CN109981124B - Adaptive sampling method for analog-to-digital converter for improving sensitivity attenuation of radio frequency receiver - Google Patents
Adaptive sampling method for analog-to-digital converter for improving sensitivity attenuation of radio frequency receiver Download PDFInfo
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- CN109981124B CN109981124B CN201910289535.8A CN201910289535A CN109981124B CN 109981124 B CN109981124 B CN 109981124B CN 201910289535 A CN201910289535 A CN 201910289535A CN 109981124 B CN109981124 B CN 109981124B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
- H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
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Abstract
The invention relates to the technical field of radio frequency receivers, and discloses an adaptive sampling method of an analog-to-digital converter for improving the sensitivity attenuation of a radio frequency receiver, which comprises the following steps: setting the working frequency of the digital demodulator as the working frequency with optimal performance, wherein the sampling frequency of the analog-to-digital converter is equal to the frequency of the digital demodulator; in a channel which is not influenced by high-order frequency waves of the analog-to-digital converter, the sampling frequency of the analog-to-digital converter and the working frequency of the digital demodulator are fixed; switching the sampling frequency of the A/D converter and the working frequency of the digital demodulator to f in the channel affected by the higher frequency wave of the A/D converterLON, wherein fLOFor local oscillator signal frequency, N ═ fRF/fADC_CLK，fRFIs the channel center frequency, fADC_CLKIs the operating frequency at which the digital demodulator performs optimally. The scheme of the invention enables the analog-digital converter and the digital demodulator to work at the optimal frequency according to the condition whether the channel is influenced by the higher harmonic wave of the working frequency of the analog-digital converter; or the working frequency is adjusted, so that the sensitivity attenuation of the channel is avoided.
Description
Technical Field
The invention relates to the technical field of radio frequency receivers, in particular to an adaptive sampling method of an analog-to-digital converter for improving the sensitivity attenuation of a radio frequency receiver, which relates to a System On Chip (SOC) for wireless communication.
Background
A communication protocol typically contains many channels. For example, the operating frequency range of the bluetooth communication protocol is 2402-2480 MHz, which comprises 79 signals in total, and each channel is separated by 1 MHz. The working frequency of the low-power-consumption Bluetooth communication protocol is 2402-2480 MHz, but the low-power-consumption Bluetooth communication protocol only comprises 40 channels, and each channel is spaced by 2 MHz. In actual work, two communication parties synchronously switch channels according to a protocol or a certain rule so as to avoid the defect that the communication parties are easily interfered by a high-power signal with a certain external fixed frequency when working in a fixed channel. Fig. 1 is a schematic diagram of 40 channels specified by the bluetooth low energy communication protocol.
Radio frequency receivers are an important component of wireless communication systems. In a wireless communication system, a radio frequency receiver receives a signal sent by a communication object, and extracts useful information for system analysis through a series of processing.
The sensitivity of a radio frequency receiver refers to the minimum signal level that the receiver can detect to meet performance requirements. The smaller the sensitivity of the receiver, the smaller the minimum signal that can be received and the longer the effective communication distance.
The receiver may have a different structure. According to the frequency of frequency conversion, the frequency conversion can be divided into primary frequency conversion and secondary frequency conversion. According to the intermediate frequency after frequency conversion, the frequency can be divided into zero intermediate frequency, low intermediate frequency, high intermediate frequency and the like.
