Telecommunications – Transmitter – Frequency conversion
Reexamination Certificate
2001-07-31
2004-05-18
Trinh, Sonny (Department: 2685)
Telecommunications
Transmitter
Frequency conversion
C455S180100, C455S141000, C455S313000
Reexamination Certificate
active
06738604
ABSTRACT:
BACKGROUND
I. Field of the Invention
The present invention relates to electronic communications. More particularly, the present invention relates to Intermediate Frequency (IF) filtering.
II. Description of the Related Art
Electronic communication devices often modulate the desired signal onto a RF carrier frequency to provide frequency diversity over a plurality of channels. The distinct frequencies may then be simultaneously transmitted across a single link with a minimum of interaction between the plurality of channels. The link may be a single wire, multiple wires, coaxial transmission line, wireless link, optical fiber, or any other known communication link.
In a transmitter, baseband signals are upconverted onto a desired transmit frequency. While in a receiver, the received signal is downconverted to a baseband signal. The upconversion in a transmitter, and complementary downconversion in a receiver, is often performed in a plurality of stages rather than a single conversion.
Many communication devices utilize a dual conversion architecture design for the receiver and transmitter.
FIG. 1
shows a block diagram of a wireless transceiver such as may be used in a wireless phone. Although a transceiver is shown in
FIG. 1
, it can be seen that the component parts may be isolated to perform only the transmitter or receiver functions. Similarly, although a wireless transceiver is shown in
FIG. 1
, a wire line device may be configured by eliminating the antenna or coupling the antenna to a wire line connection.
An antenna
10
may be used to interface the wireless device
100
to incoming radio waves. The antenna
10
may also be used to broadcast the signal from the transmitter. Incoming radio waves coupled to the wireless device
100
at the antenna
10
are next coupled to a duplexer
20
. The duplexer
20
filters the incoming receive band signal but may also be used to electrically isolate the transmit power from the receive path while allowing the transmitter and receiver to use the same antenna. The duplexer
20
couples the signals in the receive path to a Low Noise Amplifier (LNA)
22
while simultaneously rejecting signals outside of the receive band. Ideally, the duplexer
20
rejects all signals in the transmit band such that they do not interfere with the receive band signals. However, practical implementations of duplexers
20
provide only limited rejection of signals in the transmit band.
The LNA
22
following the duplexer
20
is used to amplify the receive signal. The LNA
22
may also be the major contributor to the receiver's noise figure. The noise figure of the LNA
22
adds directly to the noise figure of the receiver while the noise figure of subsequent stages is reduced in proportion to the LNA
22
gain. Thus, the LNA
22
is typically chosen to provide a minimal noise figure in the receive band while amplifying the receive signal with sufficient gain to minimize noise figure contributions from subsequent stages. There are competing design requirements, such as DC power requirements and device third order intercept point, that make the choice of LNA
22
gain a trade off of many design constraints. The signal amplified in the LNA
22
is coupled to an RF filter
24
. The RF filter
24
is used to provide further rejection to signals outside of the receive band. The duplexer
20
may not be capable of supplying sufficient rejection of signals outside of the receive band so the RF filter
24
supplements the prior filtering. The RF filter
24
is used after, rather than before, the first LNA
22
stage in order to reduce the filter's contribution to the receiver noise figure. The output of the RF filter
24
is coupled to a second LNA
26
. The second LNA
26
is used to further amplify the received RF signal. A second LNA
26
stage is typically used where sufficient gain cannot be achieved in a single LNA stage while also satisfying third order intercept constraints. The output signal from the second LNA
26
is coupled to an input of a RF mixer
30
.
The RF mixer
30
mixes the amplified receive signal with a locally generated frequency signal to downconvert the signal to an Intermediate Frequency (IF). The IF output of the RF mixer
30
is coupled to an IF amplifier
32
that is typically used to increase the signal level. The IF amplifier
32
typically has limited frequency response and does not amplify the upconverted signal that is output from the RF mixer
30
. The output of the IF amplifier
32
is coupled to an IF filter
34
.
The IF filter
34
is used to filter the IF from a single receive channel. The IF filter
34
typically has a much narrower frequency response than does the RF filter
24
. The IF filter
32
can have a much narrower bandwidth since the RF mixer
30
typically downconverts the desired RF channel to the same IF regardless of the frequency of the RF channel. In contrast, the RF filter
24
must pass the entire receive band since any channel in the receive band can be allocated to the communication link. The output of the IF filter
34
is coupled to a receive Automatic Gain Control (AGC) amplifier
36
. The AGC amplifier
36
is used to maintain a constant amplitude in the receive signal for the subsequent stages. The gain of the AGC amplifier
36
is varied using a control loop (not shown) that detects the amplitude of the amplifier's output. The output from the AGC amplifier
36
is coupled to an IF mixer
40
.
The IF mixer
40
downconverts the IF signal to a baseband signal. The Local Oscillator (LO) used in conjunction with the IF mixer
40
may be separate and distinct from the first LO
150
. The baseband output of the IF mixer
40
is coupled to a baseband processor
102
. The baseband processor
102
block represents subsequent processing that is performed on the baseband signal. Examples of subsequent processing include, but are not limited to, despreading, deinterleaving, error correction, filtering, and amplification. The received information is then routed to the appropriate destination. The information may be used within the wireless device or may be routed to a user interface such as a display, loudspeaker, or data port.
The same baseband processor
102
may also be used in the complementary transmitter. Information to be transmitted is input to the baseband processor
102
where it may be, for example, interleaved, spread, and encoded. The processed signal is coupled to a transmit IF mixer
110
where the baseband signal is upconverted to a transmit IF. The transmit LO
112
used in conjunction with the transmit IF mixer
110
is generated separately from the first LO
150
and the receive IF LO
42
.
The upconverted transmit IF signal output from the IF mixer
110
is coupled to a transmit AGC amplifier
114
. The transmit AGC amplifier
114
is used to control the amplitude of the transmit IF signal. Amplitude control of the IF signal may be required to ensure the signal is maintained within the linear regions of all subsequent amplifier stages. The output of the AGC amplifier
114
is coupled to a transmit IF filter
116
that is used to reject unwanted mixer and amplifier products. The filtered output is coupled to a transmit RF mixer
120
. The transmit RF mixer
120
is used to upconvert the transmit IF to the proper transmit RF frequency.
The upconverted RF output from the transmit RF mixer
120
is coupled to a first transmit RF filter
122
. The first transmit RF filter
122
is used to reject undesired mixer products. The output of the first transmit RF filter
122
is coupled to a driver amplifier
124
. The driver amplifier
124
amplifies the signal to a level desired by the subsequent power amplifier
128
. Before the signal is applied to the power amplifier
128
the signal is filtered in a second transmit RF filter
126
. The second transmit RF filter
126
is used to further reject mixer products and is also used to reject out of band products that are generated by the driver amplifier
124
. The out of band products generated by the driver amplifier
126
may be harmoni
Brown Charles D.
Qualcomm Inc.
Seo Howard H.
Trinh Sonny
Wadsworth Philip
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