are not detailed circuit diagrams, and connection lines therein represent signal flows only. Multiple interactive relationships between the functional elements and/or procedures can be achieved through direct or indirect electrical connections. Further, functions of individual elements need not be assigned as depicted in the drawings, and discrete blocks need not be implemented by discrete electronic elements.

FIG. 4 shows a block diagram of a circuit system according to an embodiment of the present invention. Referring to FIG. 4 , a circuit system 400 includes a current supply module 440 , a voltage supply module 460 and a voltage-controlled oscillator (VCO) 420 . The current supply module 440 provides a current I SUP that changes with an ambient temperature. Therefore, the current is adapted to the ambient temperature. The voltage supply module 460 , coupled to the current supply module 440 , receives the current I SUP and generates an adapted voltage V SUP according to the current I SUP . The VCO 420 , coupled to the voltage supply module 460 , receives the adapted voltage V SUP and generates an oscillation signal according to the adapted voltage V SUP . In the embodiment, the current I SUP generated by the current supply module 440 increases as the temperature rises, and the adapted voltage V SUP generated by the voltage supply module 460 also correspondingly increases as the current I SUP increases. Operation details of the functional blocks are given below.

In the current supply module 440 , a corresponding relationship between the current I SUP and the ambient temperature is designed in a way that the adapted voltage V SUP substantially keeps an amplitude of an output signal of the VCO 420 unaffected from the ambient temperature. In practice, a circuit designer may determine the corresponding relationship between the current I SUP and the ambient temperature for the current supply module 440 according to amplitude characteristics of the VCO 420 . In other words, the corresponding relationship between the current I SUP and the ambient temperature is not limited by the present invention. In one embodiment, the current supply module 440 includes a proportional to absolute temperature (PTAT) current generator for generating a PTAT current as the current I SUP provided to the voltage supply module 460 .

In another embodiment, as shown in FIG. 5(A) , the current supply module 440 includes a PTAT current generator 440 A, a non-temperature related current generator 440 B, and an adder 440 C. The PTAT current generator 440 A generates a PTAT current I PTAT . The non-temperature related current generator 440 B generates a non-temperature related current I BG . The PTAT current I PTAT and the non-temperature related current I BG are added by the adder 440 C to form the current I SUP provided to the voltage supply module 460 . The non-temperature related current I BG generated by the non-temperature related current generator 440 B does not change with the temperature. That is to say, the non-temperature related current I BG stays at a constant value for any temperature, and has an effect of adding a constant current amount to the current I SUP . In practice, whether to add the non-temperature related current I BG to the PTAT current I PTAT is determined according to characteristics of the amplitude of the VCO 420 in response to the temperature. In practice, the non-temperature related current generator 440 B may be implemented by a bandgap current generator.

As shown in FIG. 5(B) , the current supply module 440 may further include a first multiplier 440 D and a second multiplier 440 E. The first multiplier 440 D multiplies the PTAT current I PTAT by a first ratio a to generate a first current component in the current I SUP . The second multiplier 440 E multiplies the non-temperature related current I BG by a second ratio b to generate a second current component in the current I SUP . In practice, the first ratio a and the second ratio b are determined by characteristics of the amplitude of the VCO 420 in response to the temperature. For example, before the circuit system is shipped out of the factory, the characteristics of the amplitude of the VCO 420 in response to the temperature may be obtained through measurement and/or simulation to accordingly appropriately determine the first ratio a and the second ratio b. Further, the first multiplier 440 D and the second multiplier 440 E may be implemented by current mirrors.

As shown in FIG. 6(A) , the voltage supply module 460 may include a current-voltage conversion unit 460 A and a voltage-voltage conversion unit 460 B. The current-voltage conversion unit 460 A converts the current I SUP to an intermediate voltage V INTER . The voltage-voltage conversion unit 460 B converts the intermediate voltage V INTER to the adapted voltage V SUP . For example, the current-voltage conversion unit 460 A may be a resistor element, as shown in FIG. 6(B) . The voltage formed after the current I SUP flows into the resistor is the intermediate voltage V INTER . In practice, the voltage-voltage conversion unit 460 B is a low-dropout (LDO) regulator, a step-down DC-DC converter, a step-up DC-DC converter, or a charge pump. The four possible DC voltage-voltage conversion implementation forms are respectively depicted in FIG. 7(A) to FIG. 7(D) . It should be noted that, details of the current-voltage conversion and voltage-voltage conversion are generally known to one skilled in the technical field, and shall be omitted herein.

It should be noted that, a VCO in many circuit systems is originally provided with a voltage-voltage conversion circuit such as an LDO regulator, whose output voltage does not change with the temperature. In the present invention, by incorporating the current I SUP provided by the current supply module 440 and the current-voltage conversion unit 460 A with the voltage-voltage conversion circuit such as an LDO regulator originally present in the circuit system, the supply source V SUP outputted from the voltage-voltage conversion circuit is caused to change with the temperature to further compensate the amplitude of the oscillation signal of the VCO 420 . That means the voltage-controlled oscillator in response to the adapted voltage compensates an amplitude variation of the oscillation signal resulting from a variation of the ambient temperature. Therefore, the approach based on the present invention does not require numerous additional large-area circuit elements. Further, for a design that adopts a PTAT current generator (e.g., 440 A) or a combination of a PTAT current generator and a bandgap current generator, discontinuous amplitude jittering is not caused when the current I SUP and the adapted voltage V SUP change with the temperature, thereby eliminating the issue of frequency jittering of the known technology.

FIG. 8 shows a flowchart of an operating method for a circuit system according to another embodiment of the present invention. In step S 810 , a current that changes with an ambient temperature is provided. In step S 820 , an adapted voltage is generated according to the current. In step S 830 , an oscillation signal is generated according to the adapted voltage. One person skilled in the technical field can appreciate that, various operations and details disclosed in the description associated with the circuit system 400 are applicable to the operating method for a circuit system in FIG. 8 , and shall be omitted herein.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.