CN118249830A

CN118249830A - Method for demodulating RF signals

Info

Publication number: CN118249830A
Application number: CN202311781795.XA
Authority: CN
Inventors: F·斯特勒; P·古亚德
Original assignee: STMicroelectronics Grand Ouest SAS
Current assignee: STMicroelectronics Grand Ouest SAS
Priority date: 2022-12-22
Filing date: 2023-12-22
Publication date: 2024-06-25

Abstract

The present disclosure relates to a method for demodulating an RF signal, the method comprising the steps of: detecting whether an analog-to-digital converter (ADC) of a Near Zero Intermediate Frequency (NZIF) receiver is in a clip state; and IF so, determining and storing a first value (RSSI 1) representative of the energy of the received signal demodulated by the Near Zero Intermediate Frequency (NZIF) receiver using the first intermediate frequency (IF 1); a second value (RSSI 2) is determined and stored, the second value representing the energy of the received signal demodulated by the Near Zero Intermediate Frequency (NZIF) receiver using a second intermediate frequency (IF 2) corresponding to the opposite value (IF 1) of the first intermediate frequency (IF 1), the intermediate frequency corresponding to the minimum of said first and second values being selected.

Description

Method for demodulating RF signals

Cross Reference to Related Applications

The present application claims the benefit of priority from french patent application number EP22306990 entitled "Method for demodulating A RF SIGNAL (method for demodulating RF signals)" filed on month 22 of 2022, which is incorporated herein by reference to the maximum extent allowed by law.

Technical Field

The present disclosure relates generally to methods for demodulating RF signals and RF circuits for implementing such methods.

Background

Radio Frequency (RF) receivers can be divided into two broad categories: zero Intermediate Frequency (ZIF) architecture based receiver and Near Zero Intermediate Frequency (NZIF) architecture based receiver.

The NZIF receiver converts the received radio signal to an intermediate frequency, the carrier frequency of which is in the order of the baseband signal bandwidth, but significantly lower than the radio carrier frequency to be demodulated.

The NZIF receiver may fail in the presence of blockers or adjacent channels near the frequency of the received signal and with stronger strength than the signal of interest.

Disclosure of Invention

It is desirable to provide a method for demodulating an RF received signal that allows the receiver to behave correctly in the presence of blockers or adjacent channels.

One or more embodiments address all or part of the disadvantages of known methods for demodulating RF received signals.

One or more embodiments provide a method for demodulating an RF signal, the method comprising the steps of: detecting whether an analog-to-digital converter of the near-zero intermediate frequency receiver is in a clipping (clipping) state; and if so, determining and storing a first value representing the energy of the received signal demodulated by the near zero intermediate frequency receiver using the first intermediate frequency; a second value is determined and stored, the second value representing the energy of the received signal demodulated by the near zero intermediate frequency receiver using a second intermediate frequency corresponding to an opposite value of the first intermediate frequency, and an intermediate frequency corresponding to a minimum of the first and second values is selected.

One embodiment provides an RF circuit configured to: detecting whether an analog-to-digital converter of the near-zero intermediate frequency receiver is in a clipping state; and if so, determining and storing a first value representing the energy of the received signal demodulated by the near zero intermediate frequency receiver using the first intermediate frequency; a second value is determined and stored, the second value representing the energy of the received signal demodulated by the near zero intermediate frequency receiver using a second intermediate frequency corresponding to an opposite value of the first intermediate frequency, the intermediate frequency corresponding to the minimum of the first and second values being selected.

According to one embodiment, the selected intermediate frequency is also used by the near zero intermediate frequency receiver to demodulate the next frame of the received signal.

According to one embodiment, if the analog-to-digital converter of the near zero intermediate frequency receiver is not in a clipping state, the current intermediate frequency is maintained.

According to one embodiment, the clipping state is detected when a given number of samples of the analog-to-digital converter is equal to a maximum or minimum value of the analog-to-digital converter.

According to one embodiment, clipping state detection is performed for each frame of the received signal.

According to one embodiment, clip state detection is performed at the end of each frame.

