TWI390851B - Spread-spectrum generator - Google Patents

Description

Spread spectrum generator

The present invention relates to a spread spectrum generator, and more particularly to a spread spectrum generator with adjustable delay time.

In electronic circuits, spread spectrum generator devices are typically used to spread the frequency of the signal to avoid concentration of the signal's energy at a particular frequency. The frequency of the clock signal that is not used for the spread spectrum operation is a constant. The energy of the above clock signal is concentrated on a signal spectrum tone, and its electromagnetic-electromagnetic interference (EMI) is quite serious. For most electronic devices or packages, electromagnetic interference is a common but annoying disturbance that can interrupt, block, attenuate, or limit the performance of a device or an overall circuit.

In order to avoid electromagnetic interference from harmonics of a single frequency, spread spectrum techniques are applied. The spread spectrum represents the frequency of the modulated one-clock signal to distribute the energy of the clock signal to more spectral tones to reduce the electromagnetic interference of the clock signal. Therefore, the above-mentioned spread spectrum technique is one of the most popular methods for solving electromagnetic interference.

Accordingly, the present invention provides a spread spectrum generator capable of achieving frequency modulation of an input signal by adjusting a delay time of an input signal.

The invention provides a spread spectrum generator, which comprises a delay module and a control module. The delay module is controlled by a first control signal to delay an input signal by a delay time and thereby generate a delayed signal. The control module is coupled to the delay module for detecting a first edge of the delayed signal and thus generating the first control signal.

According to an embodiment of the invention, the delay module includes a digital analog converter and a first voltage controlled delay device. The digital analog converter converts a digital signal into a voltage control signal, wherein the digital signal is obtained by querying a lookup table based on the first control signal. The first voltage controlled delay device receives the input signal and is coupled to the digital analog converter for adjusting the delay time according to the voltage control signal to generate the delayed signal.

According to an embodiment of the invention, the delay module includes a plurality of first delay grids and a multiplexer. The plurality of first delay cells successively delay the input signals and respectively generate a plurality of candidate delay signals, wherein each of the first delay cells is controlled by a voltage control signal to delay the input signal by a delay time; and the multiplexer is first The control signal controls to select one of the candidate delay signals to be treated as a delayed signal.

According to an embodiment of the invention, the spread spectrum generator further includes a delay phase locked loop circuit. The delay-locked loop circuit is coupled to the first delay grid for locking a delay reference signal to a reference signal and generating a voltage control signal to adjust a delay time of each of the first delay bins.

According to an embodiment of the invention, the delay phase locked loop circuit includes a plurality of second delay cells, a phase detector and a charge pump circuit. Wherein the plurality of second delay cells successively delay the reference signal and thus generate a delayed reference signal, wherein each second delay bin is controlled by the voltage control signal to delay the reference signal by a delay time. The phase detector receives the reference signal and the delayed reference signal, and generates a second control signal according to a phase difference between the reference signal and the delayed reference signal. The charge pump circuit charges or discharges according to the second control signal and thus generates a voltage control signal.

According to an embodiment of the invention, the control module includes a detecting unit and a counting unit. The detecting unit detects a first edge of the delayed signal and generates a detecting signal. The counting unit is coupled to the detecting unit for counting the number of detecting signals to be generated and thus generating the first control signal.

In the present invention, the spread spectrum generator is based on a delay lattice structure and utilizes a voltage controlled delay line (VCDL) structure. With the VCDL structure, the spread spectrum generator has the flexibility to adjust the delay time. Furthermore, since the present invention employs a look-up table, we can adjust the delay time by changing the corresponding value in the lookup table.

The above described features and advantages of the present invention will be more apparent from the following description.

