Automatic Image Rejection Calibration for Radar Systems Using Quadrature Transmitters and Receivers

Abstract

A method for automatic image rejection and monitoring of a frequency modulated continuous wave (FMCW) radar system includes generating a quadrature FMCW signal including an in-phase signal and a quadrature signal by a dual output FMCW signal generator. The in-phase signal and the quadrature signal are transmitted. A radar signal including a response in-phase signal and a quadrature signal is received in response to the transmitted in-phase signal and the quadrature signal. The response in-phase signal and the quadrature signal are provided to an analog-to-digital converter (ADC). An in-phase beat signal (Beat-I) and a quadrature beat signal (Beat-Q) are extracted from the ADC based on the received window signal. A phase calibration variable (θ t ) or the amplitude calibration variable (A t ) or both as inputs to a dual output FMCW signal generator to generate relative phase and / or amplitude adjustments.

Description

[Technical Field]

[0001] The present disclosure relates generally to radar systems, and more particularly to a system and method for calibrating quadrature imbalance in frequency modulated continuous wave radar systems. [Background technology]

[0002] Frequency-Modulated Continuous Wave (FMCW) radar refers to radar systems that emit continuous transmit power and can change their operating frequency during measurement by modulating the frequency and / or phase of the transmit signal. Typical FMCW radar systems are not used for wireless communications. In contrast, FMCW radar systems using quadrature transmitters (TX) and / or transceivers (TRX) can be configured for wireless communications. Such systems often transmit data using a baseband interface with two ports, in-phase (I) and quadrature (Q). To convert the base-frequency signal to a much higher frequency, these two signals are mixed using an upconversion mixer with a high-frequency signal and its quadrature signal. This combined output is then transmitted by an antenna. On the receiving side, the reverse process occurs, with a downconversion mixer generating and providing I and Q outputs. An IQ quadrature transceiver includes separate paths for the I and Q channels for the transmitter (TX) and receiver (RX), respectively.

[0003] To use an IQ transceiver for FMCW radar, the baseband IQ signals are phase shifted by 90 degrees relative to each other, sometimes called orthogonal. This has two main advantages: (i) it cuts the required bandwidth in half, and (ii) it avoids signal modulation due to IQ rotation at the receiver. Summary of the Invention

[0004] According to one embodiment, a frequency modulated continuous wave (FMCW) radar system includes a quadrature transceiver including a transmitter having an in-phase input and a quadrature input and a receiver having an in-phase output and a quadrature output. A dual-channel FMCW signal generator includes a first output coupled to the in-phase input of the transmitter and a second output coupled to the quadrature input of the transmitter. A first splitter is coupled between the first output of the dual-channel FMCW signal generator and the in-phase input of the transmitter. A second splitter is coupled between the second output of the dual-channel FMCW signal generator and the quadrature input of the transmitter. A first mixer includes a first input coupled to the second output of the first splitter, a second input coupled to the in-phase output of the receiver, and an output. A second mixer includes a first input coupled to the second output of the second splitter, a second input coupled to the quadrature output of the receiver, and an output. A dual-channel analog-to-digital converter (ADC) includes a first input coupled to the output of the first mixer and a second input coupled to the output of the second mixer. A controller is coupled between the programmable dual-channel FMCW signal generator and the dual-channel ADC.

[0005] In one embodiment, the dual channel FMCW signal generator is programmable.

[0006] In one embodiment, a dual channel FMCW signal generator is configured to provide a window signal that indicates the beginning and end of each frequency ramp cycle.

[0007] In one embodiment, the first power splitter and the second power splitter are two-way power splitters.

[0008] In one embodiment, the controller includes a quadrature calibration block configured to receive an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC.

[0009] In one embodiment, there is a low-pass filter on each input channel of the dual-channel ADC.

[0010] In one embodiment, the controller further includes a fast Fourier transform (FFT) block configured to receive the in-phase beat signal and the quadrature beat signal from the second output of the dual-channel ADC and provide a radar output. In one embodiment, pre-FFT or post-FFT averaging of the Beat-I signal and the Beat-Q signal can be used to improve the signal-to-noise ratio (SNR). In this way, the signal-to-noise ratio of the radar output is improved.

[0011] In one embodiment, the quadrature calibration block calculates the phase calibration variables (θ t ) or amplitude calibration variable (A t ) as an input to a dual-output FMCW signal generator.

[0012] In one embodiment, the dual channel FMCW signal generator is a digital circuit block.

[0013] In one embodiment, the controller calculates the initial quadrature calibration variables (θ t ,A t ) is configured to select the initial orthogonal calibration variables (θ t ,A t ) is applied as an input to a dual-output FMCW signal generator. The applied initial quadrature calibration variables (θ t ,A t ), an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC are received. The in-phase beat signal is correlated with the quadrature beat signal. If the correlation is determined to be below a predetermined threshold, a new quadrature calibration variable (θ t ,A t ) is selected.

[0014] According to one embodiment, a method for automatic image rejection in a frequency modulated continuous wave (FMCW) radar system includes generating a quadrature FMCW signal including an in-phase signal and a quadrature signal by a dual-output FMCW signal generator. The in-phase signal and the quadrature signal are transmitted via a transmitter of a transceiver. A radar signal including a response in-phase signal and a response quadrature signal is received in response to the transmitted in-phase signal and quadrature signal from the transceiver. The response in-phase signal and the response quadrature signal are provided to a dual-channel analog-to-digital converter (ADC). A controller receives a window signal indicating the start and end of a frequency ramp cycle of the generated quadrature FMCW signal. The controller extracts an in-phase beat signal (Beat-I) and a quadrature beat signal (Beat-Q) from the dual-channel ADC based on the received window signal. The controller correlates Beat-I with Beat-Q. The controller calculates a phase calibration variable (θ) based on the correlation. t ) or amplitude calibration variable (A t ) or both as inputs to a dual output FMCW signal generator to generate relative phase and / or amplitude adjustments.

