Signal processing system and method thereof

A signal processing system includes an adjustable filter, a signal difference calculating unit, a determining unit and a selecting unit. The adjustable filter is configured to receive a digital signal outputted from an analog-to-digital converter, and filter the digital signal to generate a filtered signal. The signal difference calculating unit is configured to calculate and output a signal difference value between the digital signal and the filtered signal. The determining unit is configured to compare the signal difference value with a predetermined threshold value, to generate a comparison result, and generate a selection signal and a bandwidth adjustment signal according to the comparison result. The selecting unit is configured to receive the digital signal and the filtered signal, and output one of the digital signal and the filtered signal according to the selection signal. The bandwidth of the adjustable filter can be adjusted according to the bandwidth adjustment signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Taiwan Patent Application No. 107141229, filed on Nov. 20, 2018, in the Taiwan Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal processing system, more particularly to a signal processing system which is able to improve a signal-to-noise ratio of an analog-to-digital converter, and a method thereof.

2. Description of the Related Art

Analog-to-digital converters (ADCs) are used to convert analog signals into digital signals. In practical applications, the analog signals possibly contain data signals and environmental noise. During conversion process, the analog-to-digital converter also generates quantization noise and circuit noise. As a result, the converted digital signal is affected by environmental noise, quantization noise, and circuit noise.

In general, the signal-to-noise ratio (SNR) defined in the specification of an analog-to-digital converter is for the ratio of data signal to quantization noise and circuit noise. In order to improve the signal-to-noise ratio, a filter can be built in the analog-to-digital converter and the bandwidth of the built-in filter must cover the sampling frequency of the analog-to-digital converter, otherwise the performance of the analog-to-digital converter is affected by the built-in filter. As a result, when the frequency of the signal is low, the built-in filter still cannot effectively improve the signal-to-noise ratio.

For the above reasons, in practical applications, the digital signal output by the analog digital converter needs to be processed by software to eliminate environmental noise.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problem, the present invention provides signal processing system and a method thereof, to effectively improve the signal-to-noise ratio of an analog-to-digital converter.

According to an embodiment, the present invention provides a signal processing system adapted to an analog-to-digital converter and comprising an adjustable filter, a signal difference calculating unit, a determining unit and a selecting unit. The adjustable filter is configured to receive a digital signal outputted from the analog-to-digital converter, and filter the digital signal to generate a filtered signal. The signal difference calculating unit is configured to calculate and output a signal difference value between the digital signal and the filtered signal. The determining unit is configured to compare the signal difference value with a preset threshold value to generate the comparison result, and generate a selection signal and a bandwidth adjustment signal according to the comparison result. The selecting unit is configured to receive the digital signal and the filtered signal, and output one of the digital signal and the filtered signal according to the selection signal. A bandwidth of the adjustable filter is adjusted according to the bandwidth adjustment signal.

Preferably, the adjustable filter is an adjustable low-pass filter.

Preferably, when the signal difference value is higher than the preset threshold value, the selecting unit outputs the digital signal according to the selection signal, and the adjustable filter extends the bandwidth thereof according to the bandwidth adjustment signal, and when the signal difference value is lower than the preset threshold value, the selecting unit outputs the filtered signal according to the selection signal, and the adjustable filter narrows the bandwidth thereof according to the bandwidth adjustment signal.

Preferably, the preset threshold value comprises a first threshold value and a second threshold value, the determining unit compares the signal difference value with the first threshold value and the second threshold value, respectively, to generate a comparison result and generates a selection signal and the bandwidth adjustment signal according to the comparison result; and the first threshold value is higher than the second threshold value; when the signal difference value is higher than the first threshold value, the selecting unit outputs the digital signal according to the selection signal, and the adjustable filter extends the bandwidth thereof according to the bandwidth adjustment signal, and when the signal difference value is lower than the first threshold value and higher than the second threshold value, the selecting unit outputs the filtered signal according to the selection signal, and the adjustable filter narrows the bandwidth thereof according to the bandwidth adjustment signal, and when the signal difference value is lower than the second threshold value, the selecting unit outputs the filtered signal according to the selection signal, and the adjustable filter keeps the bandwidth thereof.

