US20160294591A1

US20160294591A1 - Multichannel receiver

Info

Publication number: US20160294591A1
Application number: US14/675,100
Authority: US
Inventors: Boris A. Kurchuk; Walter Honcharenko
Original assignee: Alcatel Lucent USA Inc
Current assignee: Nokia of America Corp
Priority date: 2015-03-31
Filing date: 2015-03-31
Publication date: 2016-10-06
Also published as: US10218400B2; US20170149465A1

Abstract

An embodiment of the disclosed multichannel receiver may use a single master clock to generate (i) the sampling-clock signal that sets the sampling rate of the receiver's ADC and (ii) multiple electrical local-oscillator signals that are used in various channels of the receiver's analog down-converter to translate to intermediate frequency the RF signals received on the receiver's array of antennas. The multichannel receiver may employ a plurality of interconnected frequency dividers configured to variously divide the master-clock frequency to generate the sampling-clock signal and the multiple local-oscillator signals in a manner that causes these signals to have different respective frequencies.

Description

BACKGROUND

1. Field
The present disclosure relates to communication equipment and, more specifically but not exclusively, to radio-frequency (RF) receivers.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Recent development of very high-speed, high-resolution, and high-dynamic-range linear analog-to-digital converters (ADCs) enables implementation of certain RF-receiver functions using a digital signal processor (DSP) instead of the analog RF hardware conventionally used for these purposes in the previous generation of RF receivers. However, the use of wider bandwidths, multiple spectral bands, and/or spectrum sharing introduces new challenges to the receiver design.

SUMMARY OF SOME SPECIFIC EMBODIMENTS

Whereas multichannel-receiver architectures often need local oscillator (LO) signals in multiple spectral bands, a phase-lock loop (PLL) for providing a LO signal is a relatively complex circuit. Such a circuit can take up a relatively large chip area and/or consume considerable power. In addition, a PLL may result in an increased level of electromagnetic interference (EMI), ground bouncing, frequency pulling, and other deleterious effects that tend to degrade the overall receiver performance.
An embodiment of a disclosed multichannel receiver may use a single master clock to generate (i) the sampling-clock signal that sets the sampling rate of the receiver's ADC and (ii) multiple electrical local-oscillator signals that are used in various channels of the receiver's analog down-converter to translate to intermediate frequency the RF signals received on the receiver's array of antennas. The multichannel receiver may employ a plurality of interconnected frequency dividers configured to variously divide the master-clock frequency to generate the sampling-clock signal and the multiple local-oscillator signals in a manner that causes these signals to have different respective frequencies. The use of a single master clock may advantageously enable the multichannel receiver to have a smaller size, consume less power, and exhibit lower levels of phase noise and EMI than conventional receivers that rely on multiple PLLs to generate sampling-clock and local-oscillator signals.
According to one embodiment, a multichannel receiver comprises: a plurality of mixers, each one of the plurality of mixers being configured to mix a respective one of a plurality of electrical RF signals and a respective one of a plurality of electrical LO signals to generate a respective one of a plurality of electrical intermediate-frequency (IF) signals, each electrical LO signal of the plurality of LO signals having a different frequency; an ADC configured to convert the electrical IF signals into a corresponding digital IF signal carrying a sequence of discrete digital samples generated by the ADC at a sampling rate determined by a sampling-clock signal; and a plurality of frequency dividers configured to frequency divide a master-clock signal to generate the sampling-clock signal and the plurality of electrical LO signals of different frequencies.
According to another embodiment, a receiver comprises: a first mixer configured to mix a first electrical RF signal and a first electrical LO signal to generate a first electrical IF signal; an ADC configured to convert the first electrical IF signal into a corresponding digital IF signal carrying a sequence of discrete digital samples generated by the ADC at a sampling rate determined by a sampling-clock signal; a first clock generator configured to generate a master-clock signal; a first frequency divider configured to frequency divide the master-clock signal to generate the first electrical LO signal; and a second frequency divider configured to frequency divide the master-clock signal to generate the sampling-clock signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and benefits of various disclosed embodiments will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which:

FIG. 1 shows a block diagram of an RF receiver according to one embodiment;

FIG. 2 shows a block diagram of a DSP that can be used in an embodiment of the RF receiver shown in FIG. 1;

FIGS. 3A-3E graphically illustrate the operation of an example embodiment of the RF receiver shown in FIG. 1 employing the DSP shown in FIG. 2;

FIG. 4 shows a block diagram of a divider circuit that can be used in an alternative embodiment of the RF receiver shown in FIG. 1; and