[0015] In one embodiment, if it is determined that the threshold correlation has not been reached, the phase calibration variable (θ t ) or amplitude calibration value (A t ) or both are iteratively adjusted and fed as inputs to a dual-output FMCW signal generator.

[0016] In one embodiment, low-pass filtering is performed on each input channel of a dual-channel ADC.

[0017] In one embodiment, a first power splitter splits the in-phase signal of the FMCW signal into a first in-phase signal of the FMCW signal that is provided to the transmitter and a second in-phase signal of the FMCW signal that is provided as a first in-phase input to the first mixer, and a second power splitter splits the quadrature signal of the FMCW signal into a first quadrature signal of the FMCW signal that is provided to the transmitter and a second quadrature signal of the FMCW signal that is provided as a first quadrature input to the second mixer.

[0018] In one embodiment, a first mixer mixes a first in-phase input with an in-phase radar signal received by the receiver and provides the result as a first input to a dual-channel analog-to-digital converter (ADC), and a second mixer mixes a first quadrature input with a quadrature radar signal received by the receiver and provides the result as a second input to the dual-channel ADC.

[0019] In one embodiment, to enhance the calibration capabilities of an FMCW radar system, at least one of the transmitter orientation or the receiver orientation is adjusted to increase leakage current or signal reflections.

[0020] According to one embodiment, a method for calibrating a frequency modulated continuous wave (FMCW) radar system includes providing a quadrature transceiver including a transmitter having an in-phase input and a quadrature input and a receiver having an in-phase output and a quadrature output. A dual-channel FMCW signal generator is provided, including a first output coupled to the in-phase input of the transmitter and a second output coupled to the quadrature input of the transmitter. A first splitter is coupled between the first output of the dual-channel FMCW signal generator and the in-phase input of the transmitter. A second splitter is coupled between the second output of the dual-channel FMCW signal generator and the quadrature input of the transmitter. A first mixer is provided, including a first input coupled to the second output of the first splitter, a second input coupled to the in-phase output of the receiver, and an output. A second mixer is provided, including a first input coupled to the second output of the second splitter, a second input coupled to the quadrature output of the receiver, and an output. A dual-channel analog-to-digital converter (ADC) is provided, the dual-channel analog-to-digital converter (ADC) having a first input coupled to the output of the first mixer and a second input coupled to the output of the second mixer, and a controller is coupled between the dual-channel FMCW signal generator and the dual-channel ADC.

[0021] In one embodiment, a dual channel FMCW signal generator is configured to calculate a phase calibration variable (θ t ) or amplitude calibration variable (A t ) or both. The dual-channel FMCW signal generator receives the received phase calibration variable (θ t ) or amplitude calibration variable (A t ) or both.

[0022] In one embodiment, a window signal is provided by the dual channel FMCW signal generator to indicate the beginning and end of each frequency ramp cycle of the dual channel FMCW signal generator.

[0023] In one embodiment, a quadrature calibration block of the controller receives an in-phase beat signal from a first output of a dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC.

[0024] In one embodiment, each input channel of a dual-channel ADC is low-pass filtered.

[0025] In one embodiment, a fast Fourier transform (FFT) block of the controller receives a quadrature beat signal from a second output of the dual-channel ADC and provides a radar output based on the quadrature beat signal.

[0026] In one embodiment, the phase calibration variable (θ t ) or amplitude calibration variable (A t ) is provided as an input to a dual-output FMCW signal generator by the controller's quadrature calibration block.

[0027] In one embodiment, the FMCW signal generator is operated in the digital domain.

[0028] In one embodiment, the controller calculates the initial quadrature calibration variables (θ t ,A t ) The controller selects the initial quadrature calibration variables (θ t ,A t ) as input to the dual-output FMCW signal generator. The controller calculates the applied initial quadrature calibration variables (θ t ,A t ) from a first output of the dual-channel ADC and a quadrature beat signal from a second output of the dual-channel ADC. The controller correlates the in-phase beat signal with the quadrature beat signal. Upon determining that the correlation is below a predetermined threshold, the controller selects new quadrature calibration variables (θ t ,A t ).

[0029] The techniques described herein can be implemented in a number of ways, example implementations of which are described below with reference to the following drawings:

[0030] The drawings are of exemplary embodiments. The drawings do not depict all embodiments. Other embodiments may be used in addition to or instead of these. Details deemed obvious or unnecessary may be omitted to save space or for a more effective illustration. Some embodiments may use additional components or steps, or may be practiced without all of the components or steps shown, or both. The same numbers in different drawings refer to the same or similar components or steps. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a block diagram illustrating an architecture for calibrating in-phase and quadrature path imbalances in a frequency modulated continuous wave radar system using quadrature transmitters and receivers, according to an example embodiment. [Figure 2] FIG. 1 is a conceptual block diagram illustrating calibration of in-phase and quadrature imbalance in an FMCW radar system, according to an example embodiment. [Figure 3] FIG. 10 illustrates an example table of paths used for phase and amplitude calibration variables θt and At patterns, according to an example embodiment. [Figure 4] FIG. 10 is a more detailed block diagram illustrating an architecture for calibrating in-phase and quadrature path imbalances in a frequency modulated continuous wave radar system using quadrature transmitters and receivers, according to an example embodiment. [Figure 5A] FIG. 10 shows an example of the spectral response of the output of a quadrature transmitter TX before calibration. [Figure 5B] FIG. 10 shows an example of the spectral response of the output of a quadrature transmitter TX after calibration. [Figure 6]FIG. 1 illustrates an example process according to an example embodiment. [Figure 7] FIG. 1 illustrates a functional block diagram of an example computer hardware platform that can be used to implement a specially configured computing device. DETAILED DESCRIPTION OF THE INVENTION

