CMOS wifi

1. See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/286529994
CMOS WiFi RF Front-Ends for Mobile Handset Applications. Part-1: Preserving
WCDMA Receiver Sensitivity.
Technical Report · March 2012
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2. White Paper
CMOS WiFi RF Front-Ends for Mobile
Handset Applications
Part-I: Preserving WCDMA Receiver Sensitivity
WiFi RF Front-Ends from RFaxis based on bulk CMOS silicon technologies can greatly
improve performance of a mobile handset.
Oleksandr Gorbachov
RFaxis, Inc. March 2012

3. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 2
Contents
Introduction…………………………………………………………………………………………..3
Background…………………………………………………………………………………………..3
Test Setup………………………………………………………………………………………….....8
Noise Measurement Results………………………………………………………………………….9
Conclusions…………………………………………………………………………………………..13
Figures
Fig.1. Basic architecture of a typical WCDMA mobile handset with WLAN connectivity………...3
Fig.2. Spectrums in WCDMA-WiFi mobile handset………………………………………………..4
Fig.3. Noise contributions at WiFi TX output………………………………………………………5
Fig.4. WLAN RF Front-End in details……………………………………………………………...7
Fig.5. Test bench for total noise measurements……………………………………………………..8
Fig.6. CMOS RF Front-End total transmit noise in the WCDMA receive band at the antenna pin
(50-Ohm input and BPF input connection to signal source). Signal generator modulation noise at
WCDMA receive band is rejected to a level <-180dBm/Hz…………………………………….......9
Fig.7. Total transmit noise in the WCDMA receive band at the antenna pin for various technologies
(50-Ohm input connection to 2.4GHz signal source). Signal generator modulation noise at the
WCDMA receive band is rejected to a level <-180dBm/Hz……………………………………….10
Fig.8. Total transmit noise in the WCDMA receive band at the antenna pin for various technologies
(BPF and 50-Ohm input connection to signal source). Signal generator modulation noise at the
WCDMA receive band is rejected to a level <-180dBm/Hz……………………………………….10
Fig.9. Total transmit noise in the WCDMA receive band at the antenna pin for bulk CMOS, GaAs
HBT and PHEMT technologies (50-Ohm input connection to signal source). Signal generator
modulation noise at the WCDMA receive band is rejected to a level <-180dBm/Hz......................11
Fig.10. Total transmit noise in the WCDMA receive band at the antenna pin for BiCMOS SiGe
HBT technology (50-Ohm input connection to signal source). Signal generator modulation noise at
the WCDMA receive band is rejected to a level <-180dBm/Hz…………………………………..12
Fig.11. WCDMA receiver NF degradation due to the RF Front-End developed on various
technologies (50-Ohm input connection to signal source). Signal generator modulation noise at the
WCDMA receive band is rejected to a level <-180dBm/Hz. Co-existence filter-1 at the antenna side
rejection is selected at 25dB and isolation between antennas is 15dB………………………….....13

4. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 3
Introduction
This document presents test results for comparison of noise contributions from different WLAN
power amplifiers and front-end modules in the WCDMA receive band-1 (2.11GHz to 2.17GHz)
from multiple tier-1 vendors developed on different technology processes including bulk RF
CMOS, BiCMOS SiGe HBT, GaAs HBT, and PHEMT.
Background
Market demand for radio-frequency (RF) Wireless Local Area Network Power Amplifiers
(WLAN PAs) and Front End Modules (FEMs) continues to expand year after year. Performance,
size, and cost are driving forces enabling demand in this market segment. Especially challenging is
the mobile phone application of a WLAN system in which the WLAN will operate in a very
crowded RF environment. At the same time, mobile phone manufacturers desire to exploit as many
possible functions in their handsets as possible. One of these features is the simultaneous operation
of a cellular network voice call while searching the internet or down-loading data files through a
WLAN network. Some cellular systems such as UMTS use a communication protocol with the
transmitter and receiver always on. In this case the requirement of the spur or noise signal
transmission by the on-board WLAN transceiver is stringent even when those systems are
operating at different frequencies. Due to the small, compact design of mobile handsets, antenna
positioning for different communication standards is possible only in close proximity to each other.
Baseband and other types of noise from a WLAN system should not degrade cell-phone receiver
operation through overloading or desensitization.
