A Sub-band Aliasing Sampling Reconstruction Method Based on Frequency Interleaved Sampling Technology

Abstract

The invention discloses a sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology. An input signal enters M channels simultaneously through a power divider, and a sinusoidal signal of a suitable frequency is selected for modulation, so that the input signal of each channel generates aliasing to different degrees, and then the high-frequency part after aliasing is filtered out by a low-pass filter, so as to realize the process of sub-band decomposition; the filtered signal is sampled by an analog-to-digital converter and converted into a digital signal, and the sampling rate is increased by upsampling and digital filtering, and then converted to the frequency domain by Fourier transform for digital processing; the spectrum of each sub-band is separated by digital signal processing methods such as multiplication, spectrum mirroring and spectrum subtraction, and then the high-frequency sub-band except the baseband is moved to its original position by a digital up-conversion method, and then all sub-bands are added, and the original signal is restored by inverse Fourier transform.

Description

Technical Field

[0001] The present invention belongs to the technical field of digital signal processing, and more specifically, relates to a sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology. Background Art

[0002] With the rapid development of science and technology, the transmission rate of modern electronic signals has entered the field of tens of G or even hundreds of G. In order to capture and observe high-speed signals in real time, high-performance digitizers have become crucial measuring equipment. However, the sampling rate and analog input bandwidth of the analog-to-digital converter, the core component of the digitizer, often cannot meet the actual acquisition needs, becoming a bottleneck hindering the development of high-speed data acquisition systems. For this reason, many parallel acquisition schemes, such as time interleaved sampling technology and frequency interleaved sampling technology, have been invented to improve the performance indicators of the acquisition system. In the above parallel acquisition schemes, although the time interleaved sampling technology can increase the acquisition rate of the acquisition system exponentially with the increase in the number of channels, it cannot improve the analog input bandwidth of the system. The frequency interleaved sampling technology can increase the analog input bandwidth of the system by nearly multiples while increasing the acquisition rate of the system.

[0003] At present, many sampling architectures have been developed based on frequency interleaved sampling technology, such as digital bandwidth alternating sampling technology, frequency conversion hybrid architecture, asynchronous time interleaved sampling technology, etc. All of them use the sub-band decomposition characteristics of frequency interleaved sampling technology to reduce the input signal bandwidth of a single channel through mixing modulation to meet the needs of improving system performance. The difference lies in the difference between the mixing method and the digital signal processing method. Digital bandwidth alternating sampling technology uses a group of analog analysis filter groups to decompose the input signal into sub-bands. The large and expensive analog analysis filter group has become a bottleneck restricting its development; the frequency conversion hybrid architecture uses a group of orthogonal signals to decompose the input signal into sub-bands, but this inevitably introduces orthogonal mirror errors; asynchronous time interleaved sampling technology uses a group of pulse signals to modulate the input signal. This structure has extremely strict requirements on pulse signals and is not easy to expand. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, reduce the complexity of the analog front end for sub-band decomposition circuits, provide a sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology, and based on the principle of sub-band decomposition, improve the sampling rate and input bandwidth of the acquisition system.

[0005] To achieve the above-mentioned object of the invention, the present invention provides a sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology, characterized in that it includes the following steps:

[0006] (1) Sinusoidal signal modulation and sub-band aliasing;

[0007] (1.1) For an M-channel sub-band aliasing sampling architecture, the analog input signal is sent to M channels simultaneously through the power divider; the maximum bandwidth of the input signal is M×B, where M is the number of channels and B is the bandwidth of each sub-band after sub-band decomposition;

[0008] (1.2) In each channel, the input signal is first input to the mixer, and the mixer uses the sinusoidal signal as the local oscillator signal to mix and modulate the input signal to obtain the modulated signal of each channel; the frequency of the local oscillator signal of each channel is f k =(k-1)×B, k is the channel number, k=1,2,…,M;

[0009] (2) Analog low-pass filtering and signal acquisition;

[0010] The modulated signal of each channel passes through an analog low-pass filter with a cutoff frequency of B to filter out the high-frequency part of the signal and only retain the signal spectrum of the baseband part. Among them, the signal spectrum of the first channel is only the spectrum of the first sub-band, and the signal spectrum of each of the remaining channels is the aliasing of the current sub-band and the previous sub-band; the filtered modulated signal is then sent to the ADC for sampling to obtain the sampled digital signal of each channel;