[0032] In the following detailed description, by way of example, numerous specific details are set forth in order to provide a thorough understanding of the relevant teachings. However, it will be understood that the present teachings may be practiced without such details. Additionally, well-known methods, procedures, components or circuits, or combinations thereof, have been described in a relatively general manner, omitting detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

[0033] The present disclosure relates generally to radar systems, and more particularly to a system and method for calibrating quadrature imbalance in frequency modulated continuous wave radar systems.

[0034] Quadrature imbalance in a transmitter or receiver can impair the ability to successfully transmit and / or receive the high-speed data carried by a radio signal. For example, quadrature imbalance can occur when the phase relationship between the I and Q channels is not exactly 90 degrees, or when the amplitude of the I channel differs from that of the Q channel, or both. Thus, quadrature imbalance can result from gain and / or phase mismatch of high-frequency components in the I and Q channels of an FMCW radar system. For example, the receiver components in the I channel may have slightly different phase and / or amplitude than the receiver components in the Q channel, thereby introducing imbalance or mismatch errors into the I and Q baseband signals. While these differences are typically small, such gain and phase imbalance can degrade the quality of an FMCW radar system, doubling its bandwidth and increasing the number of bit errors for a given data rate.

[0035] Known FMCW radar systems using quadrature architectures typically involve generating a frequency ramp in quadrature using a dual-channel direct digital synthesizer (DDS), which allows for a narrower 200 MHz bandwidth at up to 500 Msamples per second. Known architectures also typically require large bandwidths, are expensive to implement, and often require a field-programmable gate array (FPGA) to feed a dual-channel digital-to-analog converter (ADC) or an application-specific integrated circuit (ASIC) to feed two streams of data, resulting in high power consumption. However, such systems typically focus only on providing good dual-channel FMCW in quadrature and do not provide automatic image rejection calibration and monitoring. Poor image rejection results in signals being transmitted at the image frequency, which ultimately modulates the radar response.

[0036] The teachings herein can address quadrature imbalances in the receiver, transmitter, or both, which can facilitate the transmission and reception of high-speed data carried by wireless radar signals. Gain and / or undesired phase mismatch between the in-phase and quadrature paths is systematically removed through image rejection calibration. A quadrature FMCW signal is generated. Two radar measurements are received from a dual-channel analog-to-digital converter (ADC). A window signal is used to extract the in-phase and quadrature beat signals, sometimes referred to herein as Beat-I and Beat-Q. The two channels are correlated and repeated iteratively until the correlation between the Beat-I and Beat-Q signals is within a predetermined threshold or reaches maximum correlation. The concepts described herein allow for continuous verification and tracking of image rejection performance. No wired loop or external measurement equipment is required between the transmitter and receiver. Features of the present application can be better understood with reference to Figures 1 through 4, which are described in detail below.

[0037] 1 is a block diagram illustrating an architecture 100 for calibrating in-phase and quadrature path imbalance in a frequency modulated continuous wave (FMCW) radar system using a quadrature transceiver, according to an example embodiment. The architecture 100 includes a transceiver 108 having an in-phase input "I" and a quadrature input "Q" that are provided to a transmitter (TX) 110 of the quadrature transceiver 108. The quadrature transceiver 108 has a receiver (RX) 112 having an in-phase output "I" and a quadrature output "Q." In various embodiments, the transceiver can support various communication protocols that use OFDM signals, including, but not limited to, 802.11a / g / n (WiFi), 802.16d / e / m (WiMAX), and 3GPP Release 8 / 9 (LTE).

[0038] There is a dual channel FMCW signal generator 102 having a first output coupled to an in-phase input I of the transmitter 110 and a second output coupled to a quadrature input Q of the transmitter 110. The dual channel FMCW signal generator 102 receives a phase and amplitude input calibration signal (θ t ,A t ), the phase and amplitude are programmable based on the frequency ramp cycle 138. The dual channel FMCW signal generator 102 is configured to provide a window signal to the controller 140 that indicates the beginning and end of each frequency ramp cycle 138. For simplicity and to avoid clutter, various elements of the transmitter have been omitted, including the multiplexer, power supply, local oscillator, and digital signal processing (DSP) elements.

[0039] Because it is generated in the digital domain, the frequency ramp 138 generated by the dual-output FMCW signal generator 102 is digitally timed and synchronized using a common clock operating at 3.5 GHz, and any relative shifts between the two due to line delays and internal buffers are fixed, and therefore consistent and accurate. Such ramp generation is not affected by process variations, operating temperature, etc., to which analog circuit blocks are typically subject.

[0040] The outputs of the dual-output FMCW signal generator are in-phase and quadrature signals (TX IQ FMCW) represented by Equations 1 and 2 below.

[0041]

number

[0042]

number

[0043] where f0 is the starting frequency, T is the period, bw is the bandwidth, t is the time from the start of the ramp and is a value between 0 and T.