Reference will now be made in detail to the exemplary embodiments embodiments In addition, wherever possible, the same reference numerals in the drawings

1 is a schematic diagram of a spread spectrum operation for different modes of a clock signal. Please refer to FIG. 1. FIG. 1 illustrates three methods of spreading, including a method of abbreviating, a method of displaying, and a method of performing a center. The downscaling method expands the low spectrum, a raw clock signal spectrum is labeled as 100, and the abrupt clock signal spectrum is labeled 101. For example, the original clock signal has a period T, and the downscaling method shifts the period of the original clock signal by 0 to nTd, in other words, the period of the shifted clock signal has a period from T to T+nTd. On the other hand, the upscaling method expands the high spectrum and the spectrum of an up-going clock signal is labeled 102. For example, the original clock signal has a period T, and the upscaling method shifts the period of the original clock signal by 0 to (-nTd). In other words, the period of the shifted clock signal has a period from T to T-nTd. . In addition, the midamble method unfolds the nearby spectrum, and the spectrum of a midamble clock signal is labeled 103. For example, the original clock signal has a period T, and the midamble method shifts the period of the original clock signal (-nTd/2) to nTd/2, in other words, the period of the shifted clock signal has a period from T-( The period from nTd)/2 to T+(nTd)/2.

For example, Figure 2 illustrates an expanded range of input signals in the midamble method. Referring to FIG. 2, the period of the input signal is periodically expanded from 5Td to (-5Td). Therefore, in order to reduce the electromagnetic interference of the input signal, the energy of the input signal is distributed to a wider frequency range. In order to implement a circuit that can perform the above-described spread spectrum operation, several circuits according to embodiments of the present invention are disclosed below.

3 is a circuit diagram of a spread spectrum generator in accordance with an embodiment of the present invention. Referring to FIG. 3, the spread spectrum generator 300 includes a delay module 310 and a control module.

The delay module 310 receives an input signal and a control signal CON1, wherein the delay module 310 delays the input signal by a delay time according to the control signal CON1. The input signal delayed by the delay module 310 is treated as a delayed signal. The control module 320 is coupled to the delay module 310, and the control module 320 receives the delay signal and generates a control signal CON1 according to the first edge, for example, a positive edge of the delayed signal. As shown in FIG. 4, another possible implementation of the control module 320 will be described below.

4 is a circuit diagram of a control module in accordance with an embodiment of the present invention. Referring to FIG. 4 , the spread spectrum generator 400 includes a delay module 310 and a control module 420 . The control module 420 includes a detecting unit 421 and a counting unit 422 . The detecting unit 421 receives the delay signal and detects a first edge of the delayed signal, for example, a positive edge of the delayed signal, and the detecting unit 421 generates a detection signal. The counting unit 422 is coupled to the detecting unit 421 and receives the detection signal generated by the detecting unit 421. In addition, the counting unit 422 calculates the number of detection signals to determine which cycle the delay signal is currently in, and the counting unit 422 generates a control signal CON1 to adjust the delay module 310.

For example, FIG. 5 illustrates a waveform of an input signal and a delayed signal in a spread spectrum generator according to an embodiment of the present invention. Referring to FIG. 4 and FIG. 5, an input signal received by the delay module 310 has a period T. When the delay module 310 receives the positive edge of the input signal, the delay module 310 delays the input signal by a delay time Td and outputs the delayed input signal as a delayed signal. In addition, the detecting unit 421 receives the delay signal and detects the positive edge of the delayed signal, and then the detecting unit 421 generates a detecting signal. The counting unit 422 calculates the number of detection signals, in other words, a detection signal is received, and generates a control signal CON1 to adjust the delay time of the delay module 310, for example, the delay time is adjusted to 2Td. The delay module 310 delays the input signal by a different delay time in each positive edge according to the control signal CON1. In other words, according to the control signal CON1, the delay time is selected, wherein the control module 420 receives the delay signal and calculates the delay. The number of positive edges of the signal and thus a control signal CON1. Thus, when the delay module 310 receives the input signal of the ^{2 nd, 3 rd, 4 th} , and 5 ^th positive edge of the input signal delay modules 310 each delay time 2Td, 4Td, 7Td and 11Td, and outputs the delay input The signal acts as a delayed signal.

