US-12621018-B2 - Configurable filter for subharmonic blockers in multiband wireless receivers

US12621018B2US 12621018 B2US12621018 B2US 12621018B2US-12621018-B2

Abstract

According to an aspect, there is provided a tunable radio frequency filter ( 209 ) for preselection in a multiband radio receiver or transceiver with a low-noise amplifier with a single-ended input. The tunable radio frequency filter comprises a first capacitor (C 1 , 1001 ) having a first terminal for connecting to at least one antenna of the multiband radio receiver or transceiver and a second terminal; and a series resonant circuit, connected between the second terminal of the first capacitor and the ground. The series resonant circuit comprises a first inductor (L 1 1003 ) and a tunable capacitor (C t , 1004 ) connected in series with first inductor and having a plurality of tuning values corresponding to operating frequency bands of the multiband radio receiver or transceiver. The tunable capacitor is implemented in an integrated circuit. The series resonant circuit is configured to be resonant at a plurality of first subharmonics of frequencies of the operating frequency bands. Optionally the filter comprises a second capacitor (C2, 1002 ) and a second inductor (L2, 1010 ) in series between the resonant circuit to ground and the input of the LNA. The second inductor adds to impedance matching and low pass filtering above the operating frequency bands.

Inventors

Pete Sivonen
Jarkko Jussila

Assignees

NORDIC SEMICONDUCTOR ASA

Dates

Publication Date: 20260505
Application Date: 20220311
Priority Date: 20210315

Claims (12)