Preferably, the adjustable filter comprises a first adjustable filter and a second adjustable filter configured to filter the digital signal to generate a first filtered signal and a second filtered signal, respectively, and a bandwidth of the first adjustable filter is broader than a bandwidth of the second adjustable filter; the signal difference calculating unit calculates and outputs a first signal difference value and a second signal difference value between the digital signal and the first filtered signal and the second filtered signal, respectively, and the determining unit compares the first signal difference value and the second signal difference value with a preset threshold value to generate the comparison result, and generate the selection signal, a first bandwidth adjustment signal and a second bandwidth adjustment signal according to the comparison result.

Preferably, when the first signal difference value and the second signal difference value are higher than the preset threshold value, the selecting unit outputs the digital signal according to the selection signal, and the first adjustable filter extends the bandwidth according to the first bandwidth adjustment signal; when the first signal difference value is lower than the preset threshold value and the second signal difference value is higher than the preset threshold value, the selecting unit outputs the first filtered signal according to the selection signal, and the first adjustable filter narrows the bandwidth according to the first bandwidth adjustment signal, and the second adjustable filter extends the bandwidth according to the second bandwidth adjustment signal; when both of the first signal difference value and the second signal difference value are lower than the preset threshold value, the selecting unit outputs the second filtered signal according to the selection signal, and the second adjustable filter narrows the bandwidth thereof according to the second bandwidth adjustment signal.

Preferably, the preset threshold value comprises a first threshold value and a second threshold value, the determining unit compares the first signal difference value and the second signal difference value with the first threshold value and the second threshold value, and the first threshold value is higher than the second threshold value; when both of the first signal difference value and the second signal difference value are higher than the first threshold value, the selecting unit outputs the digital signal according to the selection signal, and the first adjustable filter extends the bandwidth thereof according to the first bandwidth adjustment signal; when both of the first signal difference value and the second signal difference value are lower than the first threshold value, the selecting unit outputs the second filtered signal according to the selection signal, and the second adjustable filter narrows the bandwidth thereof according to the second bandwidth adjustment signal; when the first signal difference value is lower than the first threshold value and higher than the second threshold value and the second signal difference value is higher than the first threshold value, the selecting unit outputs the first filtered signal according to the selection signal, and the first adjustable filter narrows the bandwidth thereof according to the first bandwidth adjustment signal, and the second adjustable filter extends the bandwidth thereof according to the second bandwidth adjustment signal; when the first signal difference value is lower than the second threshold value, the selecting units output the first filtered signal according to the selection signal, and the first adjustable filter keeps the bandwidth thereof; when the second signal difference value is lower than the second threshold value, the selecting unit outputs the second filtered signal according to the selection signal, and the second adjustable filter keeps the bandwidth thereof.

According to an embodiment, the present invention provides a signal processing method adapted to an analog-to-digital converter outputting a digital signal. The signal processing method comprises steps of using an adjustable filter to filter the digital signal, to generate a filtered signal; calculating and outputting a signal difference value between the digital signal and the filtered signal; comparing the signal difference value with a preset threshold value, to generate the comparison result, and then generating a selection signal and a bandwidth adjustment signal according to the comparison result; according to the selection signal, outputting one of the digital signal and the filtered signal; and adjusting a bandwidth of the adjustable filter according to the bandwidth adjustment signal.

According to an embodiment, the present invention provides a signal processing system adapted to an analog-to-digital converter, and comprising a plurality of filters, a signal difference calculating unit, a determining unit and a selecting unit. The plurality of filters are configured to receive a digital signal outputted from the analog-to-digital converter, and filter the digital signal to generate a plurality of filtered signals. The plurality of filters have different bandwidths. The signal difference calculating unit is configured to calculate and output a plurality of signal difference values between the digital signal and the plurality of filtered signals, and output a minimal signal difference value among the plurality of signal difference values, and output the filtered signal corresponding to the minimal signal difference value. The determining unit is configured to compare the minimal signal difference value with the preset threshold value to generate the comparison result, and then generate a selection signal according to the comparison result. The selecting unit is configured to receive the digital signal and the filtered signal corresponding to the minimal signal difference value, and output one of the digital signal and the filtered signal corresponding to the minimal signal difference value, according to the selection signal.