FIG. 5 shows a block diagram of an RF receiver according to an alternative embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a radio-frequency (RF) receiver 100 according to one embodiment. Receiver 100 is illustratively shown in FIG. 1 as having n channels, where n is a positive integer greater than or equal to two. A person of ordinary skill in the art will understand that engineering constraints may impose an upper limit on the maximum number of channels that an embodiment of receiver 100 can have in practice. Various embodiments of receiver 100 may be used in cellular base stations and/or user equipment compatible with carrier-aggregation (CA) and multiple-input/multiple-output (MIMO) signal-transmission technologies.
Receiver 100 comprises an array of antennas 102 ₁-102 _n, each coupled to a respective one of RF front-end (FE) circuits 106 ₁-106 _n. In operation, each antenna 102 _iconverts a received electromagnetic wave into a corresponding electrical RF signal 104 _i, where i=1, 2, . . . , n. Each FE circuit 106 _ithen transforms electrical signal 104 _igenerated by antenna 102 _iinto a corresponding electrical RF signal 108 _imore suitable for down-conversion to intermediate frequency (IF) in a multichannel down-converter 110. In an example embodiment, the signal transformation performed in FE circuit 106 _imay include, but is not limited to (i) signal amplification to compensate for transmission losses and (ii) rejection of possible out-of-band noise and interference. These operations can be achieved, e.g., as known in the art, using one or more low-noise amplifiers (LNAs) and one or more filter stages, respectively (not explicitly shown in FIG. 1).
Multichannel down-converter 110 includes a plurality of mixers 112 ₁-112 _n, each configured to mix the corresponding one of electrical signals 108 ₁-108 _nwith a corresponding one of electrical local-oscillator (LO) signals 116 ₁-116 _n. Each of the resulting translated electrical signals 118 ₁-118 _nmay optionally be filtered in a respective band-pass filter (not explicitly shown in FIG. 1) and then combined, in a signal combiner 120, with the other translated electrical signals 118 to generate a combined electrical signal 124. An anti-aliasing filter 130 then passes through a useful portion of combined electrical signal 124 while rejecting the unwanted signal components. A resulting filtered electrical signal 132 generated by filter 130 is applied to an analog-to-digital converter (ADC) 140. The frequencies of LO signals 116 ₁-116 _nand the characteristics of anti-aliasing filter 140 are selected such that electrical signal 132 is an IF signal located within a designated IF band.
In an example embodiment, ADC 140 is an RF-sampling ADC (RF-ADC) that has a relatively high resolution and a relatively high dynamic range, and is capable of sampling IF signal 132 at a sampling rate that is higher, by at least a factor of two, than the bandwidth of this IF signal. RF-ADCs that can be used as ADC 140 are commercially available from several vendors. For example, Texas Instruments Inc. and Analog Devices Inc. offer for sale two families of direct RF-sampling ADCs under the product codes ADC32RFXX and AD96XX, respectively. A person of ordinary skill in the art will be able to select, from those two families, a suitable ADC for use in an embodiment of receiver 100.
A digital electrical signal 142 generated by ADC 140 is applied to a digital signal processor (DSP) 150 configured to recover the data encoded in the electromagnetic wave received by antennas 102 ₁-102 _n. The digital signal processing implemented in DSP 150 may include, but is not limited to (i) digital down-conversion from the designated IF band to baseband, (ii) digital filtering, and (iii) data decoding. The recovered data are directed to external circuits via an electrical output signal 152.
LO signals 116 ₁-116 _nand a sampling-clock signal 138 that clocks ADC 140 are generated using a master-clock generator 160. More specifically, master-clock generator 160 is configured to generate a master-clock signal 162 having a relatively high frequency (see example values given in the text below), sufficiently low jitter, and sufficiently fast slew rate. In an example embodiment, master-clock generator 160 may be implemented using a PLL. The output of the voltage-controlled oscillator (VCO) in the PLL may be buffered, e.g., as known in the art, to cause master-clock signal 162 to have the aforementioned desired characteristics.