1 . A multiband radio receiver or transceiver comprising: at least one low-noise amplifier having, respectively, at least one single-ended input; at least one tunable radio frequency filter for preselection in the multiband radio receiver or transceiver, each of the at least one tunable radio frequency filter comprising: a first capacitor having a first terminal for connecting to at least one antenna of the multiband radio receiver or transceiver and a second terminal; a second capacitor connected, via a first terminal of the second capacitor, to the second terminal of the first capacitor and, via a second terminal of the second capacitor, to a single-ended input of the at least one low-noise amplifier; and a series resonant circuit, connected between the second terminal of the first capacitor and the ground, comprising a first inductor and a tunable capacitor connected in series with first inductor and having a plurality of tuning capacitance values corresponding to operating frequency bands of the multiband radio receiver or transceiver, wherein the tunable capacitor is implemented in an integrated circuit, the series resonant circuit being configured to be resonant at a plurality of first subharmonics of frequencies of the operating frequency bands when the tunable capacitor is set to the plurality of tuning capacitance values, respectively, a first subharmonic of a given frequency being a frequency equal to said given frequency divided by two.
2 . The multiband radio receiver or transceiver according to claim 1 , wherein, for each of the at least one tunable radio frequency filter, the series resonant circuit is configured to be resonant at a plurality of first subharmonics of substantially central frequencies of the operating frequency bands of the multiband radio receiver or transceiver when the tunable capacitor is set to the plurality of tuning capacitance values, respectively.
3 . The multiband radio receiver or transceiver according to claim 1 , wherein, for each of the at least one tunable radio frequency filter, the first capacitor, the second capacitor and the first inductor are non-tunable off-chip circuit elements, the first capacitor and the first inductor are non-tunable off-chip circuit elements and the second capacitor is a non-tunable circuit element implemented in the integrated circuit or the first inductor is a non-tunable off-chip circuit element and the first and second capacitors are a non-tunable circuit elements implemented in the integrated circuit.
4 . The multiband radio receiver or transceiver according to claim 1 , wherein, for each of the at least one tunable radio frequency filter, the first and second capacitors have different capacitance values.
5 . The multiband radio receiver or transceiver according to claim 1 , wherein, for each of the at least one tunable radio frequency filter, values of the first capacitor, the second capacitor and the first inductor and the plurality of tuning capacitance values of the tunable capacitor have been selected for optimizing impedance matching to an input impedance of an associated low-noise amplifier of the multiband radio receiver or transceiver over the operating frequency bands of the multiband radio receiver or transceiver while maintaining attenuation at the first subharmonics and second subharmonics of said frequencies of the operating frequency bands above respective pre-defined levels when corresponding ones of the plurality of tuning values are used for the tunable capacitor, a second subharmonic of a given frequency being a frequency equal to said given frequency divided by three.
6 . The multiband radio receiver or transceiver according to claim 1 , wherein, for each of the at least one tunable radio frequency filter, values of the first capacitor, the second capacitor and the first inductor and the plurality of tuning capacitance values of the tunable capacitor have been selected for maximizing attenuation at the first subharmonics and second subharmonics of said frequencies of the operating frequency bands when corresponding ones of the plurality of tuning capacitance values are used for the tunable capacitor while maintaining impedance matching to an input impedance of an associated low-noise amplifier of the multiband radio receiver or transceiver as quantified by an s 11 parameter over the operating frequency bands of the multiband radio receiver or transceiver below a pre-defined level, a second subharmonic of a given frequency being a frequency equal to said given frequency divided by three.
7 . The multiband radio receiver or transceiver according claim 1 , wherein in each of the at least one tunable radio frequency filter, the tunable capacitor is implemented as a capacitor matrix.
8 . The multiband radio receiver or transceiver according to claim 1 , wherein each of the at least one tunable radio frequency filter further comprises: a second inductor connected in series with the second capacitor for providing low-pass filtering at frequencies above the operating frequency bands of the radio receiver or transceiver.
9 . The multiband radio receiver or transceiver according to claim 1 , wherein said at least one tunable radio frequency filter consists of a single tunable radio frequency filter being the only preselection filter of the multiband radio receiver or transceiver.
10 . The multiband radio receiver or transceiver according to claim 1 , wherein said at least one low-noise amplifier comprises a first low-noise amplifier with a first single-ended input configured to operate at a first frequency range and a second low-noise amplifier with a second single-ended input configured to operate at a second frequency range different from the first frequency range; and said at least one tunable radio frequency filter comprises a first tunable radio frequency filter preceding the first low-noise amplifier and configured to operate at a first plurality of frequency bands covering, at least in part, the first frequency range and a second tunable radio frequency filter preceding the second low-noise amplifier and configured to operate at a second plurality of frequency bands covering, at least in part, the second frequency range.
11 . The multiband radio receiver or transceiver of claim 10 , further comprising: switching means for switching between reception via the first tunable radio frequency filter and the first single-ended low-noise amplifier and via the second tunable radio frequency filter and the second single-ended low-noise amplifier.
12 . A multiband radio receiver or transceiver, comprising: a low-noise amplifier with a differential input comprising an inverting input and a non-inverting input; a differential tunable radio frequency filter acting as a non-band-specific preselection filter of the multiband radio receiver or transceiver, the differential tunable radio frequency filter comprising: a pair of tunable radio frequency filters comprising a first tunable radio frequency filter for connecting to the non-inverting input of the differential low-noise amplifier and a second tunable radio frequency filter for connecting to the inverting input of the differential low-noise amplifier, wherein each of the at least one tunable radio frequency filter comprises: a first capacitor having a first terminal for connecting to at least one antenna of the multiband radio receiver or transceiver and a second terminal; a second capacitor connected, via a first terminal of the second capacitor, to the second terminal of the first capacitor and, via a second terminal of the second capacitor, to the differential input of the low-noise amplifier; and a series resonant circuit, connected between the second terminal of the first capacitor and the ground, comprising a first inductor and a tunable capacitor connected in series with first inductor and having a plurality of tuning capacitance values corresponding to operating frequency bands of the multiband radio receiver or transceiver, wherein the tunable capacitor is implemented in an integrated circuit, the series resonant circuit being configured to be resonant at a plurality of first subharmonics of frequencies of the operating frequency bands when the tunable capacitor is set to the plurality of tuning capacitance values, respectively, a first subharmonic of a given frequency being a frequency equal to said given frequency divided by two.