According to an embodiment, the present invention provides a signal processing system adapted to an analog-to-digital converter and comprising a plurality of filters, a signal difference calculating unit, a determining unit and a selecting unit. The plurality of filters are configured to receive a digital signal outputted from the analog-to-digital converter, and filter the digital signal to generate a plurality of filtered signals. The plurality of filters have different bandwidths. The signal difference calculating unit are configured to calculate and output a plurality of signal difference values between the digital signal and the plurality of filtered signals, and output a minimal signal difference value among the plurality of signal difference values, and a filter ID code corresponding to the minimal signal difference value. The determining unit is configured to compare the minimal signal difference value with the preset threshold value to generate a comparison result, and then generate a selection signal according to the comparison result and the filter ID code. The selecting unit is configured to receive the digital signal and the filtered signal, and output one of the digital signal and the plurality of filtered signals according to the selection signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer toFIG. 1, which is a block diagram of an embodiment of a signal processing system of the present invention. As shown inFIG. 1, the signal processing system of the present invention is applicable to an analog-to-digital converter10, and the signal processing system can comprise an adjustable filter20, a signal difference calculating unit30, a determining unit40, and a selecting unit50. The analog-to-digital converter10can receive an analog signal101, and convert the analog signal101into a digital signal102.

The adjustable filter20is configured to receive the digital signal102outputted from the analog-to-digital converter10, and filter the received digital signal102, so as to generate a filtered signal201. Preferably, the adjustable filter20can be an adjustable low-pass filter which can be a low-pass filter with a bandwidth adjusted by an external control signal.

The signal difference calculating unit30is configured to calculate and output a signal difference value301between the digital signal102and the filtered signal201. In an actual application, the digital signal102can comprise a plurality of bits, and the number of bit of the filtered signal201is the same as that of the digital signal102, and the signal difference value301can comprise at least one bit, for example, the signal difference value301can be a least significant bit (LSB) where the bit of the digital signal102is different from that of the filtered signal201, or the number of the least significant bit.

For example, when a resolution of the analog-to-digital converter10is10, it indicates that the number of bits of the digital signal102is ten, for example, the digital signal102can be “1101100111” and filtered signal201can be “1101001010”, the least significant bits indicative of difference between the digital signal102and the filtered signal201is are “100111”, so the signal difference value301can be “100111” or six, and it indicates that the filtering process performed by the adjustable filter20affects the sixth bit of the digital signal102.

The determining unit40is configured to compare the signal difference value301and a preset threshold value49to generate a comparison result, and also generate a selection signal411and a bandwidth adjustment signal412according to the comparison result. The selecting unit50is configured to receive the digital signal102and the filtered signal201, and output one of the digital signal102and the filtered signal201according to the selection signal411.

The bandwidth of the adjustable filter20can be adjusted according to the bandwidth adjustment signal412. When the signal difference value301is higher than the preset threshold value49, it indicates that the adjustable filter20filters out the data signal of the digital signal102, so the selecting unit50can output the digital signal102according to the selection signal411, and the adjustable filter20can extend the bandwidth thereof according to the bandwidth adjustment signal412, thereby preventing filtering out the data signal of the digital signal102.

When the signal difference value301is lower than the preset threshold value49, it indicates that the adjustable filter20filters out the noise of the digital signal102only, so the selecting unit50can output the filtered signal201according to the selection signal411, and the adjustable filter20can narrow the bandwidth thereof according to the bandwidth adjustment signal412, thereby filtering out more noise. Preferably, the selecting unit50can be implemented by a multiplexer.