[0044] As previously mentioned, the dual-output FMCW signal generator 102 is programmable, allowing adjustment of the in-phase path, the quadrature path, or both. For example, Equation 3 below provides a calibration variable (θ t ,A t ) shows adjustable orthogonal paths based on

[0045]

number

[0046] As shown in Equation 3 above, the quadrature path includes a phase calibration variable θ that allows adjustment of the quadrature (and / or in-phase) signals provided to the transmitter 110 of the transceiver 108. t and the amplitude calibration variable A t For simplicity, the parameter A used in this specification t represent the relative amplitudes for the quadrature and in-phase paths. These calibration variables are provided as calibration variable signals by controller 140, as described in more detail below.

[0047] There is a first power splitter 104 coupled between a first output of the dual channel FMCW signal generator 102 and an in-phase input I of the transmitter 110. There is a second power splitter 106 coupled between a second output of the dual channel FMCW signal generator 102 and a quadrature Q input of the transmitter 110. The first and second power splitters 104 and 106 are two-way power splitters in that they each split the signal received from the output of the dual channel FMCW signal generator 102 and distribute it to a corresponding mixer 120 or 122 in the transmitter and receiver RX 112 feedback paths, respectively, as described in more detail below.

[0048] For example, the first splitter 104 is configured to receive the in-phase signal from the dual-output FMCW signal generator 102 and split it into two separate paths, one path leading to the in-phase input of the transmitter 110 of the quadrature transceiver 108 and the second path leading to the first mixer 120. When the image rejection of the in-phase and quadrature outputs of the receiver 112 is near perfect, the output of the receiver 112 (i.e., RX IQ FMCW) is given by Equation 4 and Equation 5, respectively.

[0049]

number

[0050]

number

[0051] Equations 4 and 5 above represent the RX IQ FMCW when image rejection is near perfect. For purposes of example only, and not limitation, a 1.4 GHz bandwidth using a 3.5 GSPS direct digital synthesizer (DDS) may be used as part of the dual-output FMCW signal generator 102. In one embodiment, two DDSs are used in the dual-output FMCW signal generator 102.

[0052] The first mixer 120 has a first input coupled to the second output of the first two-way splitter 104. It has a second input coupled to the in-phase output of the receiver 112. Similarly, the second mixer 122 has a first input coupled to the second output of the second two-way splitter 106 and a second input coupled to the quadrature output Q of the receiver 112. Each of the first and second mixers 120 and 122 provides an output that is supplied to a dual channel analog-to-digital converter 130.

[0053] The first mixer 120 mixes the split in-phase signal received from the first splitter 104 with the in-phase output I of the receiver 112. Similarly, the second mixer 122 mixes the split quadrature signal from the second splitter 106 with the quadrature output Q of the receiver 112. The outputs of both mixers 120 and 122 are provided to a dual-channel analog-to-digital converter 130 configured to output an in-phase beat signal (sometimes referred to herein as Beat-I) and a quadrature signal (sometimes referred to herein as Beat-Q). The dual-channel analog-to-digital converter 130 includes a first input coupled to the output of the first mixer 120 and a second input coupled to the output of the second mixer 122. The dual-channel ADC receives the signals from the mixers 120 and 122 and outputs corresponding in-phase and quadrature output signals, sometimes referred to herein as Beat-I and Beat-Q. In one embodiment, the teachings herein are compatible with the same relatively low-speed ADCs (e.g., 100 KPS to 10 MSPS) used in a typical radar pipeline, thereby reducing design complexity and cost. In some embodiments, there is a low-pass filter (not shown) at each input of the dual-channel ADC 130. Equations 6 and 7 show the unfiltered Beat-IQ FMCW signal, respectively.

[0054]

number

[0055]

number

[0056] Applying low-pass filtering (LPF) at the output of the dual-channel ADC 130 results in the following equation:

[0057]

number

[0058]

number

[0059] In one embodiment, the bandwidth provided at the output of the dual-channel ADC 130 is 100 KHz to 2 MHz. This relatively low frequency allows the use of a less complex and less costly ADC 130. The architecture includes a controller 140 coupled between the dual-channel FMCW signal generator 102 and the dual-channel ADC 130. In one embodiment, the controller 140 includes a quadrature calibration block 142 configured to receive an in-phase beat signal (Beat-I) from a first output of the dual-channel ADC and a quadrature beat signal (Beat-Q) from a second output of the dual-channel ADC 130. The controller 140 further includes a fast Fourier transform (FFT) block 144 configured to receive the quadrature beat signal from the second output of the dual-channel ADC and provide a radar output. The FFT block 144 is a practical implementation of the FMCW processing pipeline, enabling the system to detect reflections from various distances. Each single tone represents a response from a corresponding distance. Each bin step corresponds to a range resolution determined by the bandwidth. The quadrature calibration block 142 generates the phase and amplitude calibration signals (θ t ,A t ) is provided as an input to the dual FMCW signal generator 102.

[0060] Reference is now made to Figure 2, which illustrates a conceptual block diagram 200 of in-phase and quadrature imbalance calibration for an FMCW radar system, according to one exemplary embodiment. Note that many of the blocks in this diagram are the same as those in Figure 1, and therefore will not be repeated here for the sake of brevity. Additional details are provided in connection with the quadrature calibration block 142 of the controller 140, discussed above in the context of the description of Figure 1.

[0061] In block 240 of the quadrature calibration block 142, a predetermined path and calibration variable θ for phase calibration aret and A t In various embodiments, a table is provided having the following: t and A t Different techniques can be used to provide the calibration values ​​of . As non-limiting examples, a brute force approach may be used by filling in a table and selecting the option with the highest correlation value, a coarse-to-fine approach may be used by starting with a rough estimate (e.g., larger steps) and zooming in to more likely regions, a memory may be used to store previous values ​​and refine them to accommodate PVT variations, etc.

[0062] According to one example embodiment, the calibration value θ t and A t 3, which shows an example table 300 of paths used for the calibration variable θ t and A t It should be understood that other methods of generating Λ are also supported, and that table 300 is provided herein for illustrative purposes only and not for limitation.

[0063] θ from Table 300 until the threshold calibration is obtained. t and A t The horizontal axis 302 represents the phase values ​​θ t The vertical axis 304 represents the increment / decrement of the amplitude value A t For example, the initial calibration variable is denoted by Corr1 (θ t and A t ) = (0,1). In the next iteration, the variable (∂θ t, 1) is applied, and so on, until a desired threshold or maximum correlation between the in-phase and quadrature paths is achieved, denoted Beat-I and Beat-Q, as described in further detail below. While the snake method is shown, it should be understood that the present teachings are not limited thereto; other techniques can also be used (ask the inventors for different types of methods for implementing increment / decrement selection).

[0064] Referring back to FIG. 2, at block 242, the initial orthogonal calibration variables (θ t ,A t ) is used. As mentioned above, the initial correlation variables may be set to, for example, (0,1). These variables 252 are applied to the dual-output FMCW signal generator 102 to receive feedback from the feedback loop of the system of FIG.

[0065] In block 244, the Beat-I and Beat-Q outputs received from the dual-channel ADC 130 are used to correlate these two outputs (i.e., correlate the two beat signals Beat-I and Beat-Q). An example of this correlation is shown in Equation 10 below: M(θ t ,A t )=MAC(Beat-I,Beat-Q) / L (Equation 10) In the above equation, L is the length of the common correlation vector of Beat-I and Beat-Q.

[0066] One correlation is performed for each frequency ramp used to frequency modulate (FM) the FMCW radar system. In one embodiment, the DDS function of a digital ramp generator (DRG) is used. Ramp generation parameters allow the user to control both the rising and falling slopes of the ramp. The upper and lower boundaries of the ramp, as well as the step size and step rate of the rising portion of the ramp and the step size and step rate of the falling portion of the ramp, can all be programmable. Calibration is based on the similarity between the Beat-I and Beat-Q signals from the dual-channel DAC 130, as determined by a multiply and accumulate operation (MAC) of the "beat signals" Beat-I and Beat-Q performed by the quadrature calibration module 142.

[0067] A comparison is made at block 246 to determine if the correlation is within a predetermined threshold. Example equations are shown below in Equations 11 and 12. M(θ max ,A max ) <M(θ t ,A t ) (Equation 11) θ max ,A max =θ t ,A t (Formula 12)

[0068] For example, the above calculations can be used to adjust and verify that image rejection is optimal or within a predetermined threshold. To this end, the received radar responses in the I and Q paths, represented by the Beat-I and Beat-Q signals provided by the dual-channel ADC 130, are compared. For example, if the goal is to maximize the similarity of these signals to make them beat-matched, the correlation between the Beat-I and Beat-Q signals can be measured. A linear shift in the relative phase between the transmitted signals, starting from the conventional 90 degrees, can be applied.

[0069] If the threshold correlation is not achieved (i.e., "No" at decision block 248), the process returns to block 242, where the next pair of phase and amplitude calibration variables (e.g., from lookup table 300 of FIG. 3) is used, and the iterative process continues. For example, further iterations are performed incorporating amplitude and / or phase changes between the signals.

[0070] However, if the correlation is within a predetermined threshold (which may be a maximum threshold), then the appropriate orthogonal calibration variable (θ t ,A t ) pair is taken as the appropriate (e.g., maximum) variable 250 to be applied as the selected variable 252. This quadrature calibration can be applied to the in-phase path or the quadrature path in various embodiments. Therefore, a dual-channel programmable signal generator 102 is used to generate two signals in quadrature, where one path is adjusted relative to the other. The calibration is based on the similarity between Beat-I and Beat-Q. In this way, a more accurate correlation between these two paths is obtained.

[0071] Note that in situations where the environment is not conductive so that reflections are measured, beam steering can enhance the naturally occurring leakage 210 between TX 110 and RX 112 for calibration. When the radar response is weak (e.g., when the radar is pointed toward the sky), the phase at RX 112 and TX 110 can be set to increase crosstalk by forming an antenna-based loop that produces a strong radar response. For example, in one embodiment, the beam direction of TX 110 and / or RX 112 can be adjusted (e.g., by transmitting TX downward (i.e., toward RX) and / or adjusting receiver RX to sense up (e.g., in the direction of TX)) to account for leakage currents so that the calibration performance of system 200 can be evaluated.

[0072] Reference is now made to Figure 4, which shows a more detailed block diagram 400 of an architecture for calibrating in-phase and quadrature path imbalances in a frequency-modulated continuous wave radar system using quadrature transmitters and receivers, according to one exemplary embodiment. Many of the components in Figure 4 are similar to those in Figure 1, and therefore will not be described again for the sake of brevity. In the embodiment of Figure 4, the architecture illustrates how it can accommodate the use of two single-output DDSs.

[0073] Initially, both direct digital synthesizers (DDSs) are programmed with identical ramp parameters, such as ramp rate, step size, and bandwidth. The notable parameter difference from the embodiment in Figure 1 is that the one connected in phase generates a cosine wave, while the one connected in quadrature generates a sine wave.

[0074] As shown in Figure 4, a clock distribution integrated circuit (IC) 402 provides a reference clock to both DDSs 404 and 406, thereby avoiding the use of an internal phase-locked loop (PLL). In the architecture of Figure 4, two separate DDSs (i.e., 404 and 406) are used. In the embodiment of Figure 4, a divided clock of the DDS system clock results in synchronous control of the digital ramps of both DDSs 404 and 406.

[0075] The DDS outputs signals when the ramp starts and ends (DROVR) at 410 and 412 respectively. If the received signal is not strong enough, the controller steers TX 110 and RX 112 towards each other.

[0076] The ADC 130 receives the outputs of the mixers 120, 122 and has a digital input for a ramp signal that is synchronized with the two analog inputs. The controller 140 uses this ramp signal to clip both analog inputs for further calculation of the correlation value.

[0077] The teachings herein provide better image rejection between the TX 110 and the RX 112. In one aspect, verification of actual image rejection at low frequency signals is already available in the beat signals Beat-I and Beat-Q, eliminating the need for manual spectrum analyzers or dedicated circuitry at high frequencies. In one embodiment, the system of FIG. 2 provides continuous tracking of received signal quality via feedback provided by the Beat-I and Beat-Q signals evaluated by the quadrature calibration block 142.

[0078] Reference is now made to Figures 5A and 5B, which show the spectral response of the quadrature receiver RX output before and after calibration, respectively. As shown in Figure 5A, prior to system calibration, the initial I and Q were set to cosine and sine waves accordingly, thus resulting in no TX image suppression. In contrast, Figure 5B shows the system levels after calibration with proper amplitude and phase compensation based on the teachings herein so that the I and Q outputs are the same, thereby providing proper 25 dB TX image suppression.

[0079] With the overview of the example architectures 100, 200, and 400 outlined above, it may be helpful to now consider an overview of an example process. To that end, FIG. 6 illustrates a process 600 for an automatic image rejection method for a frequency-modulated continuous wave radar system, according to one example embodiment. Process 600 is illustrated as a collection of logic flow chart blocks, which represent sequences of operations that may be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer-executable instructions that, when executed by one or more processors of a controller, perform the described operations. Generally, computer-executable instructions may include routines, programs, objects, components, data structures, etc. that perform a function or implement an abstract data type. Within each process, the order in which the operations are described is not intended to be limiting, and any number of the described blocks may be combined in any order and / or executed in parallel to implement the process. For illustrative purposes, process 600 will be described with reference to architecture 100 of FIG. 1.

[0080] In block 602, a quadrature FMCW signal including an in-phase signal and a quadrature signal is generated by the dual-output FMCW signal generator 102.

[0081] At block 604, the in-phase and quadrature signals are transmitted by the transmitter TX 110 of the transceiver 108.

[0082] At block 606, radar measurements are received in response to the transmitted in-phase and quadrature signals of the transceiver 108, including returned in-phase and quadrature signals.

[0083] At block 608 , the response in-phase signal and the response quadrature signal are provided to a dual channel analog-to-digital converter (ADC) 130 .

[0084] At block 610, the controller 140 receives a window signal that indicates the beginning and end of a frequency ramp cycle for the generated quadrature FMCW signal.

[0085] In block 612, the controller 140 extracts an in-phase beat signal (Beat-I) and a quadrature beat signal (Beat-Q) from the dual-channel ADC 130 based on the receive window signal.

[0086] At block 614, the controller 140 correlates Beat-I with Beat-Q.

[0087] At block 616, it is determined whether the correlation is above a predetermined threshold. If so (i.e., "YES" at decision block 616), the controller proceeds to block 618 where the controller adjusts the phase calibration variable (θ t ) or amplitude calibration variable (A t ) or both as inputs to a dual output FMCW signal generator to set relative phase and / or amplitude adjustments.

[0088] If not (i.e., "NO" at decision block 616), the process proceeds to block 620 where the controller calculates a new phase calibration variable (θ t ) or a new amplitude calibration variable (A t ) or both as inputs to the dual output FMCW signal generator to determine new relative phase and / or amplitude adjustments. This iterative process then returns to block 602 and continues until the correlation exceeds a predetermined threshold.

[0089] As noted above, the functionality associated with automatic image rejection in a frequency modulated continuous wave radar system, such as that shown in Figures 1, 2, and 4, according to process 600 of Figure 6, may require a controller or processor. In this regard, Figure 7 illustrates an example functional block diagram of a computer hardware platform 700 that can be used to implement a specially configured computing device capable of implementing the controller of Figure 1.

[0090] The computer platform 700 may include a central processing unit (CPU) 704, a hard disk drive (HDD) 706, a random access memory (RAM) and / or read-only memory (ROM) 708, a keyboard 710, a mouse 712, a display 714, and a communication interface 716, which are connected to the system bus 702.

[0091] In one embodiment, the HDD 706 has functionality that includes storing programs capable of performing various processes, such as a quadrature calibration engine 740, as described herein. The quadrature calibration engine 740 can have various modules configured to perform various functions, such as those described in the context of FIG. 1 and other functions. For example, there may be an interaction module 742 that operates to interface with a dual channel ADC to extract the in-phase beat, the quadrature beat, or both. The appropriate quadrature calibration variables θ that are used as inputs to the dual output FMCW signal generator may be stored in the memory 704. t Or A t There may also be a calibration variable generation module 744 configured to generate the orthogonal calibration variables θ t Or A t Or both may be calculated or retrieved from a look-up table by following a snake pattern, as described herein.

[0092] In one embodiment, there is a digital filtering module that operates to low-pass filter the signal received from the dual channel ADC. There may also be an FFT module 748 that operates to provide a radar output based on the received quadrature beat signal from the dual channel ADC.