[0011] (3) Sampling digital signal processing and signal reconstruction

[0012] (3.1) The sampled digital signal of each channel is first upsampled, then passed through a digital low-pass filter to eliminate the image spectrum introduced by upsampling, and then subjected to Fourier transform to obtain the signal spectrum of M channels;

[0013] (3.2), let the signal spectrum of the first channel be X1(f) = U1(f), and the signal spectrum of each of the remaining channels be X k (f) = U (k-1)N (f)+U kP (f), where U kP (f) represents the spectrum of the kth subband, U (k-1)N (f) represents the mirror image of the k-1th sub-band spectrum;

[0014] Subtract the spectrum of the first channel from the spectrum of the second channel to obtain the signal spectrum of the second sub-band. Similarly, traverse each sub-band and subtract the spectrum of the k-1th sub-band from the spectrum of the kth channel to obtain the signal spectrum of all sub-bands.

[0015] (3.3) Except for the signal spectrum of the first sub-band, the signal spectrum of the remaining sub-bands is digitally up-converted, and then the signal spectrum of each sub-band is digitally filtered to filter out the image spectrum;

[0016] (3.4) All sub-band spectra are added together to obtain the spectrum of the reconstructed input signal, and then the spectrum is inversely discrete Fourier transformed to restore the original input signal.

[0017] The object of the invention of the present invention is achieved in this way:

[0018] The present invention is based on a sub-band aliasing sampling reconstruction method of frequency interleaved sampling technology. The input signal enters M channels simultaneously through a power divider, and modulates by selecting a sinusoidal signal of a suitable frequency so that the input signal of each channel produces aliasing to varying degrees, and then the high-frequency part after aliasing is filtered out by a low-pass filter, so as to realize the process of sub-band decomposition; the filtered signal is sampled by an analog-to-digital converter and converted into a digital signal, and the sampling rate is increased by upsampling and digital filtering, and then converted to the frequency domain by Fourier transform for digital processing; the spectrum of each sub-band is separated by digital signal processing methods such as multiplication, spectrum mirroring and spectrum subtraction, and then the high-frequency sub-band except the baseband is moved to its original position by a digital up-conversion method, and then all sub-bands are added, and the original signal is restored by inverse Fourier transform.

[0019] At the same time, the sub-band aliasing sampling reconstruction method based on the frequency interleaved sampling technology of the present invention also has the following advantages:

[0020] Beneficial effects:

[0021] (1) Based on the sub-band decomposition characteristics of frequency interleaved sampling technology, a sub-band aliasing sampling reconstruction method is proposed. This method can double the sampling rate of the high-speed acquisition system while doubling the input bandwidth index of the high-speed acquisition system.

[0022] (2) According to the characteristics of sinusoidal signal modulation, different channels are modulated and mixed using sinusoidal signals of different frequencies, and then the sub-band decomposition is achieved through the same low-pass filter without the need for an additional analog analysis filter group. This reduces the complexity of the analog front-end hardware circuit design while achieving high performance indicators.

[0023] (3) The relationship between the digital signals sampled in each channel in the frequency domain is analyzed. The spectrum of the original signal can be restored through digital processing methods such as upsampling, multiplication, mirroring, subtraction and up-conversion, without the need for complex processing, thus reducing the complexity of signal processing at the digital end. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of sub-band aliasing sampling reconstruction based on frequency interleaved sampling technology of the present invention;

[0025] Figure 2 It is a schematic diagram of spectrum analysis of each channel in the sub-band aliasing sampling architecture;

[0026] Figure 3 It is the digital signal processing principle diagram of each channel in the sub-band aliasing sampling architecture;

[0027] Figure 4 This is the signal reconstruction result based on the sub-band aliasing sampling architecture. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0029] Example

[0030] In this embodiment, if Figure 1 As shown, the present invention provides a sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology, comprising the following steps:

[0031] S1, sinusoidal signal modulation and sub-band aliasing;

[0032] S1.1. For an M-channel sub-band aliasing sampling architecture, the analog input signal is sent to M channels simultaneously through the power divider; wherein the maximum bandwidth of the input signal is M×B, where M is the number of channels and B is the bandwidth of each sub-band after sub-band decomposition;

[0033] S1.2, In each channel, the input signal is first input to the mixer, such as Figure 2 As shown, in the mixer, a sinusoidal signal of a suitable frequency is used as the local oscillator signal to mix and modulate the input signal to obtain a modulated signal for each channel; the frequency of the local oscillator signal of each channel is f k =(k-1)×B, k is the channel number, k=1,2,…,M;

[0034] In this embodiment, according to the modulation characteristics of the sinusoidal signal, the spectrum of the analog input signal is shifted to both sides, and the shift step is the size of the carrier frequency. After the spectrum shift, the signal spectrum of each channel is an interlaced aliasing of the original input signal spectrum, and the spectrum of each sub-band can be restored in subsequent calculations. It is particularly noted that the input signal of the first channel does not need to be modulated, so there is no shifting and aliasing in the analog signal spectrum of the first channel.