Description

This application is the U.S. national phase of International Application No. PCT/EP2022/056301 filed Mar. 11, 2022, which designated the U.S. and claims priority to FI patent application No. 20215279 filed Mar. 15, 2021, the entire contents of each of which are hereby incorporated by reference. TECHNICAL FIELD Various example embodiments relate to RF filters for radio receivers and transceivers. BACKGROUND Integrated radio frequency (RF) receivers and transceivers are extensively employed in wireless communication devices such as in cellular phones, tablets, and Internet of things (IoT) machines. As modern wireless devices usually operate at multiple frequency bands and they support many wireless standards, the corresponding radio frequency integrated circuits (RFICs) need to provide multiband and multimode operation. In general, a separate RF preselection filter and an associated separate low-noise amplifier is often needed for each operating frequency band (or subband) to filter and attenuate harmful out-of-band blocking signals (or simply blockers), which can drive the receiver into compression. Blocking signals may also, e.g., desensitize the receiver and lower the signal-to-noise-ratio (SNR) of the desired received RF signal. However, in some systems such as in half-duplex RF transceivers where the receiver and transmitter do not operate simultaneously, it is possible to design the integrated radio receiver to be sufficiently linear so as to tolerate the out-of-band blocking signals without providing heavy filtering for them before they enter to the LNA. In such systems, it may be possible to omit the conventional band-dedicated RF preselection filters. This leads to lower complexity and bills of material (BOM) compared to the multiband receiver. However, some alternative filtering solution is usually still needed for rejecting certain blocking signals so as to ensure satisfactory performance for the receiver. BRIEF DESCRIPTION According to a first aspect, there is provided a tunable radio frequency filter for preselection in a multiband radio receiver or transceiver with a low-noise amplifier with a single-ended input. The tunable radio frequency filter comprises a first capacitor having a first terminal for connecting to at least one antenna of the multiband radio receiver or transceiver and a second terminal; and a series resonant circuit, connected between the second terminal of the first capacitor and the ground. The series resonant circuit comprises a first inductor and a tunable capacitor connected in series with first inductor and having a plurality of tuning values corresponding to operating frequency bands of the multi-band radio receiver or transceiver. The tunable capacitor is implemented in an integrated circuit. The series resonant circuit is configured to be resonant at a plurality of first subharmonics of frequencies of the operating frequency bands. A first subharmonic of a given frequency corresponds, here and in the following, to a frequency which is equal to said given frequency divided by two. According to a second aspect, there is provided a differential tunable radio frequency filter for a multiband radio receiver or transceiver with a low-noise amplifier with a differential input comprising an inverting input and a non-inverting input. The differential tunable radio frequency filter comprises a pair of tunable radio frequency filters according to the first aspect comprising a first tunable radio frequency filter for connecting to a non-inverting input of the differential low-noise amplifier and a second tunable radio frequency filter for connecting to an inverting input of the differential low-noise amplifier. According to a third aspect, there is provided a multiband radio receiver or transceiver with at least one low-noise amplifier with a single-ended input. Said multiband radio receiver or transceiver comprises at least one tunable radio frequency filter according to the first aspect acting as a preselection filter of the multiband radio receiver or transceiver. According to a fourth aspect, there is provided a multiband radio receiver or transceiver with at least one low-noise amplifier having a differential input. The multiband radio receiver comprises a differential tunable radio frequency filter according to the second aspect acting as a non-band-specific preselection filter of the multiband radio receiver or transceiver. The first, second, third and fourth aspects provide the technical effect that at least the first and second subharmonics of the operating frequencies of the multiple operating frequency bands of a multiband radio receiver or transceiver may be filtered using a single radio frequency filter. A second subharmonic of a given frequency corresponds, here and in the following, to a frequency which is equal to said given frequency divided by three. The first and second subharmonics are especially detrimental for the operation of the radio receiver or transceiv