According to one embodiment, the first energy indication and the second energy indication are wideband received signal strength indications.

According to one embodiment, a method or circuit includes: the received signal is filtered using an analog low pass filter and the bandwidth of the wideband received signal strength indication is defined by the bandwidth of the analog low pass filter.

According to one embodiment, a method or circuit includes: the RF signal is amplified and the amplified signal is split into a first path and a second path.

According to one embodiment, a method or circuit includes: the amplified RF signal is mixed in a first path with an in-phase signal of a local oscillator frequency corresponding to a sum of a center frequency of the received signal and the selected intermediate frequency, and the amplified RF signal is mixed in a second path with a quadrature signal of the local oscillator frequency.

According to one embodiment, the analog low pass filter bandwidth is centered around the local oscillator frequency.

According to one embodiment, a method or circuit includes: filtering the high frequency of the mixed signal of the first path and the high frequency of the mixed signal of the second path; amplifying the filtered signal; and converting the amplified and filtered signal into a digital signal using an analog-to-digital converter.

According to one embodiment, a method or circuit includes: the digital signal is mixed with a third signal having the selected intermediate frequency.

According to one embodiment, the first energy indication and the second energy indication correspond to square roots of a sum of squares of the first path signal and squares of the orthogonal path signal.

According to one embodiment, the first energy indication and the second energy indication are determined after analog-to-digital conversion by the analog-to-digital converter and before digital mixing.

Drawings

The above features and advantages and other features and advantages will be described in detail in the following description of particular embodiments, given by way of example and not limitation with reference to the accompanying drawings, in which:

FIG. 1 illustrates an embodiment of an RF circuit;

fig. 2 illustrates an embodiment of an RF signal demodulation method;

Fig. 3 illustrates steps of the method of fig. 2 in the presence of adjacent channels;

fig. 4 illustrates steps of the method of fig. 2 in the presence of adjacent channels;

FIG. 5 illustrates steps of the method of FIG. 2 in the presence of a blocker; and

Fig. 6 illustrates the steps of the method of fig. 2 in the presence of a blocker.

Detailed Description

Like features have been designated by like reference numerals throughout the various drawings. In particular, structural and/or functional features common between the various embodiments may have the same reference numerals and may be provided with the same structure, dimensions, and material properties.

For clarity, only the operations and elements useful for understanding the embodiments described herein have been illustrated and described in detail.

Unless otherwise indicated, when referring to two elements being connected together, this means that there is no direct connection of any intermediate element other than a conductor, and when referring to two elements being coupled together, this means that the two elements may be connected or they may be coupled via one or more other elements.

In the following disclosure, unless otherwise indicated, when reference is made to absolute positional qualifiers such as the terms "front", "rear", "top", "bottom", "left", "right", etc., or relative positional qualifiers such as the terms "above", "below", "higher", "lower", etc., or orientation qualifiers such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures.

Unless otherwise indicated, the expressions "about", "approximately" and "on the order of …" mean within 10%, and preferably within 5%.

In one or more embodiments, the method and the NZIF-based circuit are implemented hereinafter to detect whether the presence of a normalized blocker or an adjacent channel induces an unwanted signal in an RF NZIF-based circuit receiver. In one or more embodiments, in the event that the presence of an undesired signal is detected, the intermediate frequency is adapted according to the channel energy indication to eliminate the undesired signal.

Fig. 1 illustrates an embodiment of an RF circuit 100. More precisely, fig. 1 illustrates an RF transceiver architecture.

The RF circuit 100 includes, for example, an NZIF receiver 101.

In the illustrated example, the NZIF receiver 101 comprises a first module RXFE (receive front end), the first module RXFE being coupled or preferably connected to a second module BB (baseband). In one or more embodiments, the second module BB is coupled or preferably connected to a third module ADC (analog-to-digital converter), which is coupled or preferably connected to a fourth module DFE (digital front end).

In one or more embodiments, the illustrated NZIF receiver includes an analog RF filter 104, the analog RF filter 104 being, for example, a bandpass filter configured to filter a received signal, the received signal including a frequency band having a center frequency Frx.

