Example RF Transceiver

FIG. 3 is a block diagram of an example radio frequency (RF) transceiver circuit 300, in accordance with certain aspects of the present disclosure. The RF transceiver circuit 300 includes at least one transmit (TX) path 302 (also known as a “transmit chain”) for transmitting signals via one or more antennas 306 and at least one receive (RX) path 304 (also known as a “receive chain”) for receiving signals via the antennas 306. When the TX path 302 and the RX path 304 share an antenna 306, the paths may be connected with the antenna via an interface 308, which may include any of various suitable RF devices, such as a switch, a duplexer, a diplexer, a multiplexer, and the like.

Receiving in-phase (I) and/or quadrature (Q) baseband analog signals from a digital-to-analog converter (DAC) 310, the TX path 302 may include a baseband filter (BBF) 312, a mixer 314, a driver amplifier (DA) 316, and a power amplifier (PA) 318. The BBF 312, the mixer 314, the DA 316, and the PA 318 may be included in a radio frequency integrated circuit (RFIC). For certain aspects, the PA 318 may be external to the RFIC.

The BBF 312 filters the baseband signals received from the DAC 310, and the mixer 314 mixes the filtered baseband signals with a transmit local oscillator (LO) signal to convert the baseband signal of interest to a different frequency (e.g., upconvert from baseband to a radio frequency). This frequency-conversion process produces the sum and difference frequencies between the LO frequency and the frequencies of the baseband signal of interest. The sum and difference frequencies are referred to as the “beat frequencies.” The beat frequencies are typically in the RF range, such that the signals output by the mixer 314 are typically RF signals, which may be amplified by the DA 316 and/or by the PA 318 before transmission by the antenna(s) 306. While one mixer 314 is illustrated, several mixers may be used to upconvert the filtered baseband signals to one or more intermediate frequencies and to thereafter upconvert the intermediate frequency (IF) signals to a frequency for transmission.

The RX path 304 may include a low noise amplifier (LNA) 324, a mixer 326, and a baseband filter (BBF) 328. The LNA 324, the mixer 326, and the BBF 328 may be included in one or more RFICs, which may or may not be the same RFIC that includes the TX path components. RF signals received via the antenna(s) 306 may be amplified by the LNA 324, and the mixer 326 mixes the amplified RF signals with a receive local oscillator (LO) signal to convert the RF signal of interest to a different baseband frequency (e.g., downconvert). The baseband signals output by the mixer 326 may be filtered by the BBF 328 before being converted by an analog-to-digital converter (ADC) 330 to digital I and/or Q signals for digital signal processing.

Certain transceivers may employ frequency synthesizers with a variable-frequency oscillator (e.g., a voltage-controlled oscillator (VCO) or a digitally controlled oscillator (DCO)) to generate a stable, tunable LO with a particular tuning range. Thus, the transmit LO may be produced by a TX frequency synthesizer 320, which may be buffered or amplified by amplifier 322 before being mixed with the baseband signals in the mixer 314. Similarly, the receive LO may be produced by an RX frequency synthesizer 332, which may be buffered or amplified by amplifier 334 before being mixed with the RF signals in the mixer 326. For certain aspects, a single frequency synthesizer may be used for both the TX path 302 and the RX path 304. In certain aspects, the TX frequency synthesizer 320 and/or RX frequency synthesizer 332 may include a frequency divider/multiplier that is driven by an oscillator (e.g., a VCO) in the frequency synthesizer. In some aspects, the transceiver circuit 300 may be implemented with a LIF offset to improve receiver NF, as described in more detail herein.

A controller 336 (e.g., controller/processor 280 in FIG. 2) may direct the operation of the RF transceiver circuit 300A, such as transmitting signals via the TX path 302 and/or receiving signals via the RX path 304. The controller 336 may be a processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof. A memory 338 (e.g., memory 282 in FIG. 2) may store data and/or program codes for operating the RF transceiver circuit 300. The controller 336 and/or the memory 338 may include control logic (e.g., complementary metal-oxide-semiconductor (CMOS) logic).

While FIGS. 1-3 provide wireless communications as an example application in which certain aspects of the present disclosure may be implemented to facilitate understanding, certain aspects described herein may be used for any of various other suitable systems.

