Interference-canceling RF receiver circuit, corresponding system, radar sensor system, vehicle and method

Abstract

An input receives a radio frequency (RF) signal having an interfering component superimposed thereon. The RF signal is mixed with a local oscillator (LO) signal and down-converted to an intermediate frequency (IF) to generate a mixed signal which includes a frequency down-converted interfering component. The mixed signal is amplified by an amplifier to generate an output signal. A feedback loop processes the output signal to generate a correction signal for cancelling the frequency down-converted interfering component at the input of the amplifier. The feedback loop includes a low-pass filter and a amplification circuit which outputs the correction signal.

Claims

1. A radio frequency (RF) receiver circuit, comprising: an RF input port; an input network configured to receive an RF signal from said RF input port and to provide an RF current signal, said RF signal having an interfering component superimposed thereon; a mixer circuit, comprising a signal input, a local oscillator (LO) input and an intermediate frequency (IF) output and configured to: a) receive said RF current signal at said signal input; b) receive a LO signal at said LO input; and c) provide a mixed signal at said IF output; wherein the mixed signal comprises a frequency down-converted interfering component; an interference-canceling loop configured to provide at an output a corrected IF signal, wherein the interference-canceling loop comprises: an amplifier circuit having an input coupled to said IF output of the mixer circuit and an output; and a feedback network configured to generate a compensation current for application to the mixed signal at the input of said amplifier circuit as a function of the signal at the output of said amplifier circuit, thereby removing said frequency down-converted interfering component in said mixed signal.

2. The RF receiver circuit of claim 1, wherein the feedback network comprises a trans-conductance amplifier circuit and a low-pass filter stage, the trans-conductance amplifier having input nodes coupled to said output through said low-pass filter stage.

3. The RF receiver circuit of claim 2, wherein the amplifier circuit comprises a trans-impedance amplifier having: input nodes coupled to the mixer IF output; and output nodes coupled to said input nodes of the feedback network.

4. The RF receiver circuit of claim 1, wherein: the input network comprises an impedance matched voltage-to-current converter network; and the mixer circuit comprises a passive mixer.

5. The RF receiver circuit of claim 4, wherein the passive mixer comprises a switch quad type mixer of a passive Gilbert-cell type.

6. The RF receiver circuit of claim 1, further comprising: at least one antenna coupled to the RF input port; and a local oscillator configured to generate the LO signal.

7. The RF receiver circuit of claim 1, wherein the RF receiver circuit is a component of a vehicular radar sensor system.

8. The RF receiver circuit of claim 7, wherein vehicular radar sensor system is a component of a vehicle.

9. A method, comprising: receiving a radio frequency (RF) signal having an interfering component superimposed thereon, wherein receiving the RF signal comprises receiving the RF signal as a voltage signal and converting said voltage signal to a current signal; receiving a local oscillator (LO) signal generated by an oscillator; signal mixing said RF signal and said LO signal to generate a mixed signal comprising a frequency down-converted intermediate frequency (IF) interfering component; amplifying said mixed signal in a feedback loop; applying an interference-canceling feedback signal generated by said feedback loop to the mixed signal before amplifying, thereby removing said IF interfering component in said mixed signal; and outputting a corrected IF signal to user stages.

10. The method of claim 9, wherein receiving the RF signal comprises applying impedance matching.

11. A circuit, comprising: a mixing circuit having a signal input configured to receive a radio frequency (RF) signal which includes a superimposed interfering component, a local oscillator (LO) input configured to receive a LO signal and a signal output generating a downconverted signal at an intermediate frequency (IF) which includes an IF interfering component; a trans-impedance amplifier having an input configured to receive the downconverted signal with the IF interfering component and an output configured to generate an amplified IF output signal; a filter circuit having an input configured to receive the amplified IF output signal; and a trans-conductance amplifier circuit having an input configured to receive a filtered signal output from the filter circuit and an output configured to apply a cancellation signal to the downconverted signal at the input of the trans-impedance amplifier which cancels the IF interfering component present within the downconverted signal.