A plurality of frequency dividers 170 ₀-170 _nare configured to variously divide the frequency of master-clock signal 162 to generate divided-frequency signals 172 ₀-172 _n, respectively. Each of divided-frequency signals 172 ₀-172 _ntypically has multiple frequency components that include a respective main divided frequency and also higher harmonics and/or sub-harmonics of the main divided frequency. The main divided frequency in a divided-frequency signal 172 _kgenerated by frequency divider 170 _kis lower than the frequency of master-clock signal 162 by a fixed division factor M_k(also see FIG. 1), where k=0, 1, 2, . . . , n. In various embodiments, the set of division factors M_kmay include integer values or mixed fractional values, or some combination of both.
In some embodiments, frequency dividers 170 ₀-170 _nmay benefit from or be implemented using circuits disclosed in the following publications: (i) Benzad Razavi, “RF Microelectronics,” Prentice Hall, 1998, pp. 290-297; (ii) Louis Fan Fei, “Frequency Divider Design Strategies,” Broadband Technology, March 2005; (iii) Mohit Arora, Clock Dividers Made Easy, SNUG Boston, 2002; and (iv) Myung-Woon Hwang, Jong-Tae Hwang, and Gyu-Hyeong Cho, “Design of high-speed CMOS prescaler,” IEEE APC on ASICs, 2000. These publications are incorporated herein by reference in their entirety.
A filter 174 _ilocated between frequency divider 170 and mixer 112 _iis configured to generate LO signal 116 _iby passing through the main divided frequency of signal 172 _i, while stopping, attenuating, and/or rejecting the higher-order harmonics and, in some embodiments, also the sub-harmonics thereof. In an example embodiment, filters 174 ₁-174 _ncan be implemented as low-pass filters. In an alternative embodiment, filters 174 ₁-174 _ncan be implemented as band-pass filters.
A filter 180 located between frequency divider 170 ₀and ADC 140 generates sampling-clock signal 138 by passing through the main divided frequency of signal 172 ₀and a predetermined number of the odd higher harmonics thereof, while stopping or rejecting the other harmonics and sub-harmonics of the main divided frequency, and possibly noise that may be coupled to the sampling-clock channel due to EMI, the presence of power-supply noise, and/or via any other coupling mechanism. A representative filter that can be used as filter 180, as well as representative benefits of its use in generating the sampling-clock signal of an ADC, such as ADC 140, are described in commonly owned U.S. Patent Application Publication No. 2014/0210536, which is incorporated herein by reference in its entirety.
An example embodiment of receiver 100 may be implemented as an RF integrated circuit (IC) or chipset. For example, in one embodiment, receiver 100 may be implemented using the following three ICs: (i) an RF-ADC IC, e.g., containing ADC 140; (ii) a multiband down-converter IC, e.g., containing down-converter 110 and, optionally, a circuit portion 190 indicated by the corresponding dashed rectangle in FIG. 1; and (iii) a DSP IC, e.g., containing DSP 150. Alternatively, receiver 100 may be implemented using the following two ICs: (i) an RF IC, e.g., containing ADC 140, down-converter 110, and circuit portion 190; and (ii) a DSP IC, e.g., containing DSP 150. Other alternative breakdowns of the receiver structure into discrete ICs are also possible. For example, certain parts of FE circuits 106 ₁-106 _n, such as a variable-gain amplifier (or variable attenuator), may be included into the IC containing down-converter 110 IC or into the RF IC containing ADC 140, down-converter 110, and circuit portion 190. In some embodiments, filters 174 ₁-174 _nand 130, and possibly the optional filters configured to filter translated electrical signals 118 ₁-118 _ncan be tunable, e.g., to increase flexibility of the IC usage and to accommodate different possible operating-frequency bands of the corresponding multiband receiver.
The architecture of receiver 100 may provide one or more of the following benefits.
An example embodiment of receiver 100 uses a single common PLL (e.g., located in 160, FIG. 1) to generate multiple LO signals (e.g., 116 ₁-116 _n, FIG. 1) and the sampling-clock signal (e.g., 138, FIG. 1) for the RF-ADC. As a result, receiver 100 may have a smaller size, lower cost, and/or lower power consumption than comparably performing conventional receivers employing multiple PLLs. In addition, phase coherence across the signal paths in receiver 100 may be improved due to the substantial elimination of a distributed, conventionally used PLL network. Furthermore, receiver 100 may exhibit a reduced level of phase noise and/or EMI due to the absence of inter-PLL crosstalk.
An example embodiment of receiver 100 may be used for applications where low cost and enhanced performance are simultaneously required.
The use of filter 180 positively contributes to the improved signal-to-noise ratio (SNR), sensitivity, and blocking exhibited by receiver 100.