In an actual application, the analog signal101possibly include the data signal and the environmental noise, and during the data conversion the analog-to-digital converter10generates the quantization noise and the circuit noise, so the digital signal102is possibly affected by environmental noise, quantization noise, and circuit noise.

In an embodiment, when the adjustable filter20can filter the digital signal102; particularly, when the frequency of the data signal is lower than the frequency of the environmental noise, the adjustable filter20can be implemented by a low-pass filter, to filter out the high-frequency environmental noise. Furthermore, since the determining unit40can adjust the bandwidth of the adjustable filter20by a feedback scheme, when the frequency of the data signal changes, the bandwidth of the adjustable filter20can be adjusted adaptively, for example, the bandwidth can be extended to prevent the data signal from being filtered out; or, the bandwidth can be narrowed to filter out more environmental noise effectively.

Please refer toFIG. 2, which is a block diagram of another embodiment of a signal processing system of the present invention. As shown inFIG. 2, the signal processing system can be adapted to the analog-to-digital converter10, and the signal processing system can comprise an adjustable low-pass filter20a,a signal difference calculating unit30, a determining unit40aand a selecting unit50. The analog-to-digital converter10can receive an analog signal101, and convert the received analog signal101into the digital signal102. The difference between the embodiment shown inFIG. 2and the aforementioned embodiment is that the embodiment shown inFIG. 2includes the adjustable low-pass filter20a,and the determining unit40ausing two threshold values.

In the embodiment, when the threshold values used in the determining unit40acomprise a first threshold value401and a second threshold value402, and the first threshold value401is higher than the second threshold value402. The determining unit40acompares the signal difference value301with the first threshold value401and the second threshold value402, to generate a comparison result. The determining unit40acan generate the selection signal411and the bandwidth adjustment signal412according to the comparison result.

When the signal difference value301is higher than the first threshold value401, it indicates that the adjustable low-pass filter20afilters out the data signal of the digital signal102, so the selecting unit50can output the digital signal102according to the selection signal411, and the adjustable filter20can extend the bandwidth according to the bandwidth adjustment signal412.

When the signal difference value301is lower than the first threshold value401and higher than the second threshold value402, it indicates that the adjustable low-pass filter20adoes not filter out the data signal of the digital signal102and there is much room to filter out the environmental noise, so the noise contained in the filtered signal201is less than that of the digital signal, and the selecting unit50can output the filtered signal201according to the selection signal411, thereby increasing the signal-to-noise ratio of the analog-to-digital converter10. Next, the adjustable low-pass filter20acan narrow the bandwidth thereof according to the bandwidth adjustment signal412, so as to filter out more environmental noise.

When the signal difference value301is lower than the second threshold value402, it indicates that the environmental noise of the digital signal102is filtered out effectively, so the selecting unit50can output the filtered signal201according to the selection signal411, thereby increasing the signal-to-noise ratio of the analog-to-digital converter10. Next, the adjustable low-pass filter20acan keep the bandwidth thereof.

For example, when a resolution of the analog-to-digital converter10is10, it indicates that the number of bits of the digital signal102is ten, and the first threshold value401can be 5-bit data or five, and the second threshold value402can be 3-bit data or three, and the initial bandwidth of the adjustable low-pass filter20ais from 0 Hz to 6 KHz and can be adjusted to 10 KHz. For example, the digital signal102can be “1101100111”, and the filtered signal201can be “1101001010”, the least significant bits indicative of the difference between the digital signal102and the filtered signal201are “100111” which is 6-bit and higher than the first threshold value401, so the selecting unit50can output the digital signal102, and the adjustable low-pass filter20aextends the bandwidth thereof to 6 KHz. When the filtered signal201is “1101101010”, and the signal difference value301is “0111” which is 4-bit and lower than first threshold value401and higher than the second threshold value402, the selecting unit50can output the filtered signal201, and the adjustable low-pass filter20anarrows the bandwidth thereof to 4 K Hz; when the filtered signal201is “1101100100” and the signal difference value301is “11” which is 2-bit and lower than the second threshold value402, the selecting unit50can output the filtered signal201, and the adjustable low-pass filter20acan keep the bandwidth thereof.