[0035] S2, analog low-pass filtering and signal acquisition;

[0036] The modulated signal of each channel passes through an analog low-pass filter with a cutoff frequency of B to filter out the high-frequency part of the signal and only retain the signal spectrum of the baseband part, such as Figure 2As shown on the right, the signal spectrum of the first channel is only the spectrum of the first sub-band, and the signal spectrum of the kth (k ≥ 2)th channel is the aliasing of the spectrum mirror images of the kth sub-band and the k-1th sub-band; the filtered modulated signal is then sent to the ADC for sampling to obtain the sampled digital signal of each channel;

[0037] In this embodiment, the spectrum of the input signal is assumed to be Then the spectrum of each channel after filtering by the analog low-pass filter is expressed as:

[0038]

[0039] Where, Ω represents the simulated angular frequency, Ω k It represents the step of each channel moving in the frequency domain after modulation, X(jΩ) represents the original signal spectrum, and H(jΩ) represents the frequency response of the low-pass filter.

[0040] In this embodiment, the low-pass filter performance indicators of each channel in the sub-band aliasing sampling architecture are the same, thus greatly reducing the difficulty of designing the analog channel. At this time, the signal spectrum of each channel is the aliasing of the current sub-band and the previous sub-band. Among them, the signal spectrum of the first channel is only the spectrum part of the first sub-band, and no aliasing is generated. The filtered signal is sent to the ADC for sampling. Under ideal conditions, the acquisition rate of the ADC of each channel is twice the size of the analog low-pass filter cutoff frequency.

[0041] S3, Sampling Digital Signal Processing and Signal Reconstruction

[0042] S3.1, if Figure 3 As shown in the figure, the sampled digital signal of each channel is first upsampled to meet the sampling rate requirements of the system; upsampling will introduce a mirror spectrum while increasing the sampling rate of the sampled signal of each channel. In addition, after upsampling, the sub-band spectrum of the digital signal will be extended to the entire signal bandwidth, and aliasing components will inevitably be generated in subsequent calculations. Therefore, a digital low-pass filter is used to eliminate the mirror spectrum introduced by upsampling, and then the signal spectrum of M channels is obtained through Fourier transform;

[0043] S3.2. Since the signal spectrum of the first channel is only the spectrum of the first sub-band, no aliasing occurs, which is recorded as X1(f) = U1(f). The signal spectrum of each of the remaining channels is X k (f) = U (k-1)N (f)+U kP (f), where U kP (f) represents the spectrum of the kth subband, U (k-1)N (f) represents the mirror image of the k-1th sub-band spectrum;

[0044] It should be noted that due to the modulation characteristics of the sinusoidal signal, the signal spectrum is processed and moved to both sides, and the amplitude is also halved. Therefore, before calculation, all channel spectra except the first channel spectrum need to be multiplied by 2 to restore the original amplitude.

[0045] The spectrum of the first channel is the spectrum of the first sub-band. The spectrum of the second channel is subtracted from the mirror image of the first channel spectrum to obtain the signal spectrum of the second sub-band. Similarly, traverse each sub-band and subtract the mirror image of the k-1th sub-band spectrum from the spectrum of the kth (k≥2)th channel to obtain the spectrum of the kth sub-band. In this way, the signal spectrum of all sub-bands can be obtained.

[0046]

[0047] Among them, fliplr represents the mirror calculation, and ω is the digital angular frequency.

[0048] S3.3. Except for the signal spectrum of the first sub-band, the signal spectrum of the remaining sub-bands is digitally up-converted and the signal spectrum is moved back to its high-frequency part. Since the up-conversion will also introduce the image spectrum, we digitally filter the signal spectrum of each sub-band again to filter out the image spectrum. Finally, the spectrum of each channel is obtained as follows:

[0049]

[0050] Among them, ω k represents the step of spectrum shifting when the kth channel is up-converted, Y k (e jω ) represents the spectrum of each channel after digital processing, G k (e jω ) represents the frequency response of the digital filter.