In one or more embodiments, the first module RXFE includes an amplifier 106, such as a Low Noise Amplifier (LNA), the amplifier 106 being configured to amplify the received RF signal filtered by the analog RF filter 104. In one or more embodiments, the amplified signal is then split into two different paths 111, 113. In one or more embodiments, the first module includes one mixer 114, 116 for each path. In one or more embodiments, each of the mixers 114, 116 is configured to mix the received RF signal Frx of the corresponding path with a signal having a local oscillator frequency LO. In the disclosed embodiment, the frequency LO corresponds to the sum of the center frequency Frx of the received signal and the intermediate frequency IF1 or IF2, and is determined from the value RSSI1 or RSSI2, which represents the energy of the received signal demodulated by the Near Zero Intermediate Frequency (NZIF) receiver 101. In one or more embodiments, the local oscillator frequency LO of path 111 corresponds to the in-phase signal LO-I and the local oscillator frequency LO of path 113 corresponds to the quadrature signal LO-Q. In one or more embodiments, the in-phase LO-I signal and the quadrature LO-Q signal are the real and imaginary parts, respectively, of a signal having a frequency LO and supplied by the local oscillator 103.

In one or more embodiments, frequency downconversion is implemented by mixers 114 and 116, respectively. In one or more embodiments, the in-phase and quadrature mixed signal frequencies at the outputs of mixers 114 and 116, respectively, may take two discrete values IF1 or IF2.

In one or more embodiments, the mixing signals at the outputs of the mixers 114, 116 are coupled or preferably connected, respectively, to low-pass analog baseband filters 117, 126 of the second module BB, which are configured to filter out frequencies that are two or three times higher than, for example, the intermediate frequency, e.g., 1.5MHz for an intermediate frequency of 480 kHz. In one or more embodiments, the low pass filters 117, 126 are equivalent to band pass filters centered around the local oscillator frequency LO when converted to RF. In other words, in one or more embodiments, signals outside of the band lo±baseband BB bandwidth are rejected by the filters 117, 126.

In one or more embodiments, the outputs of the filters 117, 126 are coupled or preferably connected to different series of amplifiers (118, 120, 122 for the first path 111 and 128, 130, 132 for the second path 113), respectively, the amplifiers being programmable gain amplifiers of the second module BB, for example. The number of amplifiers may depend on the application.

In one or more embodiments, the outputs of the amplifiers 122 and 132 are coupled or preferably connected, respectively, to different analog-to-digital converters (ADCs) 133, 134 of the third module, the analog-to-digital converters 133, 134 being used to convert the filtered and amplified signals of the second module into digital signals.

In one or more embodiments, the fourth module DFE includes an optional Direct Current (DC) offset cancellation circuit not shown, thereby coupling the output of the analog-to-digital converter 133 to the mixer 140 for the first path 111 and the analog-to-digital converter 134 to the further mixer 146 for the second path 113. In one or more embodiments, the DC offset cancellation circuit is configured to cancel unwanted DC biases that may originate from the received signal Frx or from the ADC circuit, thereby improving system performance degradation and bit error rate.

In the example shown, an oscillator 143 (NCO) of the fourth module DFE, which is for example a digitally controlled oscillator, supplies a signal nco_if with the determined intermediate frequency IF1 or IF2 to the mixers 140, 146.

In one or more embodiments, de-rotation is implemented by the mixers 140, 146 for the first path signal and the second path signal, respectively.

In one or more embodiments, a low pass filter 142 (LPF) of the first path couples the output of the mixer 140 to a first decimator 144 (decimator)Select 8) and a further low pass filter 148 (LPF) of the second path couples the output of the mixer 146 to a second decimator 149 (decimator/>Selection 8). In one or more embodiments, the decimator is configured to reduce the data rate by removing samples from the data stream without affecting the signal. In the illustrated example, the decimator is configured as an eighth decimator. Other configurations are also possible, such as one-half decimation. The half decimation function is equivalent to a clocked (clocked) data converter at half the original rate, with the analog anti-aliasing filter at half the original nyquist bandwidth. In one or more embodiments, the decimation filter eliminates unwanted signal images. In one or more embodiments, it also eliminates half of the noise power. In one or more embodiments, the overall signal-to-noise ratio (SNR) improves because the desired signal remains unchanged and the noise power is reduced by half. In one or more embodiments, the SNR improves by 10 x log (D) for any decimation factor D.

In one or more embodiments, the outputs of decimators 144 and 149 are coupled or preferably connected to digital channel filters 160, 162, respectively, digital channel filters 160, 162 being, for example, bandpass filters having a bandwidth slightly greater than the bandwidth of the frequency band of the received signal. In an example not shown, digital channel filters 160, 162 couple the low path filters 142, 148 to respective decimators 144, 149.

In one or more embodiments, the outputs of the digital-to-analog filters 160, 162 are coupled or preferably connected to Digital Signal Processor (DSP) inputs 180 (I path) and 182 (Q path) to analyze the demodulated received signal. In an example not shown, digital Signal Processor (DSP) inputs 180 (I path) and 182 (Q path) couple the digital channel filters 160, 162 to the respective decimators 144, 149.

In one or more embodiments, the computation circuit 170 of the RF circuit 100 is coupled or preferably connected to the outputs of the analog-to-digital converters 133 and 134, for example.

In one or more embodiments, the calculation circuit 170 is configured to detect whether the analog-to-digital converter 133, 134 of at least one of the paths 111, 113 is in a clipped state.

In one or more embodiments, the computing circuit 170 is further configured to determine and store values RSSI1, RSSI2, for example, the values RSSI1, RSSI2 representing the energy of the received signal after demodulation or partial demodulation. In one or more embodiments, the value RSSI1 represents the energy of the received signal when the first intermediate frequency IF1 is used for demodulation by the NZIF receiver, and the value RSSI2 represents the energy of the received signal when the second intermediate frequency IF2 is used.

In one or more embodiments, the first energy indication RSSI1 and the second energy indication RSSI2 are, for example, received Signal Strength Indications (RSSI), such as wideband received signal strength indications. In other words, in one or more embodiments, the first energy-indicative RSSI1 and the second energy-indicative RSSI2 correspond to, for example, RSSI within the bandwidth of the low-pass analog filters 117, 126.

In another example, the first energy-indicative RSSI1 and the second energy-indicative RSSI2 correspond to square roots of a sum of squares of the first path signal and squares of the orthogonal path signal.

In one or more embodiments, the calculation circuit 170 is configured to adapt the intermediate frequency of the NZIF receiver 101 according to the clipping state of the ADC circuits 133 and/or 134 and according to the received signal strength indication RSSI1, RSSI 2.

Fig. 2 illustrates an embodiment of an RF signal demodulation method. In one example, the demodulation method may be implemented by the RF circuit of fig. 1.

More specifically, fig. 2 illustrates the steps of a method for selecting an intermediate frequency IF to be used for demodulation.

In step 202 (IF selection algorithm entry), the demodulation method begins.

In a next step 204 (ADC clipping. In one or more embodiments, the clipping condition is detected, for example, when a given number of samples of the analog-to-digital converters 133, 134 is equal to a maximum or minimum value of the analog-to-digital converter 134. In the example of an 8-bit ADC, the minimum value is-128 and the maximum value is +127. In one or more embodiments, clip state detection is performed, for example, for each frame of the received signal and/or at the end of each frame.

In one or more embodiments, if the ADC is not in a clip state ("no" output of block 204), the intermediate frequency is not modified and remains the same as the previous frame. In one or more embodiments, the method of selecting the intermediate frequency ends (step 218—exit IF selection).

In one or more embodiments, if the ADC is in a clip state (output yes of block 204), step 206 (RSSI 1=rssi@if1) is performed. In step 206, a first value RSSI1 representative of the energy of the received signal demodulated by the NZIF receiver using the first intermediate frequency IF1 is determined and stored. In one or more embodiments, the value IF1 is the current intermediate frequency of, for example, an NZIF receiver. In an example of an application of the narrowband internet of things (NBIOT), the value IF1 is set to 480kHz, for example. In one or more embodiments, step 206 is performed, for example, by computing circuitry 170.

In a next step 208 (inverting the RX IF), the intermediate frequency is inverted. In other words, for example, the intermediate frequency IF2 is set to the opposite value of IF1 (e.g., -480 kHz).

In a next step 210 (RSSI 2=rssi@if2), a second value RSSI2 representing the energy of the received signal demodulated by the NZIF receiver with the opposite intermediate frequency IF2 is determined and stored. Step 210 is performed, for example, by the computing circuitry 170.

In a next step 212 (RSSI 1< RSSI 2. In one or more embodiments, IF the first value RSSI1 is less than the second value (branch yes), step 216 (if=if1) is performed. In one or more embodiments, IF the first value RSSI1 is greater than the second value (branch no), step 214 (if=if2) is performed.

In step 214, the intermediate frequency is set to a second intermediate frequency IF2.

In step 216, the intermediate frequency is set to a first intermediate frequency IF1.

After step 214 or 216, the selection method is ended by step 218.

The method of fig. 2 allows for example to select intermediate frequency values that can reduce the wideband energy of the channel, thereby reflecting the fact that unwanted signals are not superimposed to the signal of interest.

Fig. 3 illustrates the steps of the method of fig. 2 in the presence of adjacent channels. Fig. 3 uses an example of NBIOT signals. The method may be applied to other signal frequencies. More specifically, in one or more embodiments, the steps of fig. 3 illustrate a case where there is an adjacent channel 310 (adjacent channel) with a frequency that spans the local oscillator frequency LO, and results in a case where the ADC is in a clipped state and RSSI1 is greater than RSSI 2.

In step A1), the intermediate frequency IF1 is set and a first analog down-conversion is applied to the received signal by mixing the received signal with a signal having a local oscillator frequency LO. In one or more embodiments, the frequency LO is set equal to the intermediate frequency IF1 plus the receive signal center frequency Frx. In the example of fig. 3, the adjacent channel 310 is on the opposite side of the desired signal as compared to the local oscillator frequency LO. In one or more embodiments, at the end of step A1), the center frequency of the signal is shifted from the frequency LO by an intermediate frequency IF1.

In step B1), the signal obtained at the end of step A1) is digitally processed to be de-rotated by means of the intermediate frequency IF1, thereby down-converting the signal to baseband. In one or more embodiments, during step B1), the filtered portion of the adjacent channel 310 undergoes image rejection, but the image of the filtered adjacent channel 320 remains present and forms a band spanning the frequency LO and the channel bandwidth.

In one or more embodiments, the resulting down-converted signal is filtered by digital channel filters 160 and 162 (digital channel filters) shown in C1). In one or more embodiments, digital channel filters 160 and 162 have bandwidths centered on the baseband and extending slightly on either side of the demodulated signal. Step 206 is performed, for example, during step C1) to determine RSSI1.

In one or more embodiments, a portion of the image 320 remains within the bandwidth of the digital channel filter and may cause additional energy in the channel and ADC clipping.

Fig. 4 illustrates the steps of the method of fig. 2 in the presence of adjacent channels 310. In one or more embodiments, the adjacent channel 310 is similar to the adjacent channel of fig. 3. More precisely, in one or more embodiments, fig. 4 illustrates step 208 and step 210 of fig. 2.

In step a' 1), a first analog down-conversion is applied to the received signal by mixing the received signal with a signal having a local oscillator frequency LO. In one or more embodiments, the frequency LO is set equal to the inverted intermediate frequency IF2 plus the receive signal center frequency Frx. In one or more embodiments, since IF2 is opposite IF1, the adjacent channel is now on the same side of the LO as the desired signal, as compared to the example of fig. 3. At the end of step A1'), the center frequency of the signal is shifted from the frequency LO by the intermediate frequency IF2. In one or more embodiments, the received signal is then filtered by analog low pass filters 117, 126 (baseband filters). In the illustrated example, the bandwidth of the analog filter is twice or three times the intermediate frequency and defines a wideband RSSI measurement bandwidth (wideband RSSI). In one or more embodiments, adjacent channel portions that remain unfiltered by analog filters 117, 126 are now outside of the received signal.