Please refer toFIG. 3, which is a flowchart showing the steps in an operation of an embodiment of a signal processing method of the present invention. As shown in FIG.3, the signal processing method can be adapted to the analog-to-digital converter, and include steps S31to S36. In a step S31, a digital signal outputted from the analog-to-digital converter is received. In a step S32, the adjustable filter is used to filter the digital signal, to generate the filtered signal. In a step S33, the signal difference value between the digital signal and the filtered signal is calculated and outputted. In a step S34, the signal difference value is compared with the preset threshold value, to generate the comparison result, and the selection signal and the bandwidth adjustment signal are generated according to the comparison result. When the signal difference value is higher than the preset threshold value, the flow enters a step S35, and when the signal difference value is lower than the preset threshold value, the flow enters a step S36.

In a step S35, the digital signal is outputted according to the selection signal, and the bandwidth of the adjustable filter is extended according to the bandwidth adjustment signal.

In a step S36, the filtered signal is outputted according to the selection signal, and the bandwidth of the adjustable filter is narrowed according to the bandwidth adjustment signal.

Please refer toFIGS. 4 and 5, which are a block diagram of another embodiment of a signal processing system of the present invention, and a block diagram of an embodiment of a signal difference calculating unit of a signal processing system of the present invention. As shown inFIG. 4, the signal processing system can comprise a first adjustable filter21, a second adjustable filter22, a signal difference calculating unit31, a determining unit41and a selecting unit50. The first adjustable filter21and the second adjustable filter22can filter the digital signal102to generate the first filtered signal211and the second filtered signal221, respectively. In the embodiment, the bandwidth of the first adjustable filter21is higher than the bandwidth of the second adjustable filter22.

The signal difference calculating unit31can calculate and output a first signal difference value311between the digital signal102and the first filtered signal211, and a second signal difference value312between the digital signal102and the second filtered signal221. As shown inFIG. 5, the signal difference calculating unit31can comprise a first signal difference calculating unit31aand a second signal difference calculating unit31b.The first signal difference calculating unit31ais configured to compare the digital signal102with the first filtered signal211to find the different bits between the digital signal102and the first filtered signal211, so as to generate a first signal difference value311. The second signal difference calculating unit3lb is configured to compare the digital signal102with the second filtered signal221to find the different bits between the digital signal102and the second filtered signal221, so as to generate a second signal difference value312.

The determining unit41can compare the first signal difference value311and the second signal difference value312with a preset threshold value, to generate a comparison result, and then generate a selection signal420, a first bandwidth adjustment signal421and a second bandwidth adjustment signal422according to the comparison result.

In an embodiment, the number of the preset threshold value is one. When both of the first signal difference value311and the second signal difference value312are higher than the preset threshold value, the selecting unit50can output the digital signal102according to the selection signal420, and the first adjustable filter21can extend the bandwidth thereof according to the bandwidth adjustment signal412.

When the first signal difference value311is lower than the preset threshold value and the second signal difference value312is higher than the preset threshold value, the selecting unit50can output the first filtered signal211according to the selection signal411, and the first adjustable filter21can narrow the bandwidth thereof according to the bandwidth adjustment signal412, and the second adjustable filter22can extend the bandwidth thereof according to the bandwidth adjustment signal412.

When both of the first signal difference value311and the second signal difference value312is lower than the preset threshold value49, when the selecting unit50output the second filtered signal221according to the selection signal411, and when the second adjustable filter22can narrow the bandwidth thereof according to the bandwidth adjustment signal412.

In another embodiment, the number of the preset threshold values is multiple. For example, the preset threshold values can include a first threshold value401and a second threshold value402, and the first threshold value401is higher than the second threshold value402. The determining unit41can compare the first signal difference value311and the second signal difference value312with the first threshold value401and the second threshold value402to generate the comparison result, and then generate the selection signal420, the first bandwidth adjustment signal421and the second bandwidth adjustment signal422according to the comparison result.