[0051] S3.4. Add all sub-band spectra to obtain the spectrum Y(e) of the reconstructed input signal. jω ), and then perform inverse discrete Fourier transform on the spectrum to restore the original input signal;

[0052]

[0053] Example Simulation

[0054] In this embodiment, a four-channel sub-band aliasing acquisition system is simulated, the total bandwidth of the simulated input signal is 200MHz, the input signal is divided into 4 sub-bands, and the bandwidth of each sub-band is 50MHz. A multi-tone signal and a broadband signal are selected as test signals. Figure 4As shown on the right, the frequencies of the multi-tone signals are located in each sub-band, which are 45, 90, 135, and 180 MHz, and the frequency amplitudes are 1, 0.7, 0.5, and 0.3, respectively. Figure 4 The upper right side is the original spectrum of the input signal, and the lower side is the spectrum restored by the present invention. According to the comparison, it can be seen that the present invention can restore the original spectrum of the multi-tone signal without distortion; Figure 4 As shown on the left, the frequency band of the broadband signal is located at the overlap of every two sub-bands, and the broadband size is 10MHz. The carrier frequencies of the modulation signals of the second to fourth channels are 50, 100, and 150MHz respectively; the cutoff frequency of the analog low-pass filter is 50MHz, and the acquisition rate of the ADC is 100MSPS. Figure 4 The upper left side is the original spectrum of the input signal, and the lower side is the spectrum restored by the present invention. From the comparison, it can be seen that the present invention can restore the original spectrum of the broadband signal without distortion. Finally, the total sampling rate of the system is 400MSPS. Compared with a single ADC, the signal input bandwidth and sampling rate are both increased by 4 times.

[0055] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology, characterized in that: The following steps are involved: (1) Sinusoidal signal modulation and sub-band aliasing; (1.1) For an M-channel sub-band aliasing sampling architecture, the analog input signal is sent to M channels simultaneously through the power divider; the maximum bandwidth of the input signal is M×B, where M is the number of channels and B is the bandwidth of each sub-band after sub-band decomposition; (1.2) In each channel, the input signal is first input to the mixer, and the mixer uses the sinusoidal signal as the local oscillator signal to mix and modulate the input signal to obtain the modulated signal of each channel; the frequency of the local oscillator signal of each channel is f k =(k-1)×B, k is the channel number, k=1,2,…,M; (2) Analog low-pass filtering and signal acquisition; The modulated signal of each channel passes through an analog low-pass filter with a cutoff frequency of B to filter out the high-frequency part of the signal and only retain the signal spectrum of the baseband part. Among them, the signal spectrum of the first channel is only the spectrum of the first sub-band, and the signal spectrum of each of the remaining channels is the aliasing of the current sub-band and the previous sub-band; the filtered modulated signal is then sent to the ADC for sampling to obtain the sampled digital signal of each channel; (3) Sampling digital signal processing and signal reconstruction (3.1) The sampled digital signal of each channel is first upsampled, then passed through a digital low-pass filter to eliminate the image spectrum introduced by upsampling, and then subjected to Fourier transform to obtain the signal spectrum of M channels; (3.2), let the signal spectrum of the first channel be X1(f) = U1(f), and the signal spectrum of each of the remaining channels be X k (f) = U (k-1)N (f)+U kP (f), where U kP (f) represents the spectrum of the kth subband, U (k-1)N (f) represents the mirror image of the k-1th sub-band spectrum; Subtract the spectrum of the first channel from the spectrum of the second channel to obtain the signal spectrum of the second sub-band. Similarly, traverse each sub-band and subtract the spectrum of the k-1th sub-band from the spectrum of the kth channel to obtain the signal spectrum of all sub-bands. (3.3) Except for the signal spectrum of the first sub-band, the signal spectrum of the remaining sub-bands is digitally up-converted, and then the signal spectrum of each sub-band is digitally filtered to filter out the image spectrum; (3.4) All sub-band spectra are added together to obtain the spectrum of the reconstructed input signal, and then the spectrum is inversely discrete Fourier transformed to restore the original input signal.

2. The sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology according to claim 1 is characterized in that: The performance index of the analog low-pass filter of each channel in the sub-band aliasing sampling architecture is the same.

3. The sub-band aliasing sampling reconstruction method based on frequency interleaved sampling technology according to claim 1, characterized in that: The acquisition rate of the ADC of each channel in the sub-band aliasing sampling architecture is twice the cut-off frequency of the analog low-pass filter.

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