As shown in FIG. 6, another possible implementation of the delay module 310 will be described below. 6 is a circuit diagram of a delay module in accordance with an embodiment of the present invention. Referring to FIG. 6 , the spread spectrum generator 600 includes a delay module 610 and a control module 320 . The delay module 610 includes a voltage control delay device 611 , a digital analog converter (DAC ) 612 , and a lookup table 613 . For example, the function of the control module 320 is the same as that of the control module 420. The voltage control delay means 611 receives the input signal and adjusts the delay time CON2 in accordance with a voltage control signal to generate a delayed signal. The voltage controlled delay device 611 can delay the input signals respectively located at different positive edges by a selected delay time to perform a spread spectrum operation. Therefore, the frequency of the input signal performed in conjunction with the spread spectrum operation is not a constant but an unfolded range of frequencies.

The digital analog converter 612 converts a digital signal into a voltage control signal CON2, wherein the digital signal is obtained by querying the lookup table 613 based on the control signal CON1. For example, control module 320 can generate control signal CON1 based on the number of positive edges of the delayed signal. The lookup table 613 receives the control signal CON1, and the control signal CON1 is treated as an index to query the lookup table 613. Next, the lookup table 613 sends a digital signal to the digital analog converter 612 based on the result of the query lookup table 613.

It is worth mentioning that the lookup table 613 sends a digital signal according to the control signal CON1, wherein the relationship between the digital signal and the control signal CON1 may not be a linear curve. Since the voltage control delay means 611 adjusts the delay time based on the voltage control signal CON2 converted from the digital signal, by changing the relationship between the digital signal and the control signal CON1, we can adjust the delay time.

Referring to FIG. 3, one of the other possible implementations of the delay module 310 will be described below, as shown in FIG. 7 is a circuit diagram of a delay module in accordance with an embodiment of the present invention. Referring to FIG. 7 , the spread spectrum generator 700 includes a delay module 710 and a control module 320 . The delay module 710 includes a plurality of delay grids 711 and a multiplexer 712 . For example, the control module 320 has the same function as the control module 420. The plurality of delay cells 711 successively delay the input signal by a delay time Td and respectively generate a plurality of candidate delay signals, wherein the delay time Td can be adjusted by a voltage control signal Vtrl. The multiplexer 712 is controlled by the control signal CON1 to select one of the candidate delay signals as a delayed signal. In other words, each candidate delay signal has a different period, from T+(nTd)/2 to T-(nTd)/2, where T is the period of the input signal, and n is determined by the number of delay bins 711.

Referring to FIG. 7, one of the other possible implementations of the spread spectrum generator 700 further includes a delay phase locked loop circuit, as shown in FIG. FIG. 8 is a circuit diagram of a spread spectrum generator in accordance with an embodiment of the present invention. Referring to FIG. 8 , the spread spectrum generator 800 includes a delay module 710 , a control module 320 , and a delay lock loop circuit 830 . The delay module 710 includes a plurality of delay grids 711 and a multiplexer 712 . The plurality of delay bins 711 successively delay the input signal by a delay time Td and respectively generate a plurality of candidate delay signals, wherein each of the delay bins 711 is controlled by a voltage control signal Vtrl to delay the input signal by a delay time Td. The multiplexer 712 is controlled by the control signal CON1 to select one of the candidate delay signals as a delayed signal. The delay-locked loop circuit 830 is coupled to the delay grid 711 to lock a delay reference signal (Dref) to a reference signal (ref) and to generate a voltage control signal Vtrl to adjust the delay time Td of each delay bin 711.

For example, the delay phase locked loop circuit 830 includes an N-spaced VCDL 831, a phase detector 832, and a charge pump circuit 833. The N-interval VCDL 831 successively delays the reference signal and thus produces a delayed reference signal, wherein the N-interval VCDL 831 is controlled by the voltage control signal Vtrl to delay the reference signal by a delay time. The phase detector 832 receives the reference signal and the delayed reference signal, and the phase detector 832 generates a control signal CON2 according to a phase difference between the reference signal and the delayed reference signal. The charge pump circuit 833 charges or discharges according to the control signal CON2 and thus generates the voltage control signal.