In step B '1), the signal obtained at the end of step A1') is digitally processed to perform another de-rotation using the inverted intermediate frequency IF2, thereby down-converting the signal to baseband. In one or more embodiments, during step B1'), the filtered portion of the adjacent channel 310 undergoes image rejection, but the filtered image 420 of the adjacent channel remains present and forms a frequency band that extends outside the channel bandwidth.

In one or more embodiments, the resulting down-converted signal is filtered by digital channel filters 160 and 162 (digital channel filters) shown in C1'). In one or more embodiments, digital channel filters 160 and 162 have bandwidths centered on the baseband and extending slightly on either side of the demodulated signal. Step 210 is performed, for example, during step C1') to determine RSSI2.

In one or more embodiments, the image 420 and the unfiltered portion of the adjacent channel are outside the bandwidth of the digital channel filter. They do not add additional energy to the channel because it can be measured by wideband RSSI, thus preventing ADC clipping.

Fig. 5 illustrates the steps of the method of fig. 2 in the presence of a blocker. The example of fig. 5 is similar to the example of fig. 3, except that adjacent channels are replaced by blockers 510 (blockers), the blockers 510 having frequencies that lie within the bandwidth of the analog filter 104 on the low frequency side.

In step A2), the intermediate frequency IF1 is set and a first analog de-rotation is applied to the received signal by mixing the received signal with a signal having a local oscillator frequency LO. In one or more embodiments, the frequency LO is set equal to the intermediate frequency IF1 plus the receive signal center frequency Frx. In the example of fig. 5, blocker 510 is located on the opposite side of the desired signal as compared to the local oscillator frequency LO. In one or more embodiments, at the end of step A2), the center frequency of the signal is shifted from the frequency LO by an intermediate frequency IF1. In one or more embodiments, the received signal is then filtered by analog low pass filters 117, 126 (baseband filters). In the illustrated example, the bandwidth of the analog filter is twice or three times the intermediate frequency and defines a wideband RSSI measurement bandwidth (wideband RSSI).

In step B2), the signal obtained at the end of step A2) is digitally processed to be de-rotated by means of the intermediate frequency IF1, thereby down-converting the signal to baseband. In one or more embodiments, during step B2), the filtered portion of blocker 510 undergoes image rejection, but image 520 of the filtered blocker remains present and has an image frequency that falls within the channel bandwidth.

In one or more embodiments, the resulting down-converted signal is filtered by digital channel filters 160 and 162 (digital channel filters) shown in C2), and even if the blocker frequencies are filtered by the digital filters, a portion of image 520 still exists within the bandwidth of the digital channel filters and may cause additional energy in the channel and cause ADC clipping.

Step 206 is performed, for example, during step C2) to determine RSSI1.

Fig. 6 illustrates the steps of the method of fig. 2 in the presence of a blocker 510.

In step A2'), a first analog down-conversion is applied to the received signal by mixing the received signal with a signal having a local oscillator frequency LO. In one or more embodiments, the frequency LO is set equal to the inverted intermediate frequency IF2 plus the receive signal center frequency Frx. In one or more embodiments, since IF2 is opposite IF1, the blocker signal is now on the same side of the LO as the desired signal, as compared to the example of fig. 3. In one or more embodiments, at the end of step A2'), the center frequency of the signal is shifted from the frequency LO by an intermediate frequency IF2. The received signal is then filtered by analog low pass filters 117, 126 (baseband filters). In the illustrated example, the bandwidth ratio intermediate frequency of the analog filter is 2 or 3 times and defines a wideband RSSI measurement bandwidth (wideband RSSI). In one or more embodiments, adjacent channel portions that remain unfiltered by analog filters 117, 126 are now outside of the received signal.

In step B '2), the signal obtained at the end of step A2') is digitally processed to be de-rotated with the inverted intermediate frequency IF2, thereby down-converting the signal to baseband. In one or more embodiments, during step B2'), the filtered portion of blocker 520 undergoes image rejection, but the image of the filtered adjacent channel 520 is present at frequencies extending outside the channel bandwidth on the high frequency side.

In one or more embodiments, the resulting down-converted signal is filtered by digital channel filters 160 and 162 (digital channel filters) shown in C2'). In one or more embodiments, the digital channel filters 160, 162 have bandwidths centered on the baseband and extending slightly on either side of the demodulated signal.

In one or more embodiments, the image 520 and the unfiltered portion of the blocker 510 are outside the bandwidth of the digital channel filter. In one or more embodiments, they do not add additional energy in the channel because it can be measured by wideband RSSI, thus preventing ADC clipping.

Step 210 is performed, for example, during step C2') to determine RSSI2.

Fig. 3-6 illustrate that in one or more embodiments, by inverting the intermediate frequency, the effects of adjacent channels and/or blockers that might otherwise create ADC clipping (the case of fig. 3 and 5) can be prevented. In one or more embodiments, relative to the method of fig. 2, by inverting the intermediate frequency and comparing the indications of energy in wideband channels RSSI1 and RRSI2 when the ADC is clipping, it is allowed to be able to select the configuration corresponding to the case where the energy is lowest in the wideband, which will in turn result in preventing the ADC from clipping.

Various embodiments and modifications have been described. Those skilled in the art will appreciate that certain features of the embodiments can be combined and that other modifications will readily occur to those skilled in the art. In particular, even though the case where the adjacent channel and blocker exist on the low frequency side has been illustrated in fig. 3 to 6, the reverse reasoning can be implemented for the case where the adjacent channel and blocker initially exist on the high frequency side. In one or more embodiments, inverting the intermediate frequency and selecting the lowest wideband channel energy configuration may provide a solution for preventing ADC clipping and other adjacent channel/blocker effects in the case of ADC clipping.

Furthermore, in one or more embodiments, even though a solution has been described for inverting the intermediate frequency, intermediate frequency values that are close to the inverse of the initial intermediate frequency value may be used.

Finally, in one or more embodiments, practical implementations of the embodiments and variations described herein are within the ability of one skilled in the art based on the functional description provided above. In particular, in one or more embodiments, the proposed methods and circuits may be used for different RF signal bands, such as 4G, 5G, ioT or non-cellular RF standards BT, zigBee or other industry standards.

Claims

1. A method for demodulating a radio frequency, RF, signal, the method comprising:

Detecting whether an analog-to-digital converter ADC of a near-zero intermediate frequency NZIF receiver is in a clipping state or not; and

When the ADC is in the clipping state:

Determining and storing a first value representing a first energy of a received signal demodulated by the NZIF receiver using a first intermediate frequency;

determining and storing a second value representing a second energy of the received signal demodulated by the NZIF receiver using a second intermediate frequency, the second intermediate frequency corresponding to an inverse of the first intermediate frequency; and

An intermediate frequency corresponding to the minimum of the first and second values is selected from the first and second intermediate frequencies.

2. The method of claim 1, wherein the selected intermediate frequency is further used by the NZIF receiver to demodulate a next frame of the received signal.

3. The method of claim 1, wherein a current intermediate frequency is maintained when the ADC of the NZIF receiver is not in the clip state.

4. The method of claim 1, wherein the clip state is detected when a particular number of samples of the ADC is equal to a maximum or minimum value of the ADC.

5. The method of claim 1, wherein the detecting of the clipping state is performed for each frame of the received signal.

6. The method of claim 5, wherein the detecting of the clip state is performed at a respective end of each frame.

7. The method according to claim 1, wherein:

the first value and the second value are wideband received signal strength indications, and the method further comprises: the received signal is filtered with an analog low pass filter, wherein a first bandwidth of the wideband received signal strength indication is defined by a second bandwidth of the analog low pass filter.

8. The method of claim 1, further comprising:

Amplifying the RF signal;

Splitting the amplified RF signal into a first path signal for a first path and a second path signal for a second path;

Mixing the first path signal with an in-phase signal of a local oscillator frequency, which corresponds to a first sum of a center frequency of the received signal and the selected intermediate frequency, thereby obtaining a first mixed signal; and

Mixing the second path signal with a quadrature signal of the local oscillator frequency, thereby obtaining a second mixed signal,

Wherein the analog low pass filter bandwidth is centered about the local oscillator frequency.

9. The method of claim 8, further comprising:

Filtering a high frequency of the first mixing signal of the first path and a high frequency of the second mixing signal of the second path, thereby obtaining a first filtered signal corresponding to the first mixing signal and a second filtered signal corresponding to the second mixing signal;

Amplifying the first and second filtered signals, thereby obtaining a first amplified filtered signal corresponding to the first filtered signal and a second amplified filtered signal corresponding to the second filtered signal;

Converting the first amplified filtered signal and the second amplified filtered signal to digital signals using the ADC; and

The digital signal is mixed with a third signal having the selected intermediate frequency.

10. The method according to claim 8, wherein:

The first value and the second value correspond to square roots of a second sum of squares of the first path signal and squares of the second path signal, and

The first value and the second value are determined after analog-to-digital conversion by the ADC and before mixing the digital signal.

11. An apparatus for demodulating a radio frequency, RF, signal, comprising:

RF circuitry configured to:

When the ADC is in the clipping state:

12. The apparatus of claim 11, wherein the selected intermediate frequency is further used by the NZIF receiver to demodulate a next frame of the received signal.

13. The apparatus of claim 11, wherein a current intermediate frequency is maintained when the ADC of the NZIF receiver is not in the clip state.

14. The apparatus of claim 11, wherein the clip state is detected when a particular number of samples of the ADC is equal to a maximum or minimum value of the ADC.

15. The device of claim 11, wherein the detection of the clip state is performed for each frame of the received signal.

16. The device of claim 15, wherein the detection of the clip state is performed for each frame of the received signal.

17. The apparatus of claim 11, wherein:

the first value and the second value are wideband received signal strength indications, an

The RF circuit is further configured to filter the received signal with an analog low pass filter, wherein a first bandwidth of the wideband received signal strength indication is defined by a second bandwidth of the analog low pass filter.

18. An apparatus for demodulating a radio frequency, RF, signal, comprising:

RF circuitry configured to:

When the ADC is in the clipping state:

Determining and storing a second value representing a second energy of the received signal demodulated by the NZIF receiver using a second intermediate frequency, the second intermediate frequency corresponding to an inverse of the first intermediate frequency;

Selecting an intermediate frequency corresponding to a minimum value of the first and second values from the first and second intermediate frequencies;

Amplifying the RF signal; and

The amplified RF signal is split into a first path signal for a first path and a second path signal for a second path.

19. The apparatus of claim 18, wherein the RF circuit is further configured to:

Mixing the first path signal with an in-phase signal of a local oscillator frequency, which corresponds to the sum of the center frequency of the received signal and the selected intermediate frequency, thereby obtaining a first mixed signal; and

The second path signal is mixed with a quadrature signal of the local oscillator frequency, thereby obtaining a second mixed signal.

20. The device of claim 19, wherein an analog low pass filter bandwidth is centered about the local oscillator frequency.

21. The apparatus of claim 20, wherein the RF circuit is further configured to:

Amplifying the first and second filtered signals, thereby obtaining a first amplified filtered signal corresponding to the first filtered signal and a second amplified filtered signal corresponding to the second filtered signal; and

The first amplified filtered signal and the second amplified filtered signal are converted to digital signals using the ADC.

22. The apparatus of claim 21, wherein the RF circuit is further configured to mix the digital signal with a third signal having the selected intermediate frequency.

23. The apparatus of claim 18, wherein the first value and the second value correspond to square roots of a sum of squares of the first path signal and squares of the second path signal.

24. The apparatus of claim 23, wherein the first value and the second value are determined after analog-to-digital conversion by the ADC and before mixing a digital signal.