TX
RX
RF Front-End
PA-1
ANT-1
ANT-2
1
2
3
LNA-1
LNA-2
Duplexer
TX_ON
WCDMA
Transceiver
RF_TX
RF_RX
Co-exist
Filter-1
SPDT
1
2
3
PA-2
TX_ON
WLAN
Transceiver
RX
TX
RX_ON
RX_ON
Co-exist
Filter-2
RF_RX
RF_TX
TX
RX
RF Front-End
PA-1
ANT-1
ANT-2
1
2
3
LNA-1
LNA-2
Duplexer
TX_ON
WCDMA
Transceiver
RF_TX
RF_RX
Co-exist
Filter-1
SPDT
1
2
3
PA-2
TX_ON
WLAN
Transceiver
RX
TX
RX_ON
RX_ON
Co-exist
Filter-2
RF_RX
RF_TX
TX
RX
RF Front-End
PA-1
ANT-1
ANT-2
1
2
3
LNA-1
LNA-2
Duplexer
TX_ON
WCDMA
Transceiver
RF_TX
RF_RX
Co-exist
Filter-1
SPDT
1
2
3
PA-2
TX_ON
WLAN
Transceiver
RX
TX
RX_ON
RX_ON
Co-exist
Filter-2
Co-exist
Filter-2
RF_RX
RF_TX
Fig.1. Basic architecture of a typical WCDMA mobile handset with WLAN connectivity
Fig.1 presents the RF part of a typical WCDMA handset architecture with WLAN connectivity.
The WLAN system uses a TDD (time domain duplex) communication protocol utilizing a SPDT

5. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 4
(single-pole/double-throw) RF switch to connect the antenna to a TX or RX chain in separate time
intervals. For WLAN, the TX and RX frequencies are the same in each channel.
The WCDMA system utilizes FDD (frequency domain duplex) communications protocol. For
this technology, a duplexer is used to connect an antenna simultaneously to a TX and RX chain at
different frequencies.
Although the WLAN frequency band (2.4GHz – 2.5GHz) is more than 200MHz away from the
highest WCDMA receive band-1 (2.11GHz – 2.17GHz) and other WCDMA receive bands are
positioned even further away, WLAN transmit signals contain wide spread spectrum “shoulders”
(due to phase noise, modulation spectrum contributions, etc.), and these shoulders fall into the
WCDMA receive band (see Fig.2).
Typical antenna isolation between WLAN and WCDMA antennas of 15dB to 20dB reduces to
some extent the signal level from a WLAN TX reaching a WCDMA antenna, but the signal level is
still too large which can significantly degrade the WCDMA receiver sensitivity.
Thermal Noise
Floor at Antenna
(-174dBm/Hz)
F, GHz
P
Wideband noise from WCDMA TX
signal at input of WCDMA receiver
(due to duplexer)
WLAN TX signal at
ANT2(Burst)
WCDMA TX signal at
ANT1(Continuous)
In-band added Noise from
WLAN TX signal
WLAN TX signal at input of
WCDMA receiver (due to
distance between antennas
and their gain)
WCDMA RX Band
Fig.2. Spectrums in WCDMA-WiFi mobile handset
For reference, the additional noise power level added to the thermal noise floor in the WCDMA
receiver input with a level of 6dB below the thermal noise floor elevates the total noise in the
receiver input by 1dB, thus degrading sensitivity by 1dB.
The typical duplexer used in a WCDMA system on the antenna side allows the WCDMA TX
signal level at the receiver input to be well below -174dBm/Hz to avoid degrading sensitivity.
Therefore, the added noise power level from a WLAN system during transmit mode should be in
the range of -180dBm/Hz to get the WCDMA receiver sensitivity degradation below 0.5dB. Please
note that this degradation level also depends on the receiver Noise Figure (NF) which will be
discussed in more details. The typical requirements for a multi-mode handset with WCDMA and
WLAN systems specify degradation of the receive sensitivity for WCDMA system of no more than

6. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 5
0.5dB to 1.0dB while the WLAN system is in operation.
To define proper filtering characteristics, it is necessary to know the noise power levels for the
WLAN TX output. This noise consists of three main parts; 1) The internal noise of the TX chain, 2)
The output noise due to the modulation process, and 3) The noise from the transceiver amplified
through the TX chain at a particular frequency (see Fig.3).
