Concurrent multi-band low noise amplifier architecture

Details Concurrent multi-band low noise amplifier architecture Concurrent multi-band low noise amplifier architecture

2001-03-28

2004-01-06

Lee, Benny (Department: 2817)

Wave transmission lines and networks

Coupling networks

With impedance matching

C330S126000, C330S302000

Reexamination Certificate

active

06674337

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of radio frequency (“RF”) transceivers and more particularly to monolithic low noise amplifier architectures used in wireless receivers that can operate at multiple frequency bands simultaneously.
BACKGROUND OF THE INVENTION
Wireless communications systems have exhibited remarkable growth over the past decade. Wireless voice and data applications are being enabled by rapidly emerging wireless technologies, such as cellular telephony, personal communications systems and wireless local area networks (WLAN's), to name a few. Digital modulation techniques, miniaturization of transceivers due to advances in monolithic integrated circuit designs and the development of high frequency, microwave and millimeter wave RF systems in both the licensed and unlicensed bands, have all contributed to improving the quality and bandwidth capacity of these system and to reducing the size and costs of the components.
These systems are having a profound effect on societies. For example, they are enabling many work forces in our global, service and information based economy to become “untethered” from their information sources and conventional wired communications mechanisms. Moreover, wireless communication systems are enabling developing countries to provide instant telephone service to new subscribers who otherwise would have to wait years for wireline access.
While many wireless applications work fairly well and have found widespread acceptance (e.g. mobile/cellular telephones), they continue to suffer from numerous drawbacks. One recognized problem in the cellular phone industry is the lack of universal standards for both signal transmission modes (analog or digital) and within digital mode the frequency bands and signal processing protocols (e.g., TDMA, CDMA, WDM, GSM, etc.). This unfortunately requires users who wish to use cell phones in different geographic areas that employ different telecommunications standards to either carry multiple telephones or to use phones designed to operate in multiple frequency modes and bands.
It would thus be highly desirable to have a receiver that can operate at multiple and discrete frequency bands. This would offer several benefits. A multi-band receiver could enable the design of a single device that can operate under multiple standards, such as GSM (with a center frequency of 900 MHz) and DECT (center frequency of 1800 MHz), thereby eliminating the need for one device per standard. While dual band receivers have been introduced that indeed increase the functionality of such communication systems, such receivers switch between two different bands and can receive only one band at a time.
FIG. 1
is a schematic of such a conventional dual band architecture. As seen, an incoming signal, V
in
, is received at a switch
10
(for simplicity the antenna and filter are not shown). If the signal is in a first predetermined frequency band, &ohgr;
1
, the switch moves to the top signal processing path tuned to match and amplify signals only in this band. The signal is then impedance matched and amplified at low noise amplifier (“LNA”)
20
, mixed with local oscillator, LO1, at mixer
22
, filtered at band pass filter
24
and mixed again with local oscillator, LO2,
26
, until is exits as V
out
for further processing (e.g. digital signal processing). Similarly, if the incoming signal is in the second predetermined frequency band, &ohgr;
2
, the switch moves to the bottom signal processing path tuned to match and amplify signals only in this band, through LNA
30
, mixer
32
, BPF
34
and mixer
36
and again exists as Vout. The frequency of LO1 is (&ohgr;
1
+&ohgr;
2
)/2 and the frequency of LO2 is (&ohgr;
1
−&ohgr;
2
)/2. While this functionality adds to a device's versatility, such as in the case of a dual-band digital cellular phone, these receivers are more costly than single band receivers and they are not sufficient for the next-generation of multi-functional devices, such as a cell phone with a GPS receiver and a bluetooth interface.
Another problem with conventional wireless technology relates to bandwidth limitations. The diverse range of modem wireless applications demand wireless communications systems and transceivers with greater bandwidth capacity and flexibility than can be currently supplied. Increased bandwidth capacity is necessary for many wireless applications to become a reality. Wireless broadband Internet applications (e.g. browsing, e-commerce, streaming audio and video), wireless video messaging, wireless video games, and remote video monitoring are just a few examples of applications that will be delivered over the next generations of wireless networks. Conventional solid-state RF, or wireless, receiver architectures, such as superheterodyne and direct conversion receivers, accomplish high selectivity and sensitivity by designing them for narrow-band operation at a single RF frequency. Unfortunately, these modes of operation are of limited functionality because they limit the system's available bandwidth and robustness to channel variations. On the other hand, wide-band modes of operation are more sensitive to out-of-band signals due to transistor non-linearity, which can introduce severe bottlenecks in system performance.
It would thus be highly desirable to have such a low cost, concurrent multi-band receiver. As used herein a concurrent multi-band receiver is one that can process signals at multiple and discrete frequency bands simultaneously. This would enable a single path receiver to significantly increase its bandwidth capacity (bit rate). A concurrent multi-band receiver design could also be used for supplying redundancy in mission critical data transmission application. The reliability of the received signal would be greatly increased with simultaneous transmission of the same signal in multiple bands for diversity of signal.
Using conventional receiver technology, the only way to theoretically provide concurrent multi-band functionality is to design into a receiver multiple independent signal paths with multiple sets of components (antennas, LNA's, downconverter etc.). Such a dual-band receiver is shown schematically in FIG.
2
. As shown, this design is similar to the dual band receiver in
FIG. 1
without the switch
12
and separate outputs, V
out1
and V
out2
. This scheme essentially equivalent to designing multiple single band receivers, each tuned to a different band and stuffed into one package. Unfortunately, this architecture significantly increases the cost, footprint and power dissipation of a receiver, and tends to make such solutions impractical, at least for commercial applications. Thus, a challenge for modern receiver design is to create concurrent multi-band functionality using as little real estate (and ideally monolithically) and as little power dissipation as possible (and perhaps no more than single band receivers), while keeping the incremental production costs above the conventional single band receiver to a minimum.
The LNA is a critical front end component of a wireless receiver. Its function is to take the relatively weak signal received at the antenna and, after filtering, amplify it with maximum power transfer and with a minimum added noise for further processing (downconversion, etc.). The maximum power transfer is achieved by designing the LNA to have an input impedance that matches a characteristic input impedance of the antenna, which is commonly 50 ohms. Thus, a true concurrent multi-band LNA, as a critical front end component of a concurrent multi-band receiver, must be capable of (1) matching the characteristic input impedance of the received signal at the antenna at the multiple frequency bands, simultaneously; (2) simultaneously amplifing the received signal(s) at each of the bands; and (3) accomplishing the above with minimum electrical noise added.
As in the case of conventional dual band receivers described above, in conventional dual-band LNA's, for example, either one of two single-band LNA&

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