Taking a single-conversion low-if rf receiver as an example (the structure is also the case for receivers with other structures), the structure generally includes modules such as an antenna, a low noise amplifier, a mixer, a local oscillator signal generator, a filter, an analog-to-digital converter, and a digital demodulator. The analog-to-digital converter samples at a certain working frequency, converts the intermediate-frequency analog signal into a digital signal, and sends the digital signal to the digital demodulator for processing to obtain useful information. The digital demodulator typically includes a digital frequency shifter, filter, etc., which also operates at a certain clock frequency. Typically the operating frequency of the digital demodulator is the same as the operating frequency of the analog-to-digital converter to facilitate the synchronous processing of the digital circuit. Meanwhile, the digital demodulator needs to set the optimal internal parameters according to the working frequency so as to achieve the optimal filtering and demodulating effects. Therefore, in general, in the design of the radio frequency receiver, the operating frequencies of the analog-to-digital converter and the digital demodulator are fixed and cannot be changed freely. If the operating frequencies of the analog-to-digital converter and the digital demodulator vary in different channels, different compensation measures are required in the different channels, otherwise the performance of the radio frequency receiver is affected.
In practical chip design, both the analog-to-digital converter and the digital demodulator operate at a certain clock frequency. In operation, this clock frequency inevitably generates a large number of higher harmonics. And these higher harmonics are most likely to fall within the operating frequency range of the communication protocol. For example, if the analog-to-digital converter and digital demodulator operate at 32MHz, then the 32MHz 76 th harmonic (2432MHz) and 77 th harmonic (2464MHz) will fall within the operating frequency range of the Bluetooth communication system.
These higher harmonics are transmitted back to the antenna or low noise amplifier through various physical or spatial couplings in the actual chip, and may be superimposed on the desired signal, resulting in degradation of the receiver sensitivity. For example, assuming the clocks of the analog-to-digital converter and the digital demodulator are 32MHz, their 76 th harmonic generates a harmonic component of-70 dBm at 2432MHz, and by reverse coupling, a harmonic of-100 dBm reaches the antenna and is superimposed on the wanted signal. At this time, if the receiver receives only-90 dBm of useful signal energy in the 2432MHz channel, the receiver may not be able to correctly receive the useful signal in the 2432MHz channel (the receiver sensitivity of bluetooth communication systems and bluetooth low energy communication systems is generally less than-90 dBm. the sensitivity of gps and other communication systems is even less than-150 dBm. the receiver receives the useful signal and demodulates it, and needs a certain signal-to-noise ratio, for example, 15 dB. in the foregoing example, the energy of the 76 th harmonic of the operating frequency of the analog-to-digital converter coupled to the antenna-100 dBm can be regarded as noise, and the energy of the useful signal is only-90 dBm, so the signal-to-noise ratio is only 10dB and cannot be correctly demodulated by the demodulator). This phenomenon is called receiver sensitivity fading.
In order to solve the problem of sense of the receiver in some channels caused by the higher harmonics of the analog-to-digital converter and the digital demodulator, the following methods are often adopted in practical design:
1. the power supply and the ground of circuits such as an analog-digital converter, a digital demodulator and the like which generate higher harmonics are physically separated from the radio frequency front end. And a large number of filter circuits are added. This requires an additional set of voltage modulators. Such as LDO, etc. The inserted large amount of filter circuits also consumes a certain chip area.
2. The radio frequency front end, the analog-to-digital converter, the digital demodulator and the like are separated by a certain distance in space. This inevitably results in a waste of chip area.
3. Working frequency f of analog-to-digital converterADC_CLK＝fLOThe technique of/N. Wherein f isLOIs the operating frequency of the local oscillator of the radio frequency receiver, N is oneA fixed integer. In addition to zero intermediate frequency radio frequency receivers, fLOWith the frequency f of the useful signalRFAll of which are different. With this technique, f can be adjustedADC_CLKHigher harmonics of (a) and (f)RFIs staggered so that fADC_CLKThe higher harmonics do not contribute to the sensitivity of the radio frequency receiver. However, in this way, the digital demodulators for most channels do not operate at the optimum operating frequency, and cannot achieve the optimum performance, and additional compensation is required. For example, in the case of a bluetooth communication system, it is assumed that the optimum operating frequency of the analog-to-digital converter and the digital demodulator is 32MHz, while f is assumedIF1MHz, the receiver is a single conversion structure, then fLO＝fRF-1 MHz. N is fixed at 76. At 2402MHz, f of channelADC_CLK2401/76 MHz, channel 2432MHz, fADC_CLK2431/76-31.986 MHz, at 2480MHz, fADC_CLK2479/76 MHz 32.618 MHz. The working frequency of the digital demodulator of all channels has a certain deviation relative to the optimal frequency of 32MHz, and the deviation range is approximately-1.3% -1.93%. To maintain optimal demodulation performance, special compensation is required, which results in a complicated design and wastes a certain chip area.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: in view of the problems, an adaptive sampling method for an analog-to-digital converter is provided, which improves the sensitivity attenuation of a radio frequency receiver.