Therefore, we can adjust the delay time Td of the delay lattice 711 through the delay phase locked loop circuit 830, and the reference signal for delaying the phase locked loop circuit 830 is regarded as a preset signal for generating the delay time of the delay lattice 711. Td.

In summary, the spread spectrum generator of the present invention adjusts the frequency of an input signal by delaying the input signal by a delay time. In conjunction with the spread spectrum generator, EMI caused by a single frequency harmonic can be greatly reduced. In addition, a delay-locked loop circuit is applied to set the delay time of the delay module so that we can change the spread range of the input signal by selecting the period of the reference signal of the delay-locked loop circuit.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100. . . original

101. . . Exhibition

102. . . Exhibition

103. . . Exhibition

310, 610, 710. . . Delay module

320, 420. . . Control module

421. . . Detection unit

422. . . Counting unit

611. . . Voltage controlled delay device

612. . . DAC

613. . . Query list

711. . . Delay lattice

712. . . Multiplexer

830. . . Delayed phase-locked loop circuit

831. . . N-spaced VCDL

832. . . Phase detector

833. . . Voltage pump circuit

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the invention and, in conjunction with the embodiments,

1 is a schematic diagram of a conventional spread spectrum operation for different ways of clock signals.

Figure 2 illustrates an expanded range of input signals in the mid-expansion method.

3 is a circuit diagram of a spread spectrum generator in accordance with an embodiment of the present invention.

4 is a circuit diagram of a control module in accordance with an embodiment of the present invention.

FIG. 5 is a diagram showing waveforms of an input signal and a delayed signal in a spread spectrum generator according to an embodiment of the present invention.

6 is a circuit diagram of a delay module in accordance with an embodiment of the present invention.

7 is a circuit diagram of a delay module in accordance with an embodiment of the present invention.

FIG. 8 is a circuit diagram of a spread spectrum generator in accordance with an embodiment of the present invention.

320. . . Control module

710. . . Delay module

711. . . Delay lattice

712. . . Multiplexer

830. . . Delayed phase-locked loop circuit

831. . . N-spaced VCDL

832. . . Phase detector

833. . . Voltage pump circuit

Claims (5)

A spread spectrum generator includes: a delay module controlled by a first control signal to delay an input signal by a delay time and thereby generating a delay signal; and a control module coupled to the delay module a first edge for detecting the delayed signal, and thus generating the first control signal, wherein the delay module includes: a plurality of first delay cells, successively delaying the input signal, and generating a plurality of candidates respectively a delay signal, wherein each first delay bin is controlled by a voltage control signal to delay the input signal by a delay time; and a multiplexer controlled by the first control signal to select one of the candidate delay signals to be Make this delay signal. The spread spectrum generator of claim 1, wherein the spread spectrum generator further comprises: a delay phase locked loop circuit coupled to the first delay grids for locking a delay reference signal The signal is referenced and the voltage control signal is generated to adjust the delay time for each first delay bin. The spread spectrum generator of claim 2, wherein the delay phase locked loop circuit comprises: a plurality of second delay cells, successively delaying the reference signal, and thus generating the delayed reference signal, wherein each The second delay grid is controlled by the voltage control signal to delay the reference signal by the delay time; a phase detector receives the reference signal and the delayed reference signal, and according to a phase between the reference signal and the delayed reference signal Poor generation a second control signal; and a charge pump circuit for charging or discharging according to the second control signal and thereby generating the voltage control signal. The spread spectrum generator of claim 3, wherein the delay time is a ratio of a period of the reference signal to a magnitude of the second delay lattice. The spread spectrum generator of claim 1, wherein the control module comprises: a detecting unit that detects a first edge of the delayed signal and generates a detection signal; and a counting unit, The detecting unit is coupled to the counter to count the number of the detection signals to be generated and thus generate the first control signal.