The use of a chipset, e.g., as outlined above, in an embodiment of receiver 100 may result in further size and/or cost reduction. Reduced power consumption may also reduce the junction temperature of one or more of the ICs in the chipset, which may positively contribute to the overall reliability of the receiver and of the corresponding wireless communication system.
FIG. 2 shows a block diagram of a DSP 200 that can be used in an embodiment of DSP 150 (FIG. 1). For illustration purposes, DSP 200 is shown in FIG. 2 as being configured to receive digital electrical signal 142 and to generate electrical output signal 152. A person of ordinary skill in the art will understand that alternative configurations of DSP 200 are also possible.
DSP 200 comprises a digital down-converter 202 and a digital demodulator 204. Digital down-converter 202 is configured to translate digital signal 142 to one or more baseband channels for demodulation and decoding in digital demodulator 204. Frequency translation is achieved by digitally mixing, in digital mixers 220 ₁-220 _n, (i) a plurality of portions 212 ₁-212 _nof digital electrical signal 142 generated by a digital signal splitter 210 and (ii) a plurality of digital LO signals 216 ₁-216 _ngenerated by numerically controlled oscillators (NCOs) 214 ₁-214 _n, respectively, as indicated in FIG. 2. Each of the resulting mixed digital signals 222 ₁-222 _nis filtered in a respective one of digital filters 230 ₁-230 _nto generate a respective one of digital baseband signals 232 ₁-232 _n. Digital filters 230 ₁-230 _ntypically operate to provide decimation and baseband-channel selectivity. More specifically, the frequencies of digital LO signals 216 ₁-216 _nand the band-pass characteristics of digital filters 230 ₁-230 _nare selected, e.g., according to a predefined frequency plan. Digital demodulator 204 operates generate electrical output signal 152 by demodulating and decoding digital baseband signals 232 ₁-232 _n.
NCOs 214 ₁-214 _ngenerate digital LO signals 216 ₁-216 _nusing a common (single) digital-reference-clock signal 208 generated by a digital clock generator 206. In some embodiments, digital-reference-clock signal 208 may optionally be provided, as a reference input signal, to the PLL in master-clock generator 160 (see FIG. 1). In such embodiments, all of LO signals 116 ₁-116 _n, sampling-clock signal 138 (FIG. 1), and digital LO signals 216 ₁-216 _n(FIG. 2) are generated in reference to a single common clock signal, i.e., digital-reference-clock signal 208. This configuration may be beneficial, e.g., because it may improve synchronization between ADC 140, down-converter 110, and DSP 150, reduce clock noise, and improve the overall phase coherence across all carriers/signals processed in the DSP.
In some embodiments, digital clock generator 206 may generate digital-reference-clock signal 208 based on an external clock reference signal 205.
FIGS. 3A-3E graphically illustrate the operation of an example embodiment of receiver 100 (FIG. 1) employing DSP 200 (FIG. 2). More specifically, the graphs shown in FIGS. 3A-3E illustrate an embodiment of receiver 100 having four channels (i.e., n=4) corresponding to a 4-channel MIMO system. FIG. 3A graphically shows the spectra of electrical signals 108 ₁-108 ₄(FIG. 1). FIG. 3B graphically shows the spectra of LO signals 116 ₁-116 ₄(FIG. 1). FIG. 3C graphically shows the spectrum of combined electrical signal 124 (FIG. 1). FIG. 3D graphically shows the spectra of digital LO (DLO) signals 216 ₁-216 ₄(FIG. 2). FIG. 3E graphically shows the spectra of digital baseband signals 232 ₁-232 _n(FIG. 2). Also note that the abscissas in the graphs shown in FIGS. 3A-3E have different scales, and the graph origins are not necessarily located at the zero (dc) frequency.
Referring to FIG. 3A, the spectral bands representing electrical signals 108 ₁-108 ₄have different amplitudes but are all centered on the same carrier frequency RF₀.
Referring to FIG. 3B, LO signals 116 ₁-116 ₄have frequencies LO1-LO4, respectively. Each of frequencies LO1-LO4 is generated by dividing the output frequency of the VCO (F_VCO) located in the PLL of master-clock generator 160 by a respective one of division factors M₁-M₄.
Referring to FIG. 3C, combined electrical signal 124 has four IF bands centered on frequencies IF1-IF4, respectively. The relationship between IF1-IF4 and LO1-LO4 is indicated in FIG. 3C.
Referring to FIG. 3D, DLO signals 216 ₁-216 ₄have frequencies DLO1-DLO4, respectively.
Referring to FIG. 3E, digital baseband signals 232 ₁-232 _nrepresent baseband channels BB1-BB4, respectively. These baseband signals can be generated, e.g., as indicated above in the description of digital down-converter 202 (FIG. 2), by translation to the baseband of the four IF bands shown in FIG. 3C.
In one embodiment, receiver 100 may be designed using the following frequency plan:

