Amplifiers – With semiconductor amplifying device – Including plural amplifier channels
Reexamination Certificate
2002-09-13
2004-09-28
Nguyen, Khanh Van (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural amplifier channels
C330S12400D
Reexamination Certificate
active
06798294
ABSTRACT:
SCOPE OF THE INVENTION
The invention relates to low noise amplifiers (LNAs). It is particularly related to an LNA having multiple inputs in several frequency bands.
BACKGROUND OF THE INVENTION
A radio signal sent from a transmitter through a radio channel and received by a receiver suffers from propagation loss. Even though the transmission power from a transmitter such as a base station may be high, the received signal at a receiver such as a mobile station may be very low. According to the GSM standard, a mobile station needs to be able to receive signals of a level of −102 dBm without excessive Bit Error Rate (BER).
The propagation loss is not the only factor having an impact on radio reception. The transmitted signal is further reflected from various surfaces on its way causing multipath propagation. The signals arriving at the receiver via different paths may have opposite or interfering phases and thus may cancel each other out or interfere with each other. Noise from several sources, for example other mobile stations or systems, broadcast systems, radar and non-electromagnetic compatibility (EMC) compliant devices may also be added to the signal.
Low Noise Amplifiers (LNAs) are typically used as a first amplifying stage in radio receivers to amplify a received low-level radio signal to a higher level by adding as little noise as possible to the signal. In communications systems that just use one frequency band one LNA can be optimised for that particular frequency band.
To optimise an LNA for a certain frequency band, inductors are commonly used. Traditionally inductors have been bulky components, whereas a general aim in all electronics design is miniaturisation. Also radio receivers are commonly wanted to be implemented by integrated circuits, where inductance can be realized by planar inductors. Planar inductors, however, still need to use a large area of a semiconductor die compared to transistors.
The diversity of different mobile communications standards around the world has raised a need for mobile stations capable of communicating in several frequency bands. A mobile station can be constructed to work in several communications systems using different frequency bands, such as the 900 MHz GSM (Global System for Mobile Communications) system in Europe and the 1900 MHz TDMA (Time Division Multiple Access) system in US. Several frequency bands can also exist within one single system. For example, GSM systems now work in 900 MHz and 1800 MHz frequency bands in Europe and in 1900 MHz frequency band in the USA. The GSM system will be implemented in the USA also in the 800 MHz frequency band and will, thus, be using two separate frequency bands also in the USA. The third generation cellular communications system known as Universal Mobile Telephone System (UMTS) being specified by Third Generation Partnership Project (3GPP) also uses several frequency bands. A single mobile station working according to two systems, out of which at least one uses several frequency bands, has to use at least three frequency bands.
In order to provide this functionality, it has been proposed to use a dual band receiver such as the dual band receiver
100
shown in FIG.
1
. The dual band receiver
100
comprises two receiver branches
103
,
104
sharing an antenna
101
for receiving an RF signal and a band switch
102
. The receiver branches
103
,
104
further comprise band-pass filters
111
,
121
, LNAs
112
,
122
as well as in-phase mixers (I-mixers)
131
,
141
and quadrature-phase mixers (Q-mixers)
135
,
145
for mixing the RF signal with the respective local oscillator signals. Further, the receiver branches
103
,
104
comprise I-filters
133
,
143
and Q-filters
137
,
147
, I-Local Oscillator (I-LO) inputs
132
,
142
, Q-Local Oscillator (Q-LO) inputs
136
,
146
as well as I-outputs
134
,
144
and Q-outputs
138
,
148
. The LNAs
112
,
122
may be, for example, variable gain LNAs, as described in the U.S. Pat. Nos. 5,999,056 (Fong) or 6,046,640 (Brunner).
An RF signal sent by a Base Transceiver Station (BTS, not shown) is received by the antenna
101
. According to which frequency band the RF signal occupies, it is connected by the band switch
102
to either one of the receiver branches
103
,
104
. The band switch
102
is controlled by a control signal from a controlling unit (not shown). If a first frequency band is used, the RF signal is connected to the receiver branch
103
, where the RF signal is first filtered by the band-pass filter
111
. After filtering, the RF signal is amplified by the LNA
112
, which has been optimised for the first frequency band. The amplified RF signal is split and routed to the I-mixer
131
and to the Q-mixer
135
. An I-LO signal is injected to the I-LO input
132
and a Q-LO signal is injected to the Q-LO input
136
. The I-LO signal and the Q-LO signal are at the same frequency, but with a 90-degree phase difference. The I-mixer
131
and the Q-mixer
135
form downconverted signals by mixing the RF-signal and the injected LO-signals. From the I-mixer
131
the downconverted signal is fed to the I-filter
133
and the resultant I-signal is output through the I-output
134
. From the Q-mixer
135
the downconverted signal is fed to the Q-filter
137
and the resultant Q-signal is output through Q-output
138
.
If the RF signal occupies a second frequency band for which the receiver branch
104
is suitable, the receiver branch
104
will be chosen by the band switch
102
. The operation of the receiver branch
104
corresponds to that of the receiver branch
103
as described above.
The solution of the dual band receiver
100
is complicated because it demands two full receiver branches, one for each frequency band which is used. Therefore, alternative dual band receiver arrangements have been proposed.
An alternative dual band receiver
200
known in the prior art and shown in
FIG. 2
comprises an antenna
201
, a first band switch
202
, a band-pass filter
203
,
204
for each one of the used frequency bands, a second band switch
206
, an LNA
205
and a micro controller
208
. The dual band receiver
200
further comprises an I-mixer
211
, an I-LO input
212
, an I-filter
213
, and an I-output
214
, as well as a Q-mixer
215
, a Q-LO input
216
, a Q-filter
217
, and a Q-output
218
.
An RF signal sent by a BTS (not shown) is received by the antenna
201
. According to which frequency band the RF signal occupies it is connected by the first band switch
202
to either one of the band-pass filters
203
,
204
. The first band switch
202
and the second band switch
206
are controlled synchronously by a control signal from the micro controller
208
. If the RF-signal occupies a first frequency band, the RF signal is connected to the band-pass filter
203
. After the RF signal has been filtered, the second band switch
206
connects the used band-pass pass filter
203
to the LNA
205
so that the RF signal can be amplified. The amplified RF signal is split and routed to the I-mixer
211
and to the Q-mixer
215
. An I-LO signal is injected to the I-LO input
212
and a Q-LO signal is injected to the Q-LO input
216
. The I-LO signal and the Q-LO signal are at the same frequency, but with a 90-degree phase difference. The I-mixer
211
and the Q-mixer
215
form downconverted signals each by mixing the RF signal and the injected LO-signals. From the I-mixer
211
the downconverted signal is fed to the I-filter
213
and the resultant I-signal is output through the I-output
214
. From the Q-mixer
215
the downconverted signal is fed to the Q-filter
217
and the resultant Q-signal is output through Q-output
218
.
If the RF-signal occupies a second frequency band, the RF signal is connected to the band-pass filter
204
. After the RF signal has been filtered, the second band switch
206
connects the used band-pass filter
204
to the LNA
205
so that the RF signal can be amplified. The amplified RF signal is handled in a way corresponding to that described in the preceding paragraph.
The dual band receive
Harrington & Smith ,LLP
Nguyen Khanh Van
Nokia Corporation
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