Example Techniques for Dynamic Frequency Shifting to Improve Noise Figure

Some fifth-generation (5G) new radio (NR) and long-term evolution (LTE) downlink receivers may include a primary receive path and a secondary (diversity) receive path. The two paths may form a downlink pipe (DLP). In some implementations, a DLP may support reception from just one base station registered with one subscriber identity module (SIM) at a time. Some applications support reception on two SIMs from two carriers using the same DLP. Thus, a local oscillator arrangement may support both diversity reception for a single SIM and single path reception (e.g., non-diversity) with two SIMs where a primary receive path (PRx) would connect to a base station or carrier of the first SIM and the diversity receive path (DRx) would connect to a base station or carrier of a second SIM. Some multi-SIM (MSIM) operations involve using multiple DLPs for different SIMs, and some MSIM operations use only one DLP with a PRx and a DRx for different SIMs.

FIG. 4 illustrates a DLP 400 including a PRx 402 and DRx 404. The PRx 402 may include at least one antenna 406 coupled to a radio frequency (RF) front-end (FE) 408. The RF FE 408 may include a low-noise amplifier (LNA) (e.g., corresponding to LNA 324 of FIG. 3) for amplifying a signal received from the antenna. The amplified signal may be provided to a mixer 410 (e.g., corresponding to mixer 326 of FIG. 3) for down-conversion (e.g., signal down-conversion from RF to a baseband (BB) frequency) using a LO signal (not shown). The mixer 410 generates a BB signal that is provided to a BB filter (BBF) 412 (e.g., corresponding to the BBF 328 of FIG. 3) to generate a filtered signal that is then converted from an analog domain to the digital domain via an analog-to-digital converter (ADC) (e.g., corresponding to ADC 330 of FIG. 3) and demodulated using demodulation circuitry 414.

Similarly, the DRx 404 may include at least one antenna 426 coupled to an RF FE 428. The RF FE 428 may include an LNA for amplifying a signal received from the antenna. The amplified signal may be provided to a mixer 430 for down-conversion (e.g., from RF to a baseband (BB) frequency) using another LO signal. The mixer 430 generates a BB signal that is provided to a BBF 432 to generate a filtered signal that is then converted from the analog domain to the digital domain via an ADC and demodulated using demodulation circuitry 434.

In some aspects, multiple synthesizers 491, 493 may be used to generate local oscillator signals, such as a low-power mode (LPM) synthesizer 493 (e.g., implemented using a ring oscillator) and a high-performance mode (HPM) synthesizer 491 (e.g., implemented using an inductor-capacitor (LC) oscillator). The LO signal from synthesizer 491 may be provided to multiplexers 496, 498 (e.g., through a frequency divider 494, labeled “Div N”), and the LO signal from synthesizer 493 may be provided to multiplexers 496, 498 through a buffer 499. The multiplexers 496, 498 may be controlled to direct each LO signal to either the PRx or DRx (e.g., to either mixer 410 for the PRx 402 or mixer 430 for the DRx 404 for down-conversion). For some MSIM applications, the PRx may be associated with a first subscriber (sub1), and the DRx may be associated with a second subscriber (sub2) or vice versa.

In some cases, one receive path (e.g., PRx 402) may be used for traffic, and the other receive path (e.g., DRx 404) may be used for page reception or vice versa. In some cases the receive path used for traffic may use a high-performance synthesizer (e.g., synthesizer 491) with good phase noise. The receive path used for page reception may use the low-performance synthesizer (e.g., synthesizer 493) with poor phase noise to save the transceiver's power, area, and cost. In some other cases, when the signal-to-noise ratio (SNR) specification for traffic is low, traffic may use the low-performance synthesizer (e.g., synthesizer 493). In such cases, page reception may be performed through a high-performance synthesizer (e.g., synthesizer 491).

It may be difficult to achieve proper isolation between the PRx LO and DRx LO (e.g., an isolation of 55 dB), especially in small footprint implementations (e.g., small silicon area for an RF chip) and/or when supply and ground nodes (or circuits) are shared between the paths. Thus, when the LO frequencies for sub1 and sub2 are close (e.g., within a frequency difference threshold), degradation in the noise figure (NF) for sub1 and sub2 may occur.

Sub1 and sub2 may be operated using different bands, such as a low-band (LB), mid-band (MB), high-band (HB), ultra-high band North America (UNA), or new radio unlicensed (NRU) band. If sub1 and sub2 are operating using the same band (e.g., HB), NF degradation may occur. For example, if sub1 and sub2 operate within HB and the LO frequencies of sub1 and sub2 are within a frequency difference threshold (e.g., 5 MHz), NF degradation (e.g., 1 dB NF degradation) may occur at the antenna ports for sub1 and sub2. If the LO frequencies for sub1 and sub2 are the same, a higher NF degradation (e.g., 16.8 dB NF degradation) may occur at the antenna ports, and even higher NF degradation (e.g., 36 dB NF degradation) may occur at the receiver input of the radio (e.g., chip including the mixers 430, 410).

FIGS. 5A, 5B, and 5C illustrate example LO frequencies for sub1 and sub2. As shown in FIG. 5A, the sub1 LO (LO1) frequency may be equal to the sub2 LO (LO2) frequency, in which case high NF degradation may occur as described. Even though both sub1 and sub2 are assigned the same absolute radio-frequency channel number (ARFCN) and although Sub1 can receive a page for Sub2, through resource sharing in the frequency domain (e.g., through the concept of page sharing) the UE may decide to operate with two different LO signals operating at the same frequency, causing the NF degradation described herein. Page sharing refers to an implementation where a page of one subscriber is received by another subscriber, through resource sharing in frequency domain, using the same ARFCN. Page sharing may be implemented when both subscribers are using the same radio technology and the same operator (or network sharing operators).

In some aspects, a frequency difference threshold 502 may be identified. For example, if both sub1 and sub2 are operating in HB, a frequency difference threshold 502 of 5 MHz may be identified so that the NF degradation does not exceed 1 dB. As shown in FIG. 5B, if the difference between the LO1 and LO2 frequencies is less than the frequency difference threshold 502, high NF degradation may occur (e.g., greater than 1 dB). In some cases, as shown in FIG. 5C, the LO1 and LO2 frequencies may be within the frequency difference threshold 502, and the LO frequencies may cause a spur (e.g., beat frequency component) within the baseband channel bandwidth, causing issues with signal processing during reception. For example, this spur within the baseband channel bandwidth may occur if the following expression is true:

❘
"[LeftBracketingBar]"

m
×
LO
⁢
1
⁢

Frequency
×
LO
⁢
2
⁢

Frequency

❘
"[RightBracketingBar]"

<

Signal
⁢

Bandwidth

2

where m and n are positive integers and Signal Bandwidth is the RF System BW of Traffic/Paging Sub. Certain aspects of the present disclosure are directed towards dynamically determining and implementing a low intermediate frequency (LIF) offset for a subscriber to provide separation, that is greater than the frequency difference threshold, between the frequencies of the subscribers.

FIG. 6A illustrates example techniques for implementing a LIF offset (labeled “LIF_OFF”), in accordance with certain aspects of the present disclosure. As shown, traffic may be received by the PRx (e.g., the PRx 402) at the input of LNA 602 to generate an amplified signal that is downconverted by mixer 410. The input signal of the LNA 602 may have a bandwidth with a center frequency equal to the LO1 frequency. The downconverted signal may be filtered by a BBF 412 to generate a filtered signal. As shown, the center frequency of the filtered signal bandwidth may be at direct current (DC) (e.g., 0 hertz). The filtered signal is then converted from the analog domain to the digital domain via an ADC 606, as shown.

FIG. 6B illustrates a transceiver with an LNA inside or outside the transceiver. For example, the LNA 602 could be inside the RF transceiver as shown, or the LNA may be outside the transceiver. In some cases, amplification may be implemented with a cascade of two LNA's including an LNA 651 outside the transceiver followed by the LNA 602 inside the transceiver, as shown in FIG. 6B. The transceiver may be coupled to an antenna through an antenna interface, as shown.

Referring back to FIG. 6A, a page may be received by the DRx (e.g., the DRx 404) at the input of LNA 604 to generate an amplified signal that is downconverted by mixer 430. The input signal of the LNA 604 may have a bandwidth with a center frequency equal to the LO2 frequency. The downconverted signal may be filtered by a BBF 432 to generate a filtered signal. As shown, the center frequency of the filtered signal bandwidth (labeled “BW”) may be at DC. The filtered signal is then converted from the analog domain to the digital domain via an ADC 608, as shown.

In some aspects, a LIF offset (LIF_OFF) may be implemented. To implement the LIF offset, the LO2 frequency may be shifted by the LIF offset. Thus, the new frequency of the LO signal provided to mixer 430 may be equal to the LO2 frequency plus LIF_OFF, as shown. As a result, the filtered signal at the output of the BBF may have a new center frequency (f_{center_new}) that is equal to a no-offset center frequency (e.g., center frequency without applying the LIF offset, which is DC) plus the LIF offset, as shown. Thus, the new bandwidth post applying the LIF offset may be equal to:

B
⁢
W

+

2
×
LIF_OFF

The filtered signal is then converted from the analog domain to the digital domain via an ADC 608, as shown.