Thermal Noise
Floor at Antenna
F, GHz
P, dBm/Hz WLAN TX signal
at ANT2 (Burst)
Noise “shoulders” from WiFi
transceiver at input of WLAN PA
WLAN TX signal at input
of PA/RF Front-End
(from WiFi transceiver)
WCDMA RX Band
Noise “shoulders” at PA output
with CW signal at input (due to
phase noise and internal PA NF)
Noise “shoulders” at PA output
with modulated signal at input
(due to phase noise, internal PA
NF and due to modulation)
Noise “shoulders” reject
from DSG used in test bench
-174
Thermal Noise
Floor at Antenna
F, GHz
P, dBm/Hz WLAN TX signal
at ANT2 (Burst)
Noise “shoulders” from WiFi
transceiver at input of WLAN PA
WLAN TX signal at input
of PA/RF Front-End
(from WiFi transceiver)
WCDMA RX Band
Noise “shoulders” at PA output
with CW signal at input (due to
phase noise and internal PA NF)
Noise “shoulders” at PA output
with modulated signal at input
(due to phase noise, internal PA
NF and due to modulation)
Noise “shoulders” reject
from DSG used in test bench
-174
Fig.3. Noise contributions at WiFi TX output
Filtering has become a very important and difficult issue in multi-mode handsets. With a WLAN
system operating in a WCDMA handset, it has become necessary to include a co-existence filter
(typically bulky LTCC) to maintain minimum degradation of the WCDMA receiver chain
sensitivity, which adds cost, increases PCB footprint, and degrades the performance of the WLAN
system by increasing current consumption and decreasing sensitivity.
A novel filtering technique has recently been developed via implementing the co-existence filter
inside the power amplifier chain (typically at its input) to mitigate requirements for external
filtering (see co-exist filter-2 in Fig.1). However, on-die implementation of a full performance co-
existence filter so far could not be accomplished due to the fairly low Q-factors of on-die
components, which also requires the use of an external co-existence filter on the antenna side. It is
also important to note that for most semiconductor technologies, a high level of rejection at the
input of the PA does not help to avoid a large noise signal level at the PA output. This noise can be
due to internal noise generation, modulation noise, cross-modulation, etc. As described in details
below, only the bulk-CMOS based circuits developed at RFaxis, when combined with a high level
of rejection at the PA input, can result in a substantially mitigated requirement for filtering at the
antenna side.
A co-existence filter is typically specified as a band-pass filter which will additionally reject
unwanted spectrum emissions such as harmonic frequencies while the WLAN TX chain is active.

7. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 6
This in turn introduces additional loss into the WLAN TX and RX chains thus degrading their
performance. As higher levels of rejection for co-existence frequencies are needed, higher insertion
loss is added in-band, and these high levels of rejection also result in higher filter cost.
Many existing solutions implement a moderate level of rejection at the co-existence frequencies
for the filter on the antenna side (co-existence filter-1), with moderate filter cost, while additional
filtering is implemented at the input of the TX WLAN RF chain front-end (co-existence filter-2).
This is typically a cost-effective solution with less degradation of the RF parameters for the WLAN
system. Typical insertion loss of the co-existence filter-1 is 2.0dB to 3.0dB. This requires the
WLAN power amplifier (PA-2) to have a higher output power level, resulting in higher current
consumption from the battery and decreases sensitivity of the WLAN receive chain by the same
amount, which adversely impacts the link distance and data throughput for the WLAN
communication system.
The PA output noise contribution due to transceiver noise is directly proportional to the gain in
the 2.11GHz to 2.17GHz frequency band; with a lower gain in this band there will be a lower noise
contribution (the input co-existence filter-2 is very useful in this case). With a lower PA Noise
Figure in the 2.11GHz to 2.17GHz band, the internal noise contribution will also be lower at the PA
output at small signal levels.
The noise “shoulders” for the PA output due to modulation are highly dependent on process
technology and PA circuit design, including input, output, and inter-stage matching networks, in-
band gain, transducer phase compression curvature, cross-modulation products due to self-mixing,
baseband frequency impedance at particular circuit nodes, etc.
Consider the architecture of a PA with a band-pass filter (BPF) at the input for simplicity (Fig.4).
A PA is typically treated as a separate block which is characterized by its input and output
impedance over a frequency range while matched to a certain external impedance (i.e. 50-Ohm for
wireless communications and connectivity standards).
