Chapter 3 MOSFETs Noise Coefficients Extraction
3.3 Conclusions
We have developed a new microstrip line design to measure NFmin accurately without the need for complicated de-embedding. Based on the accurate NFmin measurement and analytical NFmin equation, close agreements to the measurements with modeling data are all obtained that is important for further circuit application.
IV. UWB LNA Design
4.1 Introduction
Ultra wideband (UWB) systems are a new wireless technology capable of transmitting data over a wide spectrum of frequency bands with very low power and high data rates. Among the possible applications, UWB technology may be used for imaging systems, vehicular and ground penetrating radars, and communication systems. Although the UWB standard (IEEE 802.15.3a [16]) has not been completely defined, most of the proposed applications are allowed to transmit in a band between 3.1 and 10.6 GHz. In this work, the design of a low noise amplifier (LNA) in a 0.18µm CMOS technology for the receiver path of a UWB system is discussed. Such an amplifier must feature wide-band input matching to a 50Ω antenna, flat gain over the entire bandwidth, good linearity, minimum possible noise figure and low power consumption.
In recent years, narrow-band CMOS LNA designs have employed inductive source degeneration to achieve good input matching. This technique also yields nearly optimal noise figure at the resonance frequency of the input network [17]. In the proposed wide-band design in Figure 16 (at the next section), the inductively degenerated common source topology is further explored. The input impedance Zin is embedded in a two-section band-pass filter to resonate its reactive part over the whole
band. The cascode configuration improves the reverse isolation and the frequency response of the amplifier. Source-follower buffer of the second stage is intended for measurement purposes, i.e. to drive an external 50Ω load.
4.2 Design Procedures
In this work, we first use inductive source degeneration to achieve good matching to 100Ω in stead of the conventional 50Ω to decrease the Q value of the serial resonance circuits. This is because that the lower Q value implies the wider bandwidth, which makes a broadband matching. Then we add an L-section circuit to transfer the 100Ω to the source impedance 50Ω. Finally by using CAD tool to optimize the circuits, we can achieve an input reflection coefficient to smaller than -10dB in-band: Ls=0.9nH, Lg=1.6nH, L1=0.9nH and C1=0.25pF. The size of M1 is chosen as 128 gate fingers to minimize the inductance values. The