22-05-2012, 03:50 PM
NF Direct Conversion Receiver for 3G WCDMA
[attachment=22745]
Introduction
The wide-band code division multiple access
(WCDMA) standard has been developed by the
Third Generation Partnership Project as a standard
for next generation digital mobile phone
applications [1]. The WCDMA standard achieves
higher data rates, channel capacity, and more
efficiency than current 2G systems.
Direct Conversion Receiver Architecture
In direct conversion topology, there is no
significant filtering of RF signals outside the
receiving band before the mixer and baseband
circuitry except in the duplexer, and the most
serious signal may come from Tx leakage. These
lead to high linearity requirements, which burden
the system. In the implemented receiver this work,
as shown in Fig. 1, an external interstage filter is
inserted after the LNA1 to provide additional Tx
and out-of-band attenuation and thus relaxes the
linearity requirements. The resulting loss in the
signal path degrades system NF, therefore, a second
LNA is needed after the filter to scale down the
noise of the following circuit.
Building Blocks Design 3.1 LNA1 Design
The first LNA (LNA1) must meet
simultaneous low noise and high linearity. A
single-ended topology with two amplifier stages is
chosen to fulfill the gain, linearity requirements and
minimize the number of external components. Fig.
2 shows the simplified schematic of LNA1. The
designed LNA1 is composed of two
common-emitter stages with inductive emitter
degeneration, mainly realized with the bonding
wires to the bonding pads.
LNA2 Design
The LNA2, as shown in Fig. 3, provides a high
gain mode amplifying the weak RF signal to
increase the receiver sensitivity and a low gain
mode attenuating the strong RF signal and easing
the linearity requirements for the following blocks.
Quadrature Mixers Design
the double-balanced Gilbert cell
down-conversion mixer. The bipolar input devices
are properly chosen because of its good noise
performance.
[attachment=22745]
Introduction
The wide-band code division multiple access
(WCDMA) standard has been developed by the
Third Generation Partnership Project as a standard
for next generation digital mobile phone
applications [1]. The WCDMA standard achieves
higher data rates, channel capacity, and more
efficiency than current 2G systems.
Direct Conversion Receiver Architecture
In direct conversion topology, there is no
significant filtering of RF signals outside the
receiving band before the mixer and baseband
circuitry except in the duplexer, and the most
serious signal may come from Tx leakage. These
lead to high linearity requirements, which burden
the system. In the implemented receiver this work,
as shown in Fig. 1, an external interstage filter is
inserted after the LNA1 to provide additional Tx
and out-of-band attenuation and thus relaxes the
linearity requirements. The resulting loss in the
signal path degrades system NF, therefore, a second
LNA is needed after the filter to scale down the
noise of the following circuit.
Building Blocks Design 3.1 LNA1 Design
The first LNA (LNA1) must meet
simultaneous low noise and high linearity. A
single-ended topology with two amplifier stages is
chosen to fulfill the gain, linearity requirements and
minimize the number of external components. Fig.
2 shows the simplified schematic of LNA1. The
designed LNA1 is composed of two
common-emitter stages with inductive emitter
degeneration, mainly realized with the bonding
wires to the bonding pads.
LNA2 Design
The LNA2, as shown in Fig. 3, provides a high
gain mode amplifying the weak RF signal to
increase the receiver sensitivity and a low gain
mode attenuating the strong RF signal and easing
the linearity requirements for the following blocks.
Quadrature Mixers Design
the double-balanced Gilbert cell
down-conversion mixer. The bipolar input devices
are properly chosen because of its good noise
performance.