A BPF is also specified by its input and output impedance over a frequency range while both
ports are matched to a particular impedance (i.e. 50-Ohm). While this impedance may be close to
the specified impedance for in-band frequencies, it could be much higher or much lower at out-of-
band frequencies, and it is not purely resistive. Filtering is typically done through the use of
reactive components (i.e. capacitors, inductors, transmission lines, etc.) implemented in various
configurations.
The main delusion during consideration of this type of circuit operation at a system level is the
assumption that an external filter results in only out-of-band rejection, thus reducing gain at these
frequencies, and noise performance of the PA at these frequencies is not changed due to the
impedance mismatch. In reality, a PA contains one or more active elements such as the FET
transistor as shown in Fig.4, and its noise performance depends greatly on the matching conditions
at particular frequencies. This particular filtering characteristic should be carefully considered
while keeping in mind the internal structure and broadband characterized performance of the PA
with proper signal levels and modulation applied.

8. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 7
PORT
0
1
1
2
3
SPDT
AMP
Power Amplifier
Low Noise Amplifier
Coexistence Filter
SPDT
ON-OFF Control
Bias Supply
DC
RF
RF
&
DC
1 2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
(-)
NEG2
BPFB
PORT
PORT
1
2
3
FET
(-)
NEG2
BPFB
1
2
3
FET
Input Filter
Input
Match
Output
Match
Inter-stage
Match
Control
Block
Bias
Block
Input
Match
Z1_in(RF)
Z1_in(BB)
Z2_in(RF)
Z2_in(BB)
Z_IN
Z_OUT
Z1_out
Z2_out
Z_IN(TX)
Z_OUT(BPF) Z_ANT
TX
RX
ANT
PORT
0
1
1
2
3
SPDT
AMP
Power Amplifier
Low Noise Amplifier
Coexistence Filter
SPDT
ON-OFF Control
Bias Supply
DC
RF
RF
&
DC
1 2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
(-)
NEG2
BPFB
PORT
PORT
1
2
3
FET
(-)
NEG2
BPFB
1
2
3
FET
Input Filter
Input
Match
Output
Match
Inter-stage
Match
Control
Block
Bias
Block
Input
Match
PORT
0
1
1
2
3
SPDT
AMP
Power Amplifier
Low Noise Amplifier
Coexistence Filter
SPDT
ON-OFF Control
Bias Supply
DC
RF
RF
&
DC
1 2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
DC
RF
RF
&
DC
1
2
3
BIASTEE
(-)
NEG2
BPFB
PORT
PORT
1
2
3
FET
(-)
NEG2
BPFB
1
2
3
FET
Input Filter
Input
Match
Output
Match
Inter-stage
Match
Control
Block
Bias
Block
Input
Match
Z1_in(RF)
Z1_in(BB)
Z2_in(RF)
Z2_in(BB)
Z_IN
Z_OUT
Z1_out
Z2_out
Z_IN(TX)
Z_OUT(BPF) Z_ANT
TX
RX
ANT
Fig.4. WLAN RF Front-End in details
It is well known that FETs (and other types of transistors as well) with a particular size and bias
condition require an optimum impedance provided by the input matching circuit to get the
minimum level of noise for a PA output. This noise power is frequency dependent and the greater
the mismatch between required optimum and actual impedance presented at the gate, the greater the
level of noise power at the output of the PA.
In-band noise power for the PA output can be defined by the typical approach which uses Noise
Figure related calculations when impedances are close and don’t very much. When impedance
mismatch is high, the standard Noise Figure approach is not accurate enough to predict the correct
PA output noise power, and this is usually the case when the input circuit contains a high rejection
level filter. The out-of-band impedance may differ from the in-band impedance (i.e. 50-Ohm) by a
factor of several tens or even hundreds, and output noise power could be much higher than
estimated by the system designer. This PA could introduce a much higher noise power at out-of-
band frequencies of interest including the WCDMA receive band or the GPS band while the
WLAN is transmitting. Gain at the out-of-band frequencies may also change in the presence of a
large in-band signal, resulting in the out-of-band noise power amplified at a different gain level.
Cross-correlation of mixed-signal products in out-of-band frequencies further complicates the
analysis. Other very important noise sources are biasing/control circuits which may introduce a
high level of noise while a modulated signal is passing through the PA.
For instance, if a very high level of rejection at the WCDMA receiver band is implemented by
means of an input filter (see Fig.4), noise contributions from inter-stage, output, and biasing and
control circuits may prevail and a high rejection filter at the antenna side will still be needed.