12. The circuit of claim 11, wherein the low-pass filter is configured to pass frequencies which include a frequency of the IF interfering component.

13. The circuit of claim 11, wherein the mixing circuit comprises a switch quad type mixer of a passive Gilbert-cell type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more embodiments will now be described, by way of non-limiting example only, with reference to the annexed Figures, wherein:

(2) FIG. 1A shows a vehicle equipped with a radar sensor to detect an object;

(3) FIG. 1B is an exemplary block diagram of a radar sensor;

(4) FIG. 2A illustrates a parasitic leakage concern with the sensor of FIG. 1A;

(5) FIG. 2B is a frequency diagram;

(6) FIG. 3 is an exemplary diagram of one or more embodiments of a RF receiver circuit;

(7) FIG. 4 is an exemplary diagram of details of the RF receiver circuit of FIG. 3;

(8) FIG. 5 is an exemplary diagram of principles underlying embodiments of FIG. 4,

(9) FIG. 6 is an exemplary diagram of a radar system and a vehicle.

DETAILED DESCRIPTION

(10) In the ensuing description, one or more specific details are illustrated, aimed at providing an in-depth understanding of examples of embodiments of this description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that certain aspects of embodiments will not be obscured.

(11) Reference to “an embodiment” or “one embodiment” in the framework of the present description is intended to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as “in an embodiment” or “in one embodiment” that may be present in one or more points of the present description do not necessarily refer to one and the same embodiment.

(12) Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.

(13) The references used herein are provided merely for convenience and hence do not define the extent of protection or the scope of the embodiments.

(14) FIG. 3 is exemplary of a radio frequency to intermediate frequency (RF-to-IF) converter circuit 30 architecture according to one or more embodiments.

(15) In one or more embodiments, the down-converter circuit 30 may comprise: an input network 32, configured to receive an RF signal V.sub.RF at an RF input port and to provide an RF current signal I.sub.RF, e.g., a voltage-to-current (V2I) converter circuit, configured to receive and propagate an RF signal, e.g., a voltage signal V.sub.RF; the RF signal V.sub.RF may have an interfering component V.sub.L, e.g., generated by leakage in an antenna 20, 22 or by spurious signals in the environment surrounding the component, superimposed to an echo signal component V.sub.R, e.g., V.sub.RF=V.sub.R+V.sub.L where V.sub.L is a voltage associated to leakage, as discussed in the foregoing; a mixer stage 34, e.g., a three-port network circuit block configured to receive the RF signal I.sub.RF and a local oscillator signal, e.g., a voltage signal V.sub.LO, at respective input ports, and provide at an output port a mixed signal I.sub.IF, wherein the mixed signal I.sub.IF is a frequency down-converted version of the RF signal I.sub.RF, e.g., resulting from signal multiplication I.sub.IF=I.sub.RF*f(V.sub.LO); a interference-canceling feedback loop 36, 38 comprising an active load such as an amplifier circuit (Amp) 36 and a, e.g., retroactive, compensation (Comp) stage 38, coupled at the mixer output port, comprising circuitry configured to receive and amplify the mixed signal I.sub.IF and to remove therefrom, e.g. by negative feedback loop compensation, a leaked interfering component of the signal.

(16) In one or more embodiments, the compensation stage is coupled across the active load 36, so as to provide as an output of the active load a compensated IF signal, the compensated IF signal having compensated said IF interfering component in said mixed signal.

(17) In one or more embodiments, inventors have observed that working with a RF current signal in place of a RF voltage signal may improve linearity performance of the down-converter 30.

(18) In one or more embodiments, the absence of a low-noise amplifier circuit block may improve linearity performance of the down-converter 30.

(19) FIG. 4 is exemplary of one or more embodiments of the down-converter circuit arrangement 30.