The technical scheme adopted by the invention is as follows: an adaptive sampling method of an analog-to-digital converter for improving sensitivity attenuation of a radio frequency receiver comprises the following steps: setting the working frequency of the digital demodulator as the working frequency with optimal performance, wherein the sampling frequency of the analog-to-digital converter is equal to the frequency of the digital demodulator; in a channel which is not influenced by high-order frequency waves of the analog-to-digital converter, the sampling frequency of the analog-to-digital converter and the working frequency of the digital demodulator are fixed; switching the sampling frequency of the A/D converter and the working frequency of the digital demodulator to f in the channel affected by the higher frequency wave of the A/D converterLON, wherein fLOFor local oscillator signal frequency, N ═ fRF/fADC_CLK，fRFIs the channel center frequency, fADC_CLKIs the operating frequency at which the digital demodulator performs optimally.
Further, the channels not affected by the higher frequency wave of the analog-to-digital converter are: channels that are not integer multiples of the operating frequency for optimum digital demodulator performance.
Further, the channels affected by the higher frequency waves of the analog-to-digital converter are: is a channel of integral multiple of the operating frequency for optimum performance of the digital demodulator.
Furthermore, the radio frequency receiver is provided with a frequency divider and a multiplexer, the frequency divider divides the frequency of the LO in a channel of which the frequency is an integral multiple of the optimal working frequency of the digital demodulator, and the multiplexer is used for selecting the sampling frequency of the analog-to-digital converter of the corresponding channel and the working frequency of the digital demodulator.
Compared with the prior art, the beneficial effects of adopting the technical scheme are as follows: by adopting the technical scheme of the invention, the analog-digital converter and the digital demodulator work at the optimal frequency or the working frequency is adjusted according to the condition whether the channel is influenced by the higher harmonic wave of the working frequency of the analog-digital converter:
in a channel which is not affected by higher harmonics of the working frequency of the analog-to-digital converter, the analog-to-digital converter and the digital demodulator work at the optimal frequency, and the performance is excellent. In the channel affected by the higher harmonics of the analog-to-digital converter, the working frequency of the analog-to-digital converter is converted into LO/N (N can be changed along with the change of the channel) which is closest to the optimal working frequency, and the higher harmonics of the analog-to-digital converter are converted into zero intermediate frequency after being mixed, so that the useful signals cannot be affected. Sensitivity attenuation in this channel due to higher harmonics of the analog-to-digital converter and digital demodulator operating frequencies is thus avoided. And the working frequency of the analog-to-digital converter and the digital demodulator is very close to the optimal frequency, and the influence on the performance of the digital demodulator is weak.
Based on the adjusting method of the invention, only a frequency divider and a multiplexer with small area need to be added in the radio frequency receiver, and the sense of the receiver can be improved with simple structure and small cost.
Drawings
Fig. 1 is a schematic representation of the channels and operating frequency ranges of a prior art low power bluetooth communication protocol.
Fig. 2 is a schematic diagram of the adaptive sampling method of the analog-to-digital converter for improving the sensitivity attenuation of the radio frequency receiver according to the invention.
Fig. 3 is a schematic diagram of an adaptive sampling method of an analog-to-digital converter for improving the sensitivity attenuation of a radio frequency receiver in a bluetooth communication system.
Fig. 4 is a schematic structural diagram of a radio frequency receiver in an embodiment of the present invention; the spectrum diagram in the figure is as follows: after the invention is adopted in the channel affected by the sense phenomenon, the useful signal output by each module and the corresponding sampling frequency higher harmonic of the analog-to-digital converter.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Let f be the operating frequency at which the performance of the digital demodulator is optimal (i.e. the sampling frequency of the analog-to-digital converter)ADC_CLK. Digital demodulator at fADC_CLKOperating at this frequency, has the best demodulation capability. If the frequency is slightly deviated, the demodulation capability is degraded. In this example, take fADC_CLK＝32MHz。
At a value other than fADC_CLKInteger multiples of the channel, i.e. fRF！＝N*fADC_CLK. Wherein f isRFIs the channel center frequency, and N is an integer. The higher harmonics of the working frequency of the A/D converter will not follow fRFOverlapping does not affect the demodulation of the useful signal. The analog-to-digital converter and the digital demodulator still operate at the optimized optimum frequency, i.e. 32MHz in this embodiment. After passing through the multiplexer, not f, as shown in FIG. 2ADC_CLKThe sampling frequency of the analog-to-digital converter and the working frequency of the digital demodulator of the integral multiple of the channel are still fixed to the optimal working frequency.
At fADC_CLKInteger multiples of channels, i.e. fRF＝N*fADC_CLK. The higher harmonics of the adc and the digital demodulator cause a sensitivity drop (sense), which adjusts the operating frequency of the adc and the digital demodulator. The embodiment adopts the locality in the radio frequency receiverThe oscillator is divided by an integer N to implement the change of the operating frequency (sampling frequency) of the analog-to-digital converter, and the integer is adjusted according to the change of the channel.
The specific practice based on the integer is as follows:
calculating integral multiple relation between channel center frequency and analog-digital converter sampling frequency, N ═ fRF/fADC_CLKWherein f isRFIs the channel center frequency, fADC_CLKIt is the operating frequency at which the performance of the analog-to-digital converter and the digital demodulator is optimal.
In this channel, the sampling frequency (operating frequency) of an analog-to-digital converter (ADC) is switched to f by a multiplexerLON, wherein fLOIs the local oscillator signal frequency.
Take the Bluetooth communication system as an example, if fADC_CLKAt 32MHz, the higher harmonics of the ADC operating frequency may cause desense at both 2432MHz and 2464MHz channels. Among them, 2432MHz is 32MHz 76, and 2464MHz is 32MHz 77. Suppose that our chip design uses fIF1MHz, then at 2432MHz this channel, fLO2431MHz, a/d converter operating frequency fADC_CLK_24322431 MHz/76-31.98684 MHz (as in channel 2 of fig. 3); at 2464MHz, fLO2463MHz, analog-to-digital converter operating frequency fADC_CLK_24642463MHz/77 31.987MHz (as in channel 3 of fig. 3); other than 2432MHz and 2464MHzADC_CLKAn integer multiple of channels (e.g., channel 1 in fig. 3), still fixed at the optimum operating frequency of 32 MHz; thus, by changing the operating frequencies of the analog-to-digital converter and the digital demodulator, higher harmonic interference coupled to the RF front end during operation of the analog-to-digital converter and the digital demodulator is converted to a zero intermediate frequency (f)IF0) and the wanted signal is converted to a low intermediate frequency (f)IF1MHz), the interference generated by the sampling frequency of the analog-to-digital converter and the higher harmonics of the operating frequency of the digital demodulator can be effectively distinguished from the useful signal after passing through the filters in the subsequent digital demodulator. In the channel where the sense phenomenon originally occurs, the analog-to-digital conversionOperating frequency f of digital demodulatorADC_CLKAdjusted digital demodulator performance optimal working frequency f relative to other channelsADC_CLK(optimum performance value) there is only a little change (in the above example, 2432MHz, f for the channelADC_CLK_2432The variation is only 0.04% with respect to the optimum operating frequency, and 2464MHz, f for the channelADC_CLK_2464Relative to the optimum operating frequency, the variation is also only 0.04%), with negligible impact on digital demodulator performance.
Fig. 4 is a schematic diagram of a radio frequency receiver, in which an antenna, a low noise amplifier, a mixer, a filter, an analog-to-digital converter, and a digital demodulator are connected in sequence, the local oscillator is connected to the mixer, and an output of the local oscillator is also connected to a frequency divider, and an output of the frequency divider is connected to an input terminal of a multiplexer. In fig. 4, the outputs of the multiplexers are the sampling clock of the analog-to-digital converter and the operating clock of the digital demodulator, the local oscillator supplies both the local oscillator signal (LO) to the mixer and the LO to the frequency divider, which operates on the channels affected by the aforementioned sense phenomenon (e.g., signals 2432MHz and 2464MHz in the aforementioned example), and the multiplexer selects the output of the frequency divider to be supplied to the analog-to-digital converter and the digital demodulator according to the channel by dividing the LO by different integers. In channels that are not affected by the sense phenomenon, the multiplexer output is fixed to a clock signal that optimizes the performance of the digital demodulator. The spectrum diagram shown in fig. 4 is: after the invention is adopted in the channel affected by the sense phenomenon, the useful signal output by each module and the corresponding sampling frequency higher harmonic of the analog-to-digital converter are obtained.
The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed. Those skilled in the art to which the invention pertains will appreciate that insubstantial changes or modifications can be made without departing from the spirit of the invention as defined by the appended claims.
Claims (3)
1. An adaptive sampling method for an analog-to-digital converter for improving sensitivity attenuation of a radio frequency receiver is characterized by comprising the following steps: setting the working frequency of the digital demodulator as the working frequency with optimal performance, wherein the sampling frequency of the analog-to-digital converter is equal to the frequency of the digital demodulator; in a channel which is not influenced by high-order frequency waves of the analog-to-digital converter, the sampling frequency of the analog-to-digital converter and the working frequency of the digital demodulator are fixed; switching the sampling frequency of the A/D converter and the working frequency of the digital demodulator to f in the channel affected by the higher frequency wave of the A/D converterLON, wherein fLOFor local oscillator signal frequency, N ═ fRF/fADC_CLK，fRFIs the channel center frequency, fADC_CLKThe working frequency with optimal performance of the digital demodulator;
the radio frequency receiver is provided with a frequency divider and a multiplexer, the frequency divider divides the frequency of the local oscillation signal in a channel with the frequency being integral multiple of the optimal working frequency of the digital demodulator, and the multiplexer is used for selecting the sampling frequency of the analog-to-digital converter of the corresponding channel and the working frequency of the digital demodulator.
2. The adaptive sampling method for analog-to-digital converter with improved sensitivity attenuation of radio frequency receiver as claimed in claim 1, wherein said channels not affected by higher frequency waves of analog-to-digital converter are: channels that are not integer multiples of the operating frequency for optimum digital demodulator performance.
3. The adaptive sampling method for analog-to-digital converter with improved sensitivity attenuation of radio frequency receiver as claimed in claim 2, wherein said channels affected by higher frequency waves of analog-to-digital converter are: is a channel of integral multiple of the operating frequency for optimum performance of the digital demodulator.
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| JP2011188181A (en) * | 2010-03-08 | 2011-09-22 | Kenwood Corp | Receiver and receiving method |
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| JP2011188181A (en) * | 2010-03-08 | 2011-09-22 | Kenwood Corp | Receiver and receiving method |
| CN102096656A (en) * | 2010-11-19 | 2011-06-15 | 中国船舶重工集团公司第七○九研究所 | GHz level ADC (Analog to Digital Converter) interface IP core |
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