[0093] While modules 742-748 are shown in FIG. 7 as part of HDD 706, in some embodiments, one or more of these modules may be implemented in hardware in computing device 700. For example, the modules described herein may be implemented partly in hardware and partly in software. That is, one or more of the components of quadrature calibration engine 740 shown in FIG. 7 may be implemented in electronic circuitry including transistors, diodes, capacitors, resistors, inductors, varactors, or memristors, or combinations thereof. In other words, quadrature calibration engine 740 may be implemented with one or more specially designed electronic circuits that perform the specific tasks and functions described herein.

[0094] The description of various embodiments of the present teachings has been presented for illustrative purposes, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terms used herein have been selected to best explain the principles of the embodiments, practical applications, or technical improvements over commercially available technology, or to enable those skilled in the art to understand the embodiments disclosed herein.

[0095] While the foregoing describes what are considered to be best mode and / or alternative embodiments, it should be understood that various modifications thereof are possible, that the subject matter disclosed herein can be implemented in a variety of forms and embodiments, and that the teachings are applicable to many applications, only some of which are described herein. It is intended by the following claims to claim all such applications, modifications, and variations that fall within the true scope of the present teachings.

[0096] The components, steps, features, objects, advantages, and benefits described herein are exemplary only. None of them, nor any discussion thereof, are intended to limit the scope of patent protection. While various advantages have been described herein, it should be understood that not all embodiments necessarily include all advantages. Unless otherwise specified, all measurements, values, ratings, positions, dimensions, sizes, and other specifications described herein, including the following claims, are approximate and not precise. They are intended to have a reasonable range consistent with the functions to which they pertain and what is customary in the technical field to which they pertain.

[0097] Many other embodiments are contemplated, including those with fewer, additional, or different components, steps, features, objects, advantages, and / or combinations thereof. These include those with different arrangements and / or orderings of components and / or steps. For example, any of the signals described herein may be scaled, buffered, scaled and buffered, converted to another state (e.g., voltage, current, charge, time, etc.), or converted between other states (e.g., high to low and low to high) without substantially altering the underlying control method.

[0098] Aspects of the present disclosure are described herein with reference to flowchart illustrations and / or block diagrams that illustrate methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0099] These computer-readable program instructions may be supplied to a processor of a general-purpose computer, special-purpose computer, or other programmable data processing apparatus to implement a machine in which the instructions, executed by the processor of the computer or other programmable data processing apparatus, form means for implementing the functions / acts specified in the blocks of the flowcharts and / or block diagrams. These computer-readable program instructions may be stored on a computer-readable storage medium capable of instructing a computer, programmable data processing apparatus, or other apparatus, or combination thereof, to function in a particular manner, such that the computer-readable storage medium on which the instructions are stored comprises an article of manufacture containing instructions that implement aspects of the functions / acts specified in the blocks of the flowcharts and / or block diagrams.

[0100] The computer readable program instructions may be loaded into a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other device to realize a computer-implemented process, such that the instructions, which execute on the computer, other programmable apparatus, or other device, implement the functions / acts specified in the blocks of the flowchart and / or block diagram.

[0101] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of instructions, including one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may in fact be executed substantially in parallel, or the blocks may possibly be executed in the reverse order, depending on the functionality involved. It should also be noted that each block of the block diagrams and / or flowchart diagrams, and combinations of blocks in the block diagrams and / or flowchart diagrams, may be implemented by a dedicated hardware-based system that performs the specified functions or operations or that implements a combination of dedicated hardware and computer instructions.

[0102] While the above has been described in conjunction with exemplary embodiments, it should be understood that the term "exemplary" means only an example, not best or optimal. Except as immediately described, nothing described or shown is intended to, and should not be construed as, providing to the public any components, steps, features, objects, advantages, benefits, or equivalents, whether claimed or not.

[0103] Terms and phrases used herein should be understood to have the ordinary meanings given to such terms and phrases with respect to their respective fields of inquiry and study, unless a specific meaning is otherwise stated herein. Relative terms such as first and second may be used solely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between the entities or operations. The terms "comprises," "comprising," or other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes recited elements may include not only those elements, but also other elements not expressly recited or inherent in such process, method, article, or apparatus. An element preceded by "a" or "an" does not, without further constraints, exclude the presence of additional identical elements in a process, method, article, or apparatus that includes the element.

[0104] The Abstract is provided to allow the reader to quickly grasp the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Furthermore, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Instead, as the following claims reflect, inventive subject matter lies in some, but not all, features of a single disclosed embodiment. Accordingly, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as separately claimed subject matter.

Claims

1. 1. A frequency modulated continuous wave (FMCW) radar system comprising: a quadrature transceiver including a transmitter having an in-phase input and a quadrature input, and a receiver having an in-phase output and a quadrature output; a dual channel FMCW signal generator including a first output coupled to the in-phase input of the transmitter and a second output coupled to the quadrature input of the transmitter; a first splitter coupled between the first output of the dual channel FMCW signal generator and the in-phase input of the transmitter; a second splitter coupled between the second output of the dual channel FMCW signal generator and the quadrature input of the transmitter; a first mixer including a first input coupled to the second output of the first splitter, a second input coupled to the in-phase output of the receiver, and an output; a second mixer including a first input coupled to a second output of the second splitter, a second input coupled to the quadrature output of the receiver, and an output; a dual-channel analog-to-digital converter (ADC) including a first input coupled to the output of the first mixer and a second input coupled to the output of the second mixer; a controller coupled between the dual-channel FMCW signal generator and the dual-channel ADC; 1. An FMCW radar system comprising:

2. 2. The FMCW radar system of claim 1, wherein the dual channel FMCW signal generator is programmable.

3. 3. An FMCW radar system according to claim 1, wherein the dual channel FMCW signal generator is configured to provide a window signal indicating the start and end of each frequency ramp cycle.

4. 4. The FMCW radar system of claim 1, wherein the controller includes a quadrature calibration block configured to receive an in-phase beat signal from a first output of the dual-channel ADC and a quadrature beat signal from a second output of the dual-channel ADC.

5. 5. The FMCW radar system of claim 4, wherein the controller further comprises a fast Fourier transform (FFT) block configured to receive the quadrature beat signal from the second output of the dual-channel ADC and to provide a radar output having an improved signal-to-noise ratio (SNR).

6. The quadrature calibration block calculates the phase calibration variable (θ ｔ ) or amplitude calibration variable (A ｔ 5. The FMCW radar system of claim 4, wherein the FMCW radar system is configured to provide at least one of the following as an input to the dual channel FMCW signal generator:

7. 7. The FMCW radar system of claim 1, further comprising a low-pass filter in each input channel of the dual-channel ADC.

8. 8. The FMCW radar system according to claim 1, wherein the dual-channel FMCW signal generator is a digital circuit block.

9. The controller: The initial orthogonal calibration variables (θ ｔ , A ｔ ), and The initial orthogonal calibration variables (θ ｔ , A ｔ ) as an input to said dual channel FMCW signal generator; The initial orthogonal calibration variables (θ ｔ , A ｔ receiving an in-phase beat signal from a first output of the dual-channel ADC and a quadrature beat signal from a second output of the dual-channel ADC based on correlating the in-phase beat signal with the quadrature beat signal; Upon determining that the correlation is less than a predetermined threshold, new quadrature calibration variables (θ ｔ , A ｔ ) 9. The FMCW radar system according to claim 1, wherein the FMCW radar system is configured as follows:

10. 1. A method for automatic image rejection in a frequency modulated continuous wave (FMCW) radar system, comprising: generating a quadrature FMCW signal including an in-phase signal and a quadrature signal by a dual-output FMCW signal generator; transmitting the in-phase signal and the quadrature signal by a transmitter of a transceiver; receiving a radar signal including a responsive in-phase signal and a responsive quadrature signal in response to the transmitted in-phase signal and the quadrature signal from the transceiver; providing the responsive in-phase signal and the responsive quadrature signal to a dual channel analog-to-digital converter (ADC); receiving, by a controller, a window signal indicating a start and an end of a frequency ramp cycle of the generated quadrature FMCW signal; extracting, by a controller, an in-phase beat signal (Beat-I) and a quadrature beat signal (Beat-Q) from the dual-channel ADC based on the received window signal; correlating the Beat-I with the Beat-Q by the controller; The controller calculates a phase calibration variable (θ ｔ ) or amplitude calibration variable (A ｔ ) or both as inputs to said dual output FMCW signal generator to generate relative phase and / or amplitude adjustments; A method comprising:

11. If it is determined that the threshold correlation has not been reached, the phase calibration variable (θ) is used as an input to the dual output FMCW signal generator until the threshold correlation is reached. ｔ ) or the amplitude calibration variable (A ｔ 11. The method of claim 10, further comprising iteratively adjusting the .times. ...

12. splitting the in-phase signal of the quadrature FMCW signal by a first power splitter into a first in-phase signal of the quadrature FMCW signal provided to the transmitter and a second in-phase signal of the quadrature FMCW signal as a first in-phase input to a first mixer; splitting the quadrature signal of the quadrature FMCW signal by a second power splitter into a first quadrature signal of the quadrature FMCW signal provided to the transmitter and a second quadrature signal of the quadrature FMCW signal as a first quadrature input to a second mixer; 12. The method of claim 10 or 11, further comprising:

13. mixing, by the first mixer, the first in-phase input with an in-phase radar signal received by a receiver of the transceiver and providing the result as a first input to a dual-channel analog-to-digital converter (ADC); mixing, by the second mixer, the first quadrature input with a quadrature radar signal received by the receiver and providing the result as a second input to the dual channel ADC; The method of claim 12 further comprising:

14. 13. The method of claim 10, further comprising adjusting at least one of the transmitter orientation or the receiver orientation of the transceiver to increase signal reflections to enhance calibration capabilities of the FMCW radar system.

15. 1. A method for calibrating a frequency modulated continuous wave (FMCW) radar system, comprising: providing a quadrature transceiver including a transmitter having an in-phase input and a quadrature input, and a receiver having an in-phase output and a quadrature output; providing a dual channel FMCW signal generator including a first output coupled to the in-phase input of the transmitter and a second output coupled to the quadrature input of the transmitter; coupling a first splitter between the first output of the dual channel FMCW signal generator and the in-phase input of the transmitter; coupling a second splitter between the second output of the dual channel FMCW signal generator and the quadrature input of the transmitter; providing a first mixer including a first input coupled to a second output of the first splitter, a second input coupled to the in-phase output of the receiver, and an output; providing a second mixer including a first input coupled to a second output of the second splitter, a second input coupled to the quadrature output of the receiver, and an output; providing a dual channel analog-to-digital converter (ADC) including a first input coupled to the output of the first mixer and a second input coupled to the output of the second mixer; coupling a controller between the dual channel FMCW signal generator and the dual channel ADC; A method comprising:

16. The dual channel FMCW signal generator generates a phase calibration variable (θ ｔ ) or amplitude calibration variable (A ｔ ) or both; The received phase calibration variable (θ ｔ ) or the amplitude calibration variable (A ｔ ) or both of said dual channel FMCW signal generators; 16. The method of claim 15, further comprising:

17. A computer-readable storage medium storing computer-executable instructions for causing a computer to execute the method according to any one of claims 10 to 14.

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