When the first signal difference value311is higher than the first threshold value401, the selecting unit50can output the digital signal102according to the selection signal420, and the first adjustable filter21can extend the bandwidth thereof according to the first bandwidth adjustment signal421. When the second signal difference value312is lower than the first threshold value401, the selecting unit50can output the second filtered signal221according to the selection signal420, and the second adjustable filter22can narrow the bandwidth thereof according to the second bandwidth adjustment signal422.

When the first signal difference value311is lower than the second threshold value402, the selecting unit50can output the first filtered signal211according to the selection signal420, and the first adjustable filter21keeps the bandwidth thereof. When the second signal difference value312is lower than the second threshold value402, the selecting unit50can output the second filtered signal221according to the selection signal420, and the second adjustable filter22can keep the bandwidth thereof.

When the first signal difference value311is lower than the first threshold value401, and is higher than the second threshold value402, the selecting unit50can output the first filtered signal211according to the selection signal420, and the first adjustable filter21can narrow the bandwidth thereof according to the first bandwidth adjustment signal421, and the second adjustable filter22can narrow the bandwidth thereof according to the second bandwidth adjustment signal422.

Please refer toFIG. 6, which is a flowchart showing the steps in an operation of another embodiment of a signal processing method of the present invention. As shown inFIG. 6, the signal processing method is adapted to the analog-to-digital converter and comprise steps S61to S66. In a step S61, the digital signal outputted from the analog-to-digital converter is received. In a step S62, the first adjustable filter and the second adjustable filter are used to filter the digital signal, to generate the first filtered signal and the second filtered signal, respectively.

In a step S63, the digital signal, a first signal difference value and a second signal difference value between the first filtered signal and the second filtered signal are calculated and outputted, respectively, the first signal difference value and second signal difference value are then compared with a first threshold value and a second threshold value, respectively, to generate the comparison result, and the selection signal, the first bandwidth adjustment signal and the second bandwidth adjustment signal are then generated according to the comparison result. The first threshold value is higher than the second threshold value.

In a step S64, it is determined whether the first signal difference value or the second signal difference value is lower than the second threshold value, and when at least one of the first signal difference value and the second signal difference value is lower than the second threshold value, the flow enters a step S65; otherwise, the flow enters a step S64a.In a step S65, the first filtered signal or the second filtered signal is outputted according to the selection signal, and at least one of the first adjustable filter or the second adjustable filter keeps the bandwidth thereof.

In step S64a,it is determined whether the first signal difference value is higher than the first threshold value, and when the first signal difference value is higher than the first threshold value, the flow enters a step S65a;otherwise, the flow enters a step66. In the step S65a,the digital signal is outputted according to the selection signal, and the first adjustable filter extends the bandwidth thereof according to the first bandwidth adjustment signal.

In a step S66, it is determined whether the second signal difference value is lower than the first threshold value, and when the second signal difference value is lower than the first threshold value, the flow enters a step S67; otherwise, the flow enters a step S68. In the step S67, the second filtered signal is outputted according to the selection signal, and the second adjustable filter can narrow the bandwidth thereof according to the second bandwidth adjustment signal. In the step S68, the first filtered signal is outputted according to the selection signal, and the first adjustable filter can narrow the bandwidth thereof according to the first bandwidth adjustment signal, and the second adjustable filter can extend the bandwidth thereof according to the second bandwidth adjustment signal.