- F_VCO=2457.6 MHz;
- M₀=2, for the ADC sampling rate of 1228.8 MHz;
- M₁=8, for LO1=307.2 MHz;
- M₂=9, for LO2=273.07 MHz;
- M₃=10, for LO3=245.76 MHz; and
- M₄=11, for LO4=223.42 MHz.

In an alternative embodiment, receiver 100 may be designed using the following frequency plan:

- F_VCO=3072 MHz;
- M₀=2, for the ADC sampling rate of 1536 MHz;
- M₁=7, for LO1=438.85 MHz;
- M₂=8, for LO2=384 MHz;
- M₃=9, for LO3=341.33 MHz; and
- M₄=10, for LO4=307.2 MHz.

In yet another alternative embodiment, receiver 100 may be designed using the following frequency plan:

- F_VCO=3072 MHz;
- M₀=2, for the ADC sampling rate of 1536 MHz;
- M₁=7, for LO1=279.27 MHz;
- M₂=8, for LO2=256 MHz;
- M₃=9, for LO3=236.31 MHz; and
- M₄=10, for LO4=219.43 MHz.

Based on the above examples, a person of ordinary skill in the art will understand how to make additional alternative frequency plans for use in the corresponding alternative embodiments of receiver 100.
FIG. 4 shows a block diagram of a divider circuit 400 that can be used in an alternative embodiment of receiver 100 (FIG. 1). More specifically, divider circuit 400 may be used to replace the plurality of frequency dividers 170 ₀-170 _nin receiver 100. The electrical connections of divider circuit 400 to the rest of receiver 100 are indicated in FIG. 4 by signals 162 and 172 ₀-172 _n, which are also shown in FIG. 1.
Circuit 400 comprises a plurality of frequency dividers 470 ₀-470 _nthat are generally analogous to frequency dividers 170 ₀-170 _n. However, unlike frequency dividers 170 ₀-170 _nin receiver 100, which are connected in parallel to one another, frequency dividers 470 ₀-470 _nin circuit 400 are serially connected to one another. As a result, the main divided frequency of signal 172 _kin circuit 400 depends on the division factors M₀-M_kof all preceding frequency dividers 470 and can be expressed as F_VCO/(M₀×M₁× . . . ×M_k). In contrast, the main divided frequency of signal 172 _kin the embodiment of receiver 100 shown in FIG. 1 does not depend on division factors M₀-M_k-1and can be expressed as F_VCO/M_k.
A person of ordinary skill in the art will understand that various alternative connections of frequency dividers are also possible in a divider circuit configured to generate signals 172 ₀-172 _n. For example, in an alternative embodiment of the divider circuit, some frequency dividers may be connected serially with one another, while some other frequency dividers may be connected in parallel to one another.
FIG. 5 shows a block diagram of an RF receiver 500 according to an alternative embodiment. Receiver 500 can be built using some of the same functional blocks as those used in receiver 100 (FIG. 1). These functional blocks are labeled in FIG. 5 using the same numerals as in FIG. 1. The description of the reused functional blocks is not repeated here. Instead, the description of receiver 500 that is given below focuses primarily on the differences between receivers 100 and 500.
One difference between receivers 100 and 500 is that the latter receiver has a “complex” IF-signal-processing chain, as opposed to the “real” IF-signal-processing chain used in the former receiver. Receiver 500 implements the complex IF-signal processing using two parallel circuit planes, the elements of which are labeled using subscripts I and Q, respectively, where the “I” stands for “in-phase,” and the “Q” stands for “quadrature.” Receiver 500 employs a plurality of complex mixers 512 ₁-512 _nto generate appropriate input signals for the I and Q circuit planes. More specifically, a complex mixer 512 _igenerates a respective input signal for the I circuit plane by mixing, in its first mixer, a first copy of signal 108 _iand a first copy of LO signal 116 _i. Complex mixer 512 _ialso generates a respective input signal for the Q circuit plane by mixing, in its second mixer, a second copy of signal 108 _iand a relatively phase-shifted copy of the same LO signal 116 _ithat is generated in the complex mixer by applying a relative phase shift of approximately 90 degrees to a second copy of LO signal 116 _i.
A digital output signal 542 _Iof the I circuit plane is generated by ADC 140 _I. A digital output signal 542 _Qof the Q circuit plane is similarly generated by ADC 140 _Q. Both ADCs are clocked using sampling-clock signal 138. Digital signals 542 _Iand 542 _Qare applied to a DSP 550 for appropriate processing therein to recover the data encoded in the electromagnetic wave received by antennas 102 ₁-102 _n.
According to an example embodiment disclosed above in reference to FIGS. 1-5, provided is an apparatus (e.g., 100, FIG. 1; 500, FIG. 5) comprising: a multichannel down-converter (e.g., 110, FIG. 1) having a plurality of mixers (e.g., 112 ₁-112 _n, FIG. 1; 512 ₁-512 _n, FIG. 5), each configured to mix a respective one of a plurality of electrical RF signals (e.g., 108 ₁-108 _n, FIGS. 1, 5) and a respective one of a plurality of electrical LO signals (e.g., 116 ₁-116 _n, FIG. 1) to generate a respective one of a plurality of electrical IF signals (e.g., 118 ₁-118 _n, FIG. 1), wherein the multichannel down-converter is configured to combine said plurality of electrical IF signals to generate a combined electrical IF signal (e.g., 132, FIG. 1); an ADC (e.g., 140, FIG. 1) configured to sample the combined electrical IF signal at a sampling rate determined by a sampling-clock signal (e.g., 138, FIG. 1) to convert the combined electrical IF signal into a corresponding digital IF signal (e.g., 142, FIG. 1) carrying a sequence of discrete digital samples generated by the ADC at the sampling rate; and a plurality of interconnected frequency dividers (e.g., 170 ₀-170 _n, FIG. 1; 470 ₀-470 _n, FIG. 4) configured to divide a frequency of a master-clock signal (e.g., 162, FIG. 1) to generate the sampling-clock signal and the plurality of electrical LO signals.
In some embodiments of the above apparatus, the apparatus further comprises a first clock generator (e.g., 160, FIG. 1) configured to generate the master-clock signal.
In some embodiments of any of the above apparatus, the apparatus further comprises: a second clock generator (e.g., 206, FIG. 2) configured to generate a digital reference-clock signal (e.g., 208, FIG. 2); and a digital down-converter (e.g., 202, FIG. 2) configured to digitally translate the digital IF signal to baseband (e.g., as indicated in FIGS. 3C-3E) using the digital reference-clock signal. The first clock generator is configured to generate the master-clock signal using the digital reference-clock signal.
In some embodiments of any of the above apparatus, the digital down-converter is a part of a digital signal processor (e.g., 150, FIG. 1) configured to process the digital IF signal to recover data encoded in the plurality of electrical RF signals.
In some embodiments of any of the above apparatus, the digital down-converter comprises: a digital signal splitter (e.g., 210, FIG. 2) configured to split the digital IF signal into a plurality of digital portions (e.g., 212 ₁-212 _n, FIG. 2); a plurality of numerically controlled oscillators (e.g., 214 ₁-214 _n, FIG. 2) configured to generate a plurality of digital LO signals (e.g., 216 ₁-216 _n, FIG. 2) using the digital reference-clock signal; and a plurality of digital mixers (e.g., 220 ₁-220 _n, FIG. 2), each configured to mix a respective one of the plurality of digital portions and a respective one of the plurality of digital LO signals to generate a respective one of a plurality of digital baseband signals (e.g., 232 ₁-232 _n, FIG. 2), wherein the digital down-converter is configured to combine said plurality of digital baseband signals to generate a combined digital baseband signal (e.g., 242, FIG. 2) representing the digital IF signal.
In some embodiments of any of the above apparatus, the plurality of interconnected frequency dividers comprises two or more frequency dividers (e.g., 170 ₀-170 _n, FIG. 1), with each of said two or more frequency dividers being configured to receive a respective copy of the master-clock signal and further configured to divide the frequency of the master-clock signal by a respective division factor.
In some embodiments of any of the above apparatus, the plurality of interconnected frequency dividers comprises two or more frequency dividers (e.g., 470 ₀-470 _n, FIG. 4) that are serially connected to one another in a manner that causes a following one of the two or more frequency dividers to divide a frequency generated by a preceding one of the two or more frequency dividers.
In some embodiments of any of the above apparatus, one or more of the plurality of interconnected frequency dividers are configured to divide the frequency of the master-clock signal in a manner that causes different electrical LO signals of the plurality of electrical LO signals to have different respective frequencies.
In some embodiments of any of the above apparatus, some of the plurality of interconnected frequency dividers are further configured to divide the frequency of the master-clock signal in a manner that causes the sampling-clock signal to have a frequency that is different from any of the respective frequencies.
In some embodiments of any of the above apparatus, some of the plurality of interconnected frequency dividers are configured to divide the frequency of the master-clock signal in a manner that causes the sampling-clock signal to have a frequency that is different from a frequency of any other of the plurality of electrical LO signals.
In some embodiments of any of the above apparatus, the plurality of interconnected frequency dividers includes a set of frequency dividers, with each frequency divider in said set being configured to apply a respective integer frequency-division factor.
In some embodiments of any of the above apparatus, the set of frequency dividers is configured such that a set of integer values that consists of the respective integer frequency-division factors includes two or more consecutive integers (e.g., M₁=8, M₂=9, M₃=10, M₄=11).
In some embodiments of any of the above apparatus, the plurality of interconnected frequency dividers includes a set of frequency dividers, with each frequency divider in said set being configured to apply a respective fractional frequency-division factor.
In some embodiments of any of the above apparatus, the apparatus further comprises an array of antennas (e.g., 102 ₁-102 _n, FIG. 1). Each of the antennas is coupled to a respective one of RF front-end circuits (e.g., 106 ₁-106 _n, FIG. 1) configured to generate the respective one of the plurality of electrical RF signals based on an electrical input provided by a corresponding antenna.
In some embodiments of any of the above apparatus, the ADC (e.g., 140, FIG. 1; 140 ₁, 140 _Q, FIG. 5) is configured to operate in a single selected Nyquist zone (e.g., in the first or second Nyquist zone) or in more than one Nyquist zone (e.g., both in the first Nyquist zone and in the second Nyquist zone).
In some embodiments of any of the above apparatus, the multichannel down-converter is an analog electrical circuit.
In some embodiments of any of the above apparatus, the multichannel down-converter is a mixed-signal electrical circuit that includes an analog circuit portion and a digital circuit portion.
According to another example embodiment disclosed above in reference to FIGS. 1-5, provided is an apparatus comprising: an electrical analog down-converter (e.g., 110, FIG. 1) having a first mixer (e.g., 112 _i, FIG. 1) configured to mix a first electrical radio-frequency (RF) signal (e.g., 108 _i, FIG. 1) and a first electrical local-oscillator (LO) signal (e.g., 116 _i, FIG. 1) to generate a first electrical intermediate-frequency (IF) signal (e.g., 118 _i, FIG. 1), wherein the electrical analog down-converter is configured to convert the first electrical IF signal into a second electrical IF signal (e.g., 124 or filtered 118 _i, FIG. 1); an ADC (e.g., 140, FIG. 1) configured to sample the second electrical IF signal at a sampling rate determined by a sampling-clock signal (e.g., 138, FIG. 1) to convert the second electrical IF signal into a corresponding digital IF signal (e.g., 142, FIG. 1) carrying a sequence of discrete digital samples generated by the ADC at the sampling rate; a first clock generator (e.g., 160, FIG. 1) configured to generate a master-clock signal (e.g., 162, FIG. 1); a first frequency divider (e.g., 170 _i, FIG. 1) configured to divide a frequency of the master-clock signal to generate the first electrical LO signal; and a second frequency divider (e.g., 170 ₀, FIG. 1) configured to divide the frequency of the master-clock signal to generate the sampling-clock signal.
In some embodiments of the above apparatus, the first electrical LO signal and the sampling-clock signal have different respective frequencies.
In some embodiments of any of the above apparatus, the electrical analog down-converter includes a second mixer (e.g., 112 _j, i≠j, FIG. 1) configured to mix a second electrical RF signal (e.g., 108 _j, FIG. 1) and a second electrical LO signal (e.g., 116 _j, FIG. 1) to generate a third electrical IF signal (e.g., 118 _j, FIG. 1), wherein the electrical analog down-converter is configured to combine the first electrical IF signal and the third electrical IF signal to generate the second electrical IF signal. The apparatus further comprises a third frequency divider (e.g., 170 _j, FIG. 1) configured to divide the frequency of the master-clock signal to generate the second electrical LO signal.
In some embodiments of any of the above apparatus, the first electrical LO signal and the second electrical LO signal have different respective frequencies.
In some embodiments of any of the above apparatus, the apparatus further comprises a second clock generator (e.g., 206, FIG. 2) configured to generate a digital reference-clock signal (e.g., 208, FIG. 2); and a digital down-converter (e.g., 202, FIG. 2) configured to digitally translate the digital IF signal to baseband (e.g., as indicated in FIGS. 3C-3E) using the digital reference-clock signal. The first clock generator is configured to generate the master-clock signal using the digital reference-clock signal.
In some embodiments of any of the above apparatus, the apparatus further comprises a filter (e.g., an optional filter configured to filter 118 _i, not explicitly shown in FIG. 1) configured to generate the second electrical IF signal by filtering the first electrical IF signal.
While this disclosure includes references to illustrative embodiments, this specification is not intended to be construed in a limiting sense.
For example, in some embodiments, receiver 100 may be modified to be a single-channel receiver. The corresponding modification of receiver 100 may include removing or disabling all but one channel of down-converter 110, thereby transforming that down-converter into a single-channel down-converter.
Various modifications of the described embodiments, as well as other embodiments within the scope of the disclosure, which are apparent to persons skilled in the art to which the disclosure pertains are deemed to lie within the principle and scope of the disclosure, e.g., as expressed in the following claims.
Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value or range.
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this disclosure may be made by those skilled in the art without departing from the scope of the disclosure, e.g., as expressed in the following claims.
Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements.
The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the disclosure is indicated by the appended claims rather than by the description and figures herein. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
The description and drawings merely illustrate the principles of the disclosure. It will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.
The functions of the various elements shown in the figures, including any functional blocks labeled as “processors,” may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage. Other hardware, conventional and/or custom, may also be included.
It should be appreciated by those of ordinary skill in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the disclosure.

Claims

What is claimed is:

1. An apparatus comprising:

a plurality of mixers, each one of the plurality of mixers being configured to mix a respective one of a plurality of electrical radio-frequency (RF) signals and a respective one of a plurality of electrical local-oscillator (LO) signals to generate a respective one of a plurality of electrical intermediate-frequency (IF) signals, each electrical LO signal of the plurality of LO signals having a different frequency;

an analog-to-digital converter (ADC) configured to convert the electrical IF signals into a corresponding digital IF signal carrying a sequence of discrete digital samples generated by the ADC at a sampling rate determined by a sampling-clock signal; and

a plurality of frequency dividers configured to frequency divide a master-clock signal to generate the sampling-clock signal and the plurality of electrical LO signals of different frequencies.

2. The apparatus of claim 1, further comprising a first clock generator configured to generate the master-clock signal.

3. The apparatus of claim 2, further comprising:

a second clock generator configured to generate a digital reference-clock signal; and

a digital down-converter configured to digitally translate the digital IF signal to baseband using the digital reference-clock signal; and

wherein the first clock generator is configured to generate the master-clock signal in response to receiving the digital reference-clock signal.

4. The apparatus of claim 3, wherein the digital down-converter is a part of a digital signal processor configured to process the digital IF signal to recover data encoded in the plurality of electrical RF signals.

5. The apparatus of claim 3, wherein the digital down-converter comprises:

a plurality of numerically controlled oscillators configured to generate a plurality of digital LO signals in response to receiving the digital reference-clock signal; and

a plurality of digital mixers, each configured to mix a respective portion of the digital IF signal and a respective one of the plurality of digital LO signals to generate a respective one of a plurality of digital baseband signals.

6. The apparatus of claim 1, wherein the plurality of frequency dividers comprises two or more frequency dividers, with each of said two or more frequency dividers being configured to receive a respective copy of the master-clock signal and further configured to frequency divide the master-clock signal using a respective division factor.

7. The apparatus of claim 1, wherein the plurality of frequency dividers comprises two or more frequency dividers that are serially connected to one another in a manner that causes a following one of the two or more frequency dividers to divide a frequency generated by a preceding one of the two or more frequency dividers.

8. The apparatus of claim 1,

wherein the apparatus is configured to combine said plurality of electrical IF signals to generate a combined electrical IF signal; and

wherein the ADC is configured to convert the combined electrical IF signal into said corresponding digital IF signal carrying said sequence of discrete digital samples generated by the ADC at the sampling rate determined by the sampling-clock signal.

9. The apparatus of claim 8, wherein the plurality of frequency dividers are further configured to divide the frequency of the master-clock signal in a manner that causes the sampling-clock signal to have a frequency that is different from any LO frequency in the plurality of electrical LO signals.

10. The apparatus of claim 1, wherein the plurality of frequency dividers are configured to frequency divide the master-clock signal in a manner that causes the sampling-clock signal to have a frequency that is different from any LO frequency in the plurality of electrical LO signals.

11. The apparatus of claim 1, wherein each frequency divider of the plurality of frequency dividers is configured to produce a respective one of the electrical LO signals with a respective LO frequency such that a frequency of the master-clock signal is an integer multiple of the respective LO frequency.

12. The apparatus of claim 11, wherein the frequency dividers are configured to use integer frequency-division factors to frequency divide the master-clock signal, wherein a set of the integer frequency-division factors includes two or more consecutive integers.

13. The apparatus of claim 1, wherein each frequency divider of the plurality of frequency dividers is configured to produce a respective one of the electrical LO signals with a respective LO frequency such that a frequency of the master-clock signal is equal to the respective LO frequency multiplied by a mixed fractional value.

14. The apparatus of claim 1,

further comprising a receiver having an array of antennas; and

wherein each of the antennas is configured to generate the respective one of the plurality of electrical RF signals based on an electrical input provided by a corresponding antenna.

15. The apparatus of claim 1, wherein the multichannel down-converter is an analog electrical circuit.

16. An apparatus comprising:

a first mixer configured to mix a first electrical radio-frequency (RF) signal and a first electrical local-oscillator (LO) signal to generate a first electrical intermediate-frequency (IF) signal;

an analog-to-digital converter (ADC) configured to convert the first electrical IF signal into a corresponding digital IF signal carrying a sequence of discrete digital samples generated by the ADC at a sampling rate determined by a sampling-clock signal;

a first clock generator configured to generate a master-clock signal;

a first frequency divider configured to frequency divide the master-clock signal to generate the first electrical LO signal; and

a second frequency divider configured to frequency divide the master-clock signal to generate the sampling-clock signal.

17. The apparatus of claim 16, wherein the first electrical LO signal and the sampling-clock signal have different respective frequencies.

18. The apparatus of claim 16, further comprising:

a second mixer configured to mix a second electrical RF signal and a second electrical LO signal to generate a second electrical IF signal, wherein the ADC is further configured to convert the second electrical IF signal into a corresponding portion of the digital IF signal; and

the apparatus further comprises a third frequency divider configured to frequency divide the master-clock signal to generate the second electrical LO signal.

19. The apparatus of claim 18, wherein the first electrical LO signal and the second electrical LO signal have different respective frequencies.

20. The apparatus of claim 16, further comprising: