A receiver for LTE Rel-11 and beyond supporting non-contiguous carrier aggregation

Abstract

Carrier aggregation (CA) is introduced in 3GPP LTE to meet the demand for further increased bitrates. While LTE Rel-10 supports simultaneous reception of two carriers either in contiguous intra-band or in inter-band CA configuration, the upcoming LTE Rel-11 will add support for non-contiguous (NC) carriers within bands. Supporting NC CA in handsets is a demanding challenge for several reasons. Foremost, the total bandwidth spanned by the carriers may be several times the bandwidth of the individual carriers, possibly spanning an entire band with interfering signals between desired carriers. Furthermore, the distance between TX and RX carriers will vary and worse, may be much smaller than the fixed duplex distance for LTE Rel-8 and W-CDMA single carrier operation [2][3][4][5].This paper presents a single-chip receiver supporting both NC intra-band and inter-band CA with the capability to receive up to three carriers simultaneously. The receiver block diagram is illustrated in Fig. 19.5.1. Using two configurable RF frontends the receiver spans frequencies from 700 to 1500MHz in low-band and 1800 to 2700MHz in high-band. The baseband section contains three IQ baseband paths. Each contains a pair of channel-select filters and ADCs capable of handling one LTE carrier with a bandwidth of 5, 10, 15, or 20MHz. The RF front-ends are connected to a switch unit that allows the signal from each frontend to be routed directly to one of the baseband paths to operate as a regular homodyne receiver for single-carrier reception. Inter-band CA reception with two carriers is supported by configuring the receiver as two parallel homodyne paths operated at different RF frequencies. Intra-band CA reception is achieved by double conversion where one of the RF front-ends first downconverts both the carriers to an intermediate frequency (IF) equal to half the carrier separation. The RF mixer output signal is then routed to the IF circuit where the two carrier components are separated and downconverted to baseband. Since the two intraband carriers only occupy one RF front-end and two baseband paths, a third carrier can be downconverted using the other RF front-end and the remaining baseband path as a homodyne receiver.

A 0.02 mm<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex></formula> 59.2 dB SFDR 4th-Order SC LPF With 0.5-to-10 MHz Bandwidth Scalability Exploiting a Recycling SC-Buffer Biquad

“…For instance, two real poles can be built with one buffer [ Fig. 1(b)] under a 3-phase 33% clock, yielding a multiplicative transfer function of two independent real poles as given by (2) where and . Obviously, one buffer is saved (so as the static power), but the buffer has to be 1.5x faster for the same settling accuracy as that of Fig.…”

“…Both and can serve as the outputs. Assuming all capacitors are fully charged during each clock phase, the z-domain transfer function of and can be expressed as (3) where and are the same as (2). The transfer function in the s-domain (assuming is given by (4) From (4), Q , and can be handily chosen.…”

“…I N RESPONSE TO the ever-increasing demand for higher data rates, long-term evolution (LTE) and wireless local-area network (WLAN) radios have introduced the carrier aggregation (CA) and multiple-input multiple-output (MIMO) techniques to enhance their throughput [1], [2]. Yet, each CA or MIMO channel calls for a separate radio front-end, pressuring the area budget of each analog function.…”

“…Yet, each CA or MIMO channel calls for a separate radio front-end, pressuring the area budget of each analog function. In fact, merely the numerous channel-selection low-pass filters (LPFs) occupy a substantial area of the radio, e.g., % in [2]. For common LPF topologies like active-RC and -C that hinge on passives to define the time constant, the die area can be relatively large because of bandwidth (BW) tuning and kT/C requirement.…”

A multi-band Rel9 WCDMA/HSDPA/TDD LTE and FDD LTE transceiver with envelope tracking

“…The high bandwidth of LTE and the use of carrier aggregation (CA) enable higher data rates but pose new challenges on the RFIC design [1]- [5]. The demand for multiple bands complicates transceiver design, at the same time backward compatibility and the need for lower power consumption on the mobile phones require new techniques to save current adaptively.…”