Method and apparatus for starting up oscillation

This present disclosure claims the benefit of U.S. Provisional Application No. 61/557,279, “XTAL Noise Injection to Speed Up Start Up” filed on Nov. 8, 2011, which is incorporated herein by reference in its entirety.

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Generally, when power is first applied to a system, it takes a time period for a crystal oscillator to build up a magnitude of an oscillation signal to a relatively stable level. Based on the stabled oscillation signal, a system clock is generated. Then, the system clock is distributed in the system, and used by various circuits in the system.

Aspects of the disclosure provide a circuit. The circuit includes a signal amplifying circuit coupled with a crystal component of a natural frequency to form a crystal oscillator, and a signal generator circuit configured to generate a signal with an energy distribution about the natural frequency, and to provide the signal to the crystal oscillator to assist the crystal oscillator to begin oscillating.

Further, the circuit includes an interface circuit configured to couple the signal to the signal amplifying circuit when the circuit is powered up. In an example, the interface circuit is configured to decouple the signal from the signal amplifying circuit after a time duration.

According to an aspect of the disclosure, the signal generator circuit is configured to generate the signal with energy distributed in a frequency range about the natural frequency. In an embodiment, the signal generator circuit includes a ring oscillator configured to generate an oscillation signal with a frequency varying in the frequency range. In an example, the signal generator circuit includes a plurality of switchable capacitors configured to vary a capacitance load of the ring oscillator. For example, the signal generator circuit includes a control signal generator configured to generate control signals to control the plurality of switchable capacitors.

Aspects of the disclosure provide a method. The method includes generating a signal with an energy distribution in a frequency range about a natural frequency of a crystal component, and providing the signal to a crystal oscillator formed by the crystal component to assist the crystal oscillator to begin oscillating.

Aspects of the disclosure provide a system. The system includes a crystal component configured to have a natural frequency, a signal amplifying circuit coupled with the crystal component to form a crystal oscillator, and a signal generator circuit configured to generate a signal with an energy distribution about the natural frequency, and to provide the signal to the crystal oscillator to assist the crystal oscillator to begin oscillating.

Various embodiments of this disclosure that are proposed as examples will be described in detail with reference to the following figures, wherein like numerals reference like elements, and wherein:

FIG. 1 shows a diagram of an electronic system example 100 according to an embodiment of the disclosure;

FIG. 2 shows a diagram of a noise generator example according to an embodiment of the disclosure;

FIG. 3 shows a plot of a power spectrum example 300 according to an embodiment of the disclosure;

FIG. 4 shows a diagram of a noise generation control circuit example 480 according to an embodiment of the disclosure; and

FIG. 5 shows a flowchart outlining a process example according to an embodiment of the disclosure,

FIG. 1 shows a diagram of an electronic system example 100 according to an embodiment of the disclosure. The electronic system 100 includes a crystal oscillator 110 to provide an oscillation signal for generating a system clock in the electronic system 100 . In addition, the electronic system 100 includes a noise generator 150 configured to provide a noise signal to the crystal oscillator 110 to assist the crystal oscillator 100 to start oscillation, and to achieve a stable level of amplitude in a relatively short time.

In the FIG. 1 example, the crystal oscillator 110 includes a crystal component 111 , a gain stage 130 , and capacitors C 1 and C 2 . These elements are coupled together as shown in FIG. 1 . The crystal component 111 , such as a quartz crystal, has a natural frequency f T that is substantially fixed for the crystal component 111 . The crystal component 111 behaves like a filter to allow a signal portion that has the natural frequency f T (an oscillation signal of the natural frequency f T ) to pass through, and to attenuate other signal portions.

The gain stage 130 includes any suitably circuits to amplify signals received at its input. The capacitors C 1 and C 2 are used to stabilize the operation of the crystal oscillator 110 .

In operation, when power is first applied to the crystal oscillator 110 , the gain stage 130 amplifies signals received at its input, such as the noise signal provided by the noise generator 150 , thermal noise, and the like. The crystal component 111 filters the amplified signals to let the signal portion that has the natural frequency f T to pass through, and generate the oscillation signal of the natural frequency f T . The gain stage 130 then further amplifies the oscillation signal and other signals received at its input. This process continues until the oscillation signal reaches a relatively stable level, which is typically governed by a power supply voltage level of the gain stage 130 . The time duration from the power being applied to the oscillation signal being stable is referred to as a start-up time for oscillation.

According to an embodiment of the disclosure, at the time when the power is first applied, the noise generator 150 intentionally generates and provides the noise signal to the crystal oscillator 110 . The noise signal has energy distribution on the natural frequency f T . In an example, the energy distribution of the noise signal on the natural frequency f T is much larger than thermal noise in the circuit. Thus, based on the noise signal, the crystal oscillator 110 takes less time to achieve the stable amplitude of oscillation, and has a reduced start-up time for oscillation compared to thermal noise based start-up time for oscillation.

Specifically, in an embodiment, the gain stage 130 and the noise generator 150 are implemented on an integrated circuit (IC) chip 120 in the electronic system 100 . Further, the IC chip 120 includes a noise injection interface 140 configured to couple/decouple the noise generator 150 to the crystal oscillator 110 .

In the FIG. 1 example, the noise generator 150 is configured to generate a noise signal OUT NOISE when power is applied to the IC chip 120 , for example. The noise signal OUT NOISE has a larger energy distribution at the natural frequency f T than thermal noise in the circuit. The noise injection interface 140 is configured to couple the noise signal OUT NOISE to the input of the gain stage 130 when the power is first applied to the IC chip 120 .

Further, according to an embodiment of the disclosure, the noise injection interface 140 decouples the noise signal OUT NOISE from the crystal oscillator 110 after a suitable time, such as after a pre-determined time period, when the oscillation signal is stable, and the like.

In an example, the noise injection interface 140 includes a capacitor C N for noise coupling, a T switch formed by switches TS 1 -TS 3 , and a noise injection control circuit 141 . The noise injection control circuit 141 provides control signals to the switches TS 1 -TS 3 . It is noted that the switches TS 1 -TS 3 can be implemented using any suitable techniques, such as using metal-oxide-semiconductor (MOS) transistors.

During operation, in an example, when power is first applied to the IC chip 120 , the noise injection control circuit 141 provides control signals to the switches TS 1 -TS 3 to close the switches TS 1 and TS 2 , and open the switch TS 3 , such that the noise generator 150 is AC-coupled to the input of the gain stage 130 , and thus the input of the gain stage 130 receives the noise signal generated by the noise generator 150 .

Then, after a suitable time duration, the noise injection control circuit 141 adjusts the control signals to the switches TS 1 -TS 3 to close the switches TS 1 and TS 3 and open the switch TS 2 , such that the noise generator 150 is decoupled from the input of the gain stage 130 .

It is noted that, in another embodiment, after a suitable time duration, the noise generator 150 is disabled, and thus stops providing the noise signal OUT NOISE to the crystal oscillator 110 .

According to an aspect of the disclosure, the electronic system 100 generates a system clock based on the stable oscillation signal, and distributes the system clock to circuits in the electronic system 100 . For example, the IC chip 120 includes a clock generator 121 configured to generate one or more clock signals based on the oscillation signal. For example, the clock generator 121 generates a first clock signal CLOCK_ 1 , and provides the first clock signal CLOCK_ 1 to functional circuits 122 on the IC chip 120 . In addition, the clock generator 121 generates a second clock signal CLOCK_ 2 and provides the second clock signal CLOCK_ 2 to components out of the IC chip 120 , such as other IC chips 101 , and the like.

It is noted that the electronic system 100 can be suitably modified. For example, the noise generator 150 is out of the IC chip 120 in an embodiment. Further, in an example, the noise generator 150 is powered up at the same time as the IC chip 120 or before the IC chip 120 .

The noise generator 150 can be implemented by various techniques.

FIG. 2 shows a diagram of a noise generator example 250 according to an embodiment of the disclosure. The noise generator 250 includes a ring oscillator 260 , a switchable capacitor bank 270 and a noise generation control circuit 280 . These elements are coupled together as shown in FIG. 2 .

The ring oscillator 260 generates an oscillation signal OUT NOISE . The ring oscillator 260 can be implemented by various techniques. In an example, the ring oscillator 260 includes an odd number of inverters I 1 -I 3 serially coupled together in a ring.

The switchable capacitor bank 270 includes a plurality of capacitors CS 1 -CS 12 that can be coupled to the ring oscillator 260 as capacitance load. In an example, each of the capacitors CS 1 -CS 12 is coupled with a switch (one of S 1 -S 12 ) in series. When the switch is closed, the capacitor is coupled to the ring oscillator 260 ; and when the switch is open, the capacitor is decoupled from the ring oscillator 260 . By controlling the switches S 1 -S 12 , the capacitance load of the ring oscillator 260 varies, and thus the frequency of the oscillation signal OUT NOISE varies.

The switches S 1 -S 12 can be implemented using various techniques, such as MOS transistors.

The noise generation control circuit 280 generates control signals to couple and decouple the plurality of capacitors CS 1 -CS 12 to the ring oscillator 260 .

In the FIG. 2 example, CS 1 -CS 4 are switchable capacitance load for the inverter I 1 , CS 5 -CS 8 are switchable capacitance load for the inverter I 2 , and CS 9 -CS 12 are switchable capacitance load for the inventor I 3 . In addition, in an example, CS 1 , CS 5 and CS 9 have the same capacitance, such as one-unit capacitance (1C); CS 2 , CS 6 and CS 10 have the same capacitance, such as two-unit capacitance (2C); CS 3 , CS 7 and CS 11 have the same capacitance, such as four-unit capacitance (4C); and CS 4 , CS 8 and CS 12 have the same capacitance, such as eight-unit capacitance (8C). S 1 -S 12 are respectively coupled with CS 1 -CS 12 .

The noise generation control circuit 280 generates controls signals CONTROL_ 1 to CONTROL_ 4 to control the switches S 1 -S 12 . For example, the control signal CONTROL_ 1 controls switches S 1 , S 5 and S 9 ; the control signal CONTROL_ 2 controls switches S 2 , S 6 and S 10 ; the control signal CONTROL_ 3 controls switches S 3 , S 7 and S 11 ; the control signal CONTROL_ 4 controls switches S 4 , S 8 and S 12 .

In an example, when a control signal is logic “0”, the corresponding switch is open, and when the control signal is logic “1”, the corresponding switch is closed. Thus, when the control signals CONTROL_ 1 to CONTROL_ 4 are “0000”, the capacitor CS 1 -CS 12 are decoupled from the ring oscillator 260 , and thus the oscillation signal OUT NOISE generated by the ring oscillator 260 has the highest frequency (f H ); and when the control signals CONTROL_ 1 to CONTROL_ 4 are “1111”, the capacitors CS 1 -CS 12 are coupled to the ring oscillator 260 , and thus the oscillation signal OUT NOISE generated by the ring oscillator 260 has the lowest frequency (f L ).

In an example, the noise generator 250 is suitably configured that the highest frequency f H is higher than the natural frequency f T , and the lowest frequency f L is lower than the natural frequency f T of the crystal component 111 .

During operation, the noise generation control circuit 280 varies the control signals CONTROL_ 1 to CONTROL_ 4 to vary the capacitance load in order to spread out the frequency of the oscillation signal OUT NOISE . Thus, energy is spread out in a frequency range that includes the natural frequency f T .

FIG. 3 shows a plot 300 of a power spectrum example for the oscillation signal OUT NOISE according to an embodiment of the disclosure. In the plot, the X-axis is frequency, and the Y-axis is power. The highest frequency f H is higher than the natural frequency f T , and the lowest frequency f L is lower than the natural frequency f T of the crystal component 111 .

In an example, during a design process for the IC chip 120 , a range of the natural frequency f T of the crystal component 111 is specified in a design specification, and thus is pre-known to designers. Then, the noise generator 250 is suitably designed that the highest frequency f H is higher than the upper limit of the specified range, and the lowest frequency f L is lower than the lower limit of the specified range of the crystal component 111 .

In the FIG. 3 example, the plot 300 includes a curve 300 shows energy spread out in the frequency range [f L ,f H ]. According to an aspect of the disclosure, the energy distribution on the natural frequency f T is higher than thermal noise.

It is noted that the noise generation control circuit 280 can use any suitably techniques, such as in a deterministic manner, in a random manner, in a pseudo random manner, and the like, to generate the control signals CONTROL_ 1 to CONTROL_ 4 , and to spread out energy in the frequency range.

FIG. 4 shows a diagram of a noise generation control circuit example 480 according to an embodiment of the disclosure. The noise generation control circuit 480 includes a plurality of D flip-flops D 1 -D 10 , and logic circuits, such as an XOR gate X 1 , and the like. The D flip-flops D 1 -D 10 and the logic circuits are suitably coupled together to generate the control signals CONTROL_ 1 to CONTROL_ 4 .

In the FIG. 4 example, the oscillation signal OUT NOISE is used as clock signals for the D flip-flops D 1 -D 10 .

FIG. 5 shows a flow chart outlining a process example 500 for the electronic system 100 to generate a clock signal according to embodiment of the disclosure. The process starts at S 501 and proceeds to S 510 .

At S 510 , the electronic system 100 receives power. In an example, when a power switch of the electronic system 100 is turned on, electric power is applied to the electronic system 100 and is suitably distributed in the electronic system 100 . In another embodiment, a portion of the electronic system 100 , such as the IC chip 120 , is powered off in a mode. When the electronic system 100 exits the mode, electric power is applied to the IC chip 120 .

At S 520 , a noise signal, such as the oscillation signal OUT NOISE with varying frequency, is intentionally generated, and injected into the crystal oscillator 110 to assist the crystal oscillator 110 to start oscillation. In an embodiment, the noise injection interface 140 is configured to couple the noise generator 150 to the crystal oscillator 110 at the time when the power is first received to inject the oscillation signal OUT NOISE into the crystal oscillator 110 . In an example, the energy of the noise signal spread on the natural frequency f T of the crystal oscillator 110 is higher than thermal noise. Thus, the start-up time for oscillation based on the noise signal is less than the start-up time for oscillation based on thermal noise. According to a simulation example of a 32 MHz crystal oscillator, based on the oscillation signal OUT NOISE generated by the noise generator 250 , the start-up time for oscillation is about 240 μs; and without injection of the noise signal, the start-up time for oscillation is about 500 μs. Further, tests are conducted in real electronic systems. The test results also show that a 32 MHz crystal oscillator can start up within 250 μs with the noise injection according to the disclosure.

At S 530 , the noise signal is decoupled from the crystal oscillator 110 . In an embodiment, the noise injection interface 140 is configured to decouple the noise generator 150 from the crystal oscillator 110 after a suitable time duration.

At S 540 , a clock signal is generated based on the oscillation signal generated by the crystal oscillator 110 . In an example, the clock signal is a system clock and is provided to various circuits in the electronic system 100 . Then, the process proceeds to S 599 and terminates.

It is noted that steps in the process 500 can be executed at the same time or in a different order. In an example, the noise signal is decoupled from the crystal oscillator 110 after the clock signal is generated.

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.