Typically, during the system integration process, the above mentioned parameters are not fully
known for a system design which may result in the expenditure of much time and effort to achieve

9. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 8
the desired performance. The integrated solution developed at RFaxis will require much less effort
for system designers to integrate the WLAN RFeIC into a WCDMA handset.
Test Setup
A test bench setup is presented in Fig.5. The Digital Signal Generator (DSG) is used to provide a
modulated 54Mbps OFDM WLAN signal at different frequencies and power levels. A band-pass
filter (BPF) is used at the DSG output to reject wide-band and modulation noise at the WCDMA
receive frequencies well below -174dBm/Hz level. A 10dB attenuator is used between the BPF and
the PA/RFeIC transmitter input. This represents a typical case for a real application with the
WLAN transmitter connected to PA/RFeIC without the co-existence filter-2 (see Fig.1). In the case
when an additional filter-2 is used, the test bench replicates this setup by removing the attenuator.
Output of the PA (antenna pin of RFeIC) is connected through a 3dB splitter to a spectrum/signal
analyzer, which is used to present 50-Ohm impedance at the PA/RFeIC output. The mismatch
introduced by 2.11GHz to 2.17GHz BPF between the splitter and spectrum/signal analyzer, which
is used to prevent spectrum analyzer overdrive, could substantially change the operation of the
PA/RFeIC. The other port of the splitter is used for WLAN signal EVM measurement at PA/RFeIC
output. Integrated power measurements for a 5MHz channel ,which is equal to WCDMA channel
bandwidth, is used in the spectrum analyzer for noise power measurement with further division to
dBm/Hz. Proper de-embedding to the PA/RFeIC package pin reference plane is used.
Spectrum/
Signal
Analyzer
3dB Splitter
PA
BPF
2.11…2.17
GHz
DSG
(WiFi)
Reject wideband noise of
DSG at WCDMA receive
frequencies at PA Input
Protect Spectrum Analyzer
from overdriving at WiFi
frequencies
50ohm
BPF
2.4…2.5GHz
Protect PA output from
changing impedance due to
BPF (2.11…2.17GHz) insertion
ATTN
10dB
Keep 50-Ohm impedance
looking from PA Input to
Signal Source
(could be used or omitted)
This port of Splitter is used
for EVM measurements
Spectrum/
Signal
Analyzer
3dB Splitter
PA
BPF
2.11…2.17
GHz
DSG
(WiFi)
Reject wideband noise of
DSG at WCDMA receive
frequencies at PA Input
Protect Spectrum Analyzer
from overdriving at WiFi
frequencies
50ohm
BPF
2.4…2.5GHz
Protect PA output from
changing impedance due to
BPF (2.11…2.17GHz) insertion
ATTN
10dB
Keep 50-Ohm impedance
looking from PA Input to
Signal Source
(could be used or omitted)
This port of Splitter is used
for EVM measurements
Spectrum/
Signal
Analyzer
3dB Splitter
PA
BPF
2.11…2.17
GHz
DSG
(WiFi)
Reject wideband noise of
DSG at WCDMA receive
frequencies at PA Input
Protect Spectrum Analyzer
from overdriving at WiFi
frequencies
50ohm
BPF
2.4…2.5GHz
Protect PA output from
changing impedance due to
BPF (2.11…2.17GHz) insertion
ATTN
10dB
Keep 50-Ohm impedance
looking from PA Input to
Signal Source
(could be used or omitted)
This port of Splitter is used
for EVM measurements
Fig.5. Test bench for total noise measurements

10. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 9
Noise Measurement Results
Fig.6 presents total noise power measurement results for RFaxis’ RFeIC. Three frequencies are
used for the WLAN 54Mbps OFDM transmit signal while noise power is measured at 2.11GHz and
2.17GHz at the PA output connector. The highest noise power in the WCDMA receive band is
-140dBm/Hz at WLAN transmit power levels up to +20dBm, and has negligible dependence on the
50-Ohm connection to the signal source or via the BPF at the input of the PA. A 2dB/dB slope of
noise power over WLAN transmit power at some frequencies could be seen at high transmit signal
levels if the PA input is connected to a transceiver output through a high rejection filter (see dashed
line in Fig.6).
CMOS RF Front-End Noise in WCDMA Receive Band (54Mbps OFDM Transmit)
-145
-144
-143
-142
-141
-140
-139
-138
-137
-136
-135
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Pout, dBm
Total
Noise,
dBm/Hz
50o hm_input
2.4GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.44GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.48GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
B P F _input
2.4GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.44GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.48GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
Fig.6. CMOS RF Front-End total transmit noise in the WCDMA receive band at the antenna
pin (50-Ohm input and BPF input connection to signal source). Signal generator modulation
noise at WCDMA receive band is rejected to a level <-180dBm/Hz.
Fig.7 and Fig.8 present total noise power measurement results for various semiconductor
technologies. Either one or three frequencies are used for the WLAN 54Mbps OFDM transmit
signal while noise power is measured at 2.11GHz and 2.17GHz at the PA output connector. A 50-
Ohm connection to the signal source is used as well as via the BPF at the input of the PA. Wide
variation of noise power is obvious for different devices. 0.5dB/dB to 2dB/dB is the typical slope
for noise power in a WCDMA receive band over transmit power for all technologies except CMOS
(see dashed lines in Fig.7 and Fig.8).
Detailed comparison of the different technologies is presented in the figures below.

11. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 10
Fig.7. Total transmit noise in the WCDMA receive band at the antenna pin for various
technologies (50-Ohm input connection to 2.4GHz signal source). Signal generator
modulation noise at the WCDMA receive band is rejected to a level <-180dBm/Hz.
Fig.8. Total transmit noise in the WCDMA receive band at the antenna pin for various
technologies (BPF and 50-Ohm input connection to signal source). Signal generator
modulation noise at the WCDMA receive band is rejected to a level <-180dBm/Hz.
Noise in WCDMA Receive Band (50-Ohm 2.4GHz 54Mbps OFDM Transmit)
-143
-141
-139
-137
-135
-133
-131
-129
-127
-125
-123
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Pout, dBm
Total
Noise,
dBm/Hz
RFaxis_CMOS_FE
2.17GHz
2.11GHz
SiGe_HBT_PA_#1
2.17GHz
2.11GHz
SiGe_HBT_PA_#2
2.17GHz
2.11GHz
SiGe_HBT_PA_#3
2.17GHz
2.11GHz
GaAs_HBT_PA_#1
2.17GHz
2.11GHz
GaAs_HBT_PA_#2
2.17GHz
2.11GHz
GaAs_HBT_PA_#3
2.17GHz
2.11GHz
GaAs_HBT_PA_#4
2.17GHz
2.11GHz
GaAs_PHEMT_PA
2.17GHz
2.11GHz
Noise in WCDMA Receive Band (54Mbps OFDM Transmit)
-145
-143
-141
-139
-137
-135
-133
-131
-129
-127
-125
-123
-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Pout, dBm
Total
Noise,
dBm/Hz
GaAs_HBT _P A
2. 4GHz_i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 44GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 48GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
RFaxi s_CM OS_FE
2. 4GHz_i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 44GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 48GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
Si Ge_HBT _P A_#1
2. 4GHz_i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 44GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 48GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 4GHz_i nput _50ohm
2. 17GHz _noi se
GaAs_HBT _P A
RFaxi s_CM OS_FE
Si Ge_HBT _P A_#1
Si Ge_HBT _P A_#2
Si Ge_HBT _P A_#2
2. 4GHz_i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 44GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se
2. 48GHz _i nput
2. 17GHz _noi se
2. 11GHz _noi se

12. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 11
Fig.9 presents total noise power measurement results for RFaxis’ RFeIC and a GaAs HBT
(device with lowest noise power level chosen among others) and GaAs PHEMT PA. Three
frequencies are used for the WLAN 54Mbps OFDM transmit signal while noise power is measured
at 2.11GHz and 2.17GHz at the PA output connector. The lowest noise power in the WCDMA
receive band is -134dBm/Hz for GaAs based circuits at power levels up to +20dBm while the
CMOS based RFeIC provides noise power below -140dBm/Hz. These values are used below for
the WCDMA receiver sensitivity degradation calculations.
GaAs HBT and PHEMT circuits generate at least 6dB higher noise power levels in comparison
to the CMOS solution. It is worth noting that GaAs based circuits show substantial elevation of
noise power in the WCDMA receive band with the increase of WLAN transmit power level
(0.5dB/dB to 1dB/dB is a typical slope – see dashed lines in Fig.9). At the same time, GaAs based
circuits have a large variation of noise power over WLAN transmit frequencies as well as over
receive frequency offsets used during the test.