(20) In one or more embodiments, the input network 32 may comprise, as exemplified in FIG. 4: a first transformer T.sub.1, comprising a first primary winding branch T.sub.11 and a first secondary winding branch T.sub.12, a differential stage 324, comprising a first and a second transistor Q.sub.1, Q.sub.2, for instance a pair of MOSFET transistors in a common-source configuration having first control terminal coupled to a node of first secondary winding T.sub.12 in the first transformer T.sub.1 and a second control terminal coupled to a second node of the first secondary winding T.sub.12 in the first transformer T.sub.1, for instance first Q.sub.1 and second Q.sub.2 transistor control terminals coupled across the first secondary winding T.sub.12 in the first transformer T.sub.1, and a second transformer stage T.sub.2, comprising a second primary winding branch T.sub.21 and a second secondary winding branch T.sub.22.

(21) In one or more embodiments, a first capacitor may be coupled between output terminals of the first and second transistors Q.sub.1, Q.sub.2 while a second capacitor C.sub.2 may be coupled across the second secondary winding T.sub.22 in the second transformer T.sub.2.

(22) The input network 32, as mentioned, operates substantially as a voltage-to-current converter, from a voltage RF signal output by the receiver antenna to a current RF signal.

(23) Such a voltage-to-current converter may be obtained employing the differential stage 324, e.g., with the differential pair of transistors Q1, Q2 in a common gate configuration, designed to facilitate obtaining an impedance matching, e.g., a 50 Ohm matching, and a low noise figure.

(24) In one or more embodiments, the first secondary winding T.sub.12 is coupled to control terminals of the first and second transistor Q1, Q2 in the differential stage 324. The differential stage 324 provides a 50 Ohm input thus showing a low impedance to the input node.

(25) Such an input network arrangement 32 may facilitate avoiding saturation in the down-converter circuit 30: in fact, since the interfering component I.sub.L has a high value with respect to the RF signal value, closing the converter 32 on a high load may saturate the down-converter. Such a problem is hardly avoidable with the customary employ of a Low Noise Amplifier stage to receive the RF signal V.sub.RF, since LNA has a high load in order to provide a high gain.

(26) Conversely, such a linearity constraint problem may be solved employing a low impedance provided by virtual ground of the trans-impedance amplifier, as discussed herein.

(27) In one or more embodiments, the mixer stage 34 may comprise a passive mixer circuit block, wherein the output mixed signal I.sub.F has a lower power than the input signals V.sub.LO, I.sub.RF. Specifically, the mixer stage 34 may comprise a switch quad, e.g., a passive mixer based on a Gilbert-cell known per se. For instance, the passive mixer 34 may advantageously achieve a low noise figure (NF), specifically reduced IF flicker noise.

(28) In one or more embodiments, the amplifier circuit 36 may comprise a Trans-Impedance Amplifier (TIA) comprising: a differential stage 360, for instance an operational amplifier having a non-inverting input node 360a, an inverting input node 360b, an inverting output node 360c and a non-inverting output node 360d, wherein the input nodes 360a, 360b are at virtual ground, a first resistive branch R.sub.A coupled to the non-inverting input 360a and to the inverting output 360c, a second resistive branch R.sub.B coupled to the inverting input 360b and to the non-inverting output 360d.

(29) In an exemplary embodiment according to FIG. 4, the resistive branches R.sub.A and R.sub.B may have the same value of resistance, e.g., R.sub.A=R.sub.B=R.

(30) In one or more embodiments, the differential stage may be coupled to a Common Mode Feedback Circuit (CMFC) stage 362, known per se.

(31) In one or more embodiments, an output voltage V.sub.OUT is sensed across the output nodes 360c, 360d of the trans-impedance amplifier differential stage 360.

(32) In one or more embodiments, the feedback network 38 may comprise a trans-conductance amplifier 380 and a low-pass filter LPg, for instance a low-pass filter configured to preserve the IF signal component related to the echo signal to be detected.

(33) For instance, the low-pass filter LPg may be coupled between the output of the amplifier 36 and the input 380a, 380b of the transconductance amplifier 380 and may comprise a first resistance R.sub.gA, a second resistance R.sub.gB and a capacitor C.sub.g coupled between input nodes 380a, 380b of the transconductance amplifier 380.

(34) In one or more embodiments, the trans-conductance amplifier 380 may comprise: a non-inverting input node 380a, coupled via a first resistance R.sub.gA to the non-inverting output node 360d in the trans-impedance amplifier 360, an inverting input node 380b, coupled via a second resistance R.sub.gB to the inverting output node 360c in the trans-impedance amplifier 360, a first output node 380c, coupled to the inverting input 360b in the trans-conductance amplifier 360, and a second output node 380d, coupled to the non-inverting input node 360a in the trans-impedance amplifier 360.

(35) FIG. 5 is exemplary of operating principle underlying one or more embodiments of the down-converted circuit 30 as exemplified in FIG. 4.

(36) Unless otherwise discussed in the following, in FIG. 5 parts or elements like parts or elements already discussed in the foregoing are indicated with like reference/numerals, so that a corresponding detailed description will not be repeated here for brevity.

(37) As mentioned, the first primary winding branch T.sub.11 in the first transformer T.sub.1 the input network 32, receives an RF voltage signal V.sub.RF comprising a leaked interfering component V.sub.L superimposed to a signal V.sub.R, e.g., an echo signal received in a radar sensor, which may be expressed as V.sub.RF=V.sub.R+V.sub.L.

(38) As a result of the voltage-to-current conversion in the input network 32, the second transformer T.sub.2 may provide across its second secondary winding T.sub.22 a current I.sub.RF which may also comprise an equivalent leaked interfering component I.sub.L superimposed to a signal I.sub.R, which may be expressed as I.sub.RF=I.sub.R+I.sub.L.

(39) Such a current signal I.sub.RF, e.g., converted from the voltage RF signal V.sub.RF, may be multiplied in the mixer stage 34 with the signal V.sub.LO from the local oscillator (LO), hence providing a down-converted IF current signal i.sub.IF which comprises a down-converted leaked interfering component i.sub.L superimposed to a down-converted signal component i.sub.R, which may be expressed as i.sub.IF=i.sub.R+i.sub.L. At this point, the active load 36 and the compensation circuit 38, as a result of their feedback arrangement, may operate in an equivalent way to each receiving a component in the IF signal: specifically, the trans-impedance amplifier 360 in the active-load stage 36 may receive the signal component i.sub.R while the trans-conductance amplifier 380 may receive the down-converted leakage interfering component i.sub.L.

(40) In one or more embodiments, the transconductance amplifier 380 and the low-pass filter LPg may be configured to self-cancel the interfering component i.sub.L, e.g. by filtering and compensating.

(41) At the same time, the trans-impedance amplifier 360 may convert the current signal i.sub.R to a voltage signal hence providing a voltage output signal V.sub.OUT in the IF frequency range, hence frequency down-converted from RF, without any interfering component due to leakage/cross-talk in the antenna.

(42) FIG. 6 is exemplary of a vehicle V which may be equipped with at least one radar sensor system 100 comprising: a TX/RX antenna 20, 22 such as, for instance, a set of patch-array antennas, and at least one RF receiver circuit 30, providing a robust and accurate object-detection system and method, increasing road safety.

(43) In one or more embodiments the system 100 may further comprise further processing stages 200 and communication interfaces 500 and a battery 400 to provide power supply circuits in the system 100.

(44) For instance, the radar sensor system 100 in the vehicle V may provide support to a vehicle driver, e.g., via an Automated Driving Assistance System ADAS capable to take control over the vehicle, in detecting people passing on zebra-crossings during the night or in adverse eye visibility conditions, hence facilitating to reduce road accidents.

(45) It will be otherwise understood that the various individual implementing options exemplified throughout the figures accompanying this description are not necessarily intended to be adopted in the same combinations exemplified in the figures. One or more embodiments may thus adopt these (otherwise non-mandatory) options individually and/or in different combinations with respect to the combination exemplified in the accompanying figures.

(46) Without prejudice to the underlying principles, the details and embodiments may vary, even significantly, with respect to what has been described by way of example only, without departing from the extent of protection. The extent of protection is defined by the annexed claims.

(47) The claims are an integral part of the technical teaching provided herein with reference to the embodiments.