Please refer toFIG. 7, which is a block diagram of another embodiment of a signal processing system of the present invention. As shown inFIG. 7, the signal processing system can be adapted to the analog-to-digital converter, and comprise a first filter61, a second filter62, a third filter63, a fourth filter64, a minimal-difference determining unit70, a determining unit43and a selecting unit50. The first filter61, the second filter62, the third filter63, the fourth filter64have different bandwidths, for example, the bandwidth of the first filter61is from 0 Hz to 5 K Hz, the bandwidth of the second filter62is from 0 Hz to 6 K Hz, the bandwidth of the third filter63is 0 Hz to 7 K Hz, and the bandwidth of the fourth filter64is from 0 Hz to 8 KHz. The first filter61, the second filter62, the third filter63, the fourth filter64are configured to receive the digital signal102outputted from the analog-to-digital converter10and filter the digital signal102, to generate a first filtered signal611, a second filtered signal621, a third filtered signal631and a fourth filtered signal641, respectively.

The minimal-difference determining unit70can calculate a plurality of signal difference values between the digital signal102and the first filtered signal611, the second filtered signal621, between the third filtered signal631and the fourth filtered signal641, and output the minimal signal difference value701among the plurality of signal difference values, and also output a filtered signal702corresponding to the minimal signal difference value701. For example, when the signal difference value between the digital signal102and first filtered signal611is the minimal value among the plurality of signal difference values, the minimal-difference determining unit70outputs the first filtered signal611as the filtered signal702.

The determining unit43can compare the minimal signal difference value701with the preset threshold value431to generate the comparison result, and then generate the selection signal432according to the comparison result. The selecting unit50can receive the digital signal102and the filtered signal201, and output one of the digital signal102and the filtered signal702according to the selection signal411. When the minimal signal difference value701is higher than the preset threshold value431, the selecting unit50outputs the digital signal102, and when the minimal signal difference value701is lower than or equal to the preset threshold value431, the selecting unit50can output the filtered signal702.

The difference between the embodiment shown inFIG. 7and aforementioned embodiments is that the embodiments shown inFIG. 7uses a plurality of filters, so that it is not necessary to use the adjustable filter and the feedback scheme to adjust the filter bandwidth.

Please refer toFIG. 8, which is a block diagram of another embodiment of a signal processing system of the present invention. As shown inFIG. 8, the signal processing system can be adapted to the analog-to-digital converter, and the signal processing system can comprise the first filter61, the second filter62, the third filter63, the fourth filter64, a minimal-difference determining unit70a,the determining unit43and the selecting unit50. The first filter61, the second filter62, the third filter63, the fourth filter64have different bandwidths.

The first filter61, the second filter62, the third filter63, the fourth filter64and receive the digital signal102outputted from the analog-to-digital converter10, and filter the digital signal102to generate the first filtered signal611, the second filtered signal621, the third filtered signal631and the fourth filtered signal641, respectively.

The minimal-difference determining unit70acan calculate the plurality of signal difference values between the digital signal102and the first filtered signal611, the second filtered signal621, the third filtered signal631and the fourth filtered signal641, and output the minimal signal difference value701among the plurality of signal difference values, and output a filter ID code703corresponding to the minimal signal difference value701. For example, when the signal difference value between the and the digital signal102and first filtered signal611is the minimal value among the plurality of signal difference values, the minimal-difference determining unit70acan output “1” as the filter ID code703.

The determining unit43can compare the minimal signal difference value701with the preset threshold value431to generate the comparison result, and then generate the selection signal411according to the comparison result and the filter ID code703. The selecting unit50can receive the digital signal102, the first filtered signal611, the second filtered signal621, the third filtered signal631and the fourth filtered signal641, and output one of the digital signal102, the first filtered signal611, the second filtered signal621, the third filtered signal631, and the fourth filtered signal641according to the selection signal411.

When the minimal signal difference value701is higher than the preset threshold value431, the selection signal432outputted from the determining unit43is “0”, and the selecting unit50output the digital signal102; when the minimal signal difference value701is lower than or equal to the preset threshold value431, the determining unit43outputs the filter ID code703as the selection signal432, so that the selecting unit50outputs one of the first filtered signal611, the second filtered signal621, the third filtered signal631, and the fourth filtered signal641.

The present invention disclosed herein has been described by means of specific embodiments. However, numerous modifications, variations and enhancements can be made thereto by those skilled in the art without departing from the spirit and scope of the present invention set forth in the claims.