RFaxis’ CMOS RFeIC presents a totally different noise power behavior. Generated noise power
in the CMOS device shows low variations over the frequency band and transmitter power levels.
Moreover, noise power in WCDMA receive band is declining with the rise of transmit power levels
up to and above +20dBm.
Fig.9. Total transmit noise in the WCDMA receive band at the antenna pin for bulk CMOS,
GaAs HBT and PHEMT technologies (50-Ohm input connection to signal source). Signal
generator modulation noise at the WCDMA receive band is rejected to a level <-180dBm/Hz.
Fig.10 presents the total noise power measurement results for three different PA devices based
on SiGe HBT technologies (three different foundries, processes, circuits, and vendors). Three test
TX Noise in WCDMA Receive Band (54Mbps OFDM Transmit)
-143
-142
-141
-140
-139
-138
-137
-136
-135
-134
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Pout, dBm
Total
Noise,
dBm/Hz
R F axis_C M OS_F E
2.4GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.44GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.48GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
GaA s_H B T _P A _# 1
2.4GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.44GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.48GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
GaA s_P H EM T _P A
2.4GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.44GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut
2.48GH z_input_signal
2.17GH z_no ise_o ut
2.11GH z_no ise_o ut

13. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 12
frequencies are used for the WLAN 54Mbps OFDM transmit signal while noise power is monitored
at 2.11GHz and 2.17GHz at the PA output connector. Note that the highest frequency offset
between the WLAN transmit signal and the WCDMA receive band does not necessarily result in
the lower noise power. The best noise power in the WCDMA receive band is -129dBm/Hz among
the three part numbers at power levels up to +20dBm. This value is used for the WCDMA receiver
sensitivity degradation calculations below. SiGe HBT tested devices present at least a 5dB higher
noise power level in comparison to GaAs HBT and PHEMT presented above.
SiGe HBT PA Noise in WCDMA Receive Band (54Mbps OFDM Transmit)
-139
-138
-137
-136
-135
-134
-133
-132
-131
-130
-129
-128
-127
-126
-125
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Pout, dBm
Total
Noise,
dBm/Hz
SiGe_H B T _P A _# 2
2.4GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.44GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.48GH z_input
2.17GH z_no ise
2.11GH z_no ise
SiGe_H B T _P A _# 1
2.4GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.44GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.48GH z_input
2.17GH z_no ise
2.11GH z_no ise
SiGe_H B T _P A _# 3
2.4GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.44GH z_input
2.17GH z_no ise
2.11GH z_no ise
2.48GH z_input
2.17GH z_no ise
2.11GH z_no ise
Fig.10. Total transmit noise in the WCDMA receive band at the antenna pin for BiCMOS
SiGe HBT technology (50-Ohm input connection to signal source). Signal generator
modulation noise at the WCDMA receive band is rejected to a level <-180dBm/Hz.
Fig.11 presents the WCDMA receiver Noise Figure degradation as a result of the WLAN
transmitter noise addition while different PA/FEM technologies are tested. 25dB of co-existence
filter-1 (see Fig.1) rejection is chosen which may provide a moderate level of in-band loss, and
isolation between the antennas is 15dB. A typical WCDMA receiver in a mobile handset may have
a total Noise Figure of 3dB to 5dB which includes the duplexer and antenna switching circuitry
loss.
Based on the test data presented, it can be observed that the RFaxis’ RFeIC based on bulk CMOS
technology introduces just 0.3dB to 0.5dB loss to the WCDMA receiver sensitivity.
Under the same conditions, the GaAs HBT and PHEMT based PA/FEM used in WiFi TX chain
resulted in 1.2dB to 1.8dB sensitivity degradation for the WCDMA receiver. This level of loss may
be suitable for low-end phones while high-end phones will require at least 30dB of rejection for the
co-existence filter.

14. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 13
A co-existence filter with 25dB of rejection cannot be used with the SiGe HBT based PA/FEM
circuits as the 3dB to 4dB degradation of a receiver’s sensitivity cannot be tolerated by the
WCDMA handset. 30dB of co-existence filter rejection should be used in low-end phones while at
least 35dB of rejection should be used in a high-end phone.
Co-existence filters with 25dB and 35dB of rejection typically differ by 1.0dB to 1.5dB of in-
band loss. Therefor a CMOS based WLAN RF front-end circuit would require 1.0dB to 1.5dB less
linear power output at the PA, decreasing current consumption as well as increasing the receiver
sensitivity for the WLAN system by the same amount.
These conclusions are based on PA/FEM devices commercially available from various vendors.
Fig.11. WCDMA receiver NF degradation due to the RF Front-End developed on various
technologies (50-Ohm input connection to signal source). Signal generator modulation noise
at the WCDMA receive band is rejected to a level <-180dBm/Hz. Co-existence filter-1 at the
antenna side rejection is selected at 25dB and isolation between antennas is 15dB.
Conclusions
• The total output noise in a WCDMA receive band of a multi-mode handset from the WiFi
TX chain consists of three distinctive parts: 1) Noise from WLAN transceiver amplified
through PA/FEM TX chain; 2) Internal noise of the PA/FEM (thermal noise and phase
noise); and 3) Modulation noise due to the non-linearity of the PA/FEM.
• Cross-modulation products inside the PA/FEM chain provide different contributions to the
total output noise. A “simple” Gain/Noise Figure budget simulation will not provide correct
noise power levels at the output of the PA/FEM in a WCDMA receive band while the input
WCDMA Receiver NF Degradation (25dB Co-exist Filter)
-6.5
-6
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0 1 2 3 4 5 6 7 8
WCDMA Receiver NF, dB
NF
Degradation,
dB
RFaxis_CMOS
GaAs_HBT_and_PHEMT
SiGe_HBT

15. CMOS WiFi RF Front-Ends for Mobile Handset Applications – Part-I 2012
Page 14
is driven by a WiFi OFDM signal at high power level.
• RF CMOS based circuits used in RFaxis designs present the lowest noise power at the
output of the PA or RFeIC in the WCDMA receive band (2.11GHz to 2.17GHz) compared
to other known technologies while a 54Mbps OFDM signal is used – at least 6dB lower
noise power compare to GaAs HBT and PHEMT solutions and 11dB lower compare to
SiGe HBT based circuits.
• Total noise power in WCDMA receive band depends on WLAN transmit power level at a
rate of 0.5dB/dB to 2.0dB/dB, with elevating noise level at large power, for all technologies
except for bulk CMOS which has either unchanged or even slightly reduced noise power at
large WLAN signal levels.
• The co-existence filter between the antenna and RFaxis’ RFeIC could be chosen with lower
rejection which immediately results in lower in-band loss. This is beneficial to the WiFi
receiver sensitivity, as well as to extending the battery life due to minimized WLAN
transmitter chain loss.
• With a 25 dB rejection co-existence filter at the antenna side, a properly configured
complete solution based on RFaxis’ CMOS RFeIC will only degrade the sensitivity of the
WCDMA receiver by less than 0.3dB to 0.5dB. This is a perfect solution for both high-end
and low-end mobile handsets.
• GaAs HBT and PHEMT based PA circuits degrade WCDMA receiver sensitivity by 1.2dB
to 1.8dB for the same 25dB rejection co-existence filter, which is suitable only for use in
low-end mobile phones. For high-end phones, co-existence filter rejection should be
increased at least above 30dB. This would degrade the WiFi receiver sensitivity and will
increase current consumption of the transmit chain.
• SiGe HBT based PA circuits degrade WCDMA receiver sensitivity by 3dB to 4dB for a co-
existence filter with 25dB of rejection, which is unacceptable for a mobile phone. For low-
end phones, filter rejection should be increased at least above 30dB, while in high-end
phones the minimum rejection should be above 35dB. Both of these solutions will degrade
to a high extent the WiFi receiver sensitivity. Moreover, current consumption of the WiFi
transmit chain will be increased by more than ten percent which will adversely impact
battery life.
• CMOS based WLAN RF front-end circuits from RFaxis (RFeIC) require 1.0dB to 1.5dB
less linear power at the PA output (with accordingly decreased current consumption) as well
as improved receiver sensitivity for the WLAN system by the same amount.
• The particular issues of WiFi receiver sensitivity as well as minimizing co-existence filter
rejection and in-band loss with additional co-existence filter implementations at the input of
the WLAN transmit chain will be discussed in Part II and Part III of this White Paper.
RFaxis, Inc.
7595 Irvine Center Drive, Suite 200
Irvine, California 92618
www.rfaxis.com
Tel.: 949.336.1360
Fax: 949.336.1361
Email: marketing@rfaxis.com
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