In some aspects, a wireless device may determine whether to apply a LIF offset during the tuning of a subscriber by checking the active tune configuration (e.g., if present) of the other subscriber. For every subscriber tuning, the device may determine whether to apply a dynamic LIF offset by comparing the tune configuration for that subscriber with a previously configured tune configuration of the other subscriber. For instance, a controller (e.g., using an RF software driver) may check the separation between the LO frequency (e.g., tune configuration) of the first subscriber and the LO frequency of the second subscriber.

Suppose the separation is more than a frequency difference threshold (e.g., frequency difference threshold 502 described with respect to FIGS. 5B and 5C). In that case, no LIF offset may be implemented. A LIF offset may be implemented if the separation is less than the frequency difference threshold. The LIF offset to be applied may be determined per band group based on RF integrated circuit (RFIC) characterization. In other words, for each band group (e.g., LB, MB, HB), the frequency difference threshold may be determined so that the NF degradation does not exceed 1 dB. An RF driver may be used to run a sequence to determine if a spur (m×LO1 frequency−n×LO2 frequency) will fall in the channel bandwidth in the baseband for either traffic or paging (e.g., in the baseband of sub1 or sub2). LIF offset may be applied if the spur will fall in the channel bandwidth. LIF offset application is then performed during the tuning of that subscriber (e.g., one of the subscribers) with digital configuration for de-rotation. For example, for de-rotation, the spectrum may be shifted back in the digital domain to compensate, or at least adjust, for the LIF offset applied in the analog domain.

FIG. 7 illustrates example operations 700 for the application of a LIF offset, in accordance with certain aspects of the present disclosure. At block 702, a controller for a first subscriber (SUB1) may send, to a technology controller 706 (e.g., controller of the radio access technology, such as long-term evolution (LTE) or new radio (NR)), a request for LO tuning for the first subscriber. For example, the controller may send tuning requested information that may include a requested local oscillator frequency for the first subscriber. The tuning request information for the first subscriber may be sent to the radio 708 and the requested tuning of the LO may be performed by an LO tuner 710. At block 704, a controller for a second subscriber (SUB2) may send to the technology controller 706 a request for LO tuning for the second subscriber. The controller 706 may send, to the radio 708, the tuning request information for the second subscriber. The radio 708 may aggregate (e.g., compare) the tuning information for the first subscriber and the second subscriber to determine whether a LIF offset is to be applied for the second subscriber (e.g., since the second subscriber's tuning request occurred later in time). The radio 708 may then compute the LIF offset to be applied. The tuner 710 may then tune the LO frequency for the second subscriber in the analog domain and configure the de-rotation in the digital domain for the second subscriber.

While some example provided herein are described with respect to LTE and NR, any suitable radio access technology (RAT) or combination of RATs for SUB1 and SUB2 may be used. For example, SUB1 and SUB2 may be any of NR, LTE, wideband code division multiple access (WCDMA), global system for mobile (GSM), or CDMA 2000 (C2k), and in any combination between SUB1 and SUB2. Thus, controller 706 may process requests from SUB1 and SUB2 across two different RATs.

FIG. 8 illustrates pseudo code 800 for determining a LIF offset, in accordance with certain aspects of the present disclosure. As shown, if the PRx LO (LO signal for the PRx, labeled “PRX_LO”) and DRx LO (LO signal for the DRx, labeled “DRX_LO”) are both within LB, no LIF may be applied (e.g., since previous testing may show that NF degradation is acceptable for LB operations even if the LO frequencies of the subscribers are the same). Different LIF offsets may be applied depending on operations in different bands. For example, if the PRX_LO and DRX_LO are within MB, then a LIF value (labeled “LIF” in code 800) may be set to a frequency F1. The code 800 may check if the difference between the LO frequencies (represented by expression abs (PRX_LO-DRX_LO)) is less than the LIF value. Then, one of PRX_LO and DRX_LO (e.g., “PRX_LO/DRX_LO” in code 800) for which LIF offset is to be applied may be set per equation:

PRX_LO
/
DRX_LO

=

PRX_LO
/
DRX_LO

+
/
-

(

abs
⁡
(

PRX_LO
-
DRX_LO

)

-
LIF

)

The new effective bandwidth (labeled “Effective_BW”) with the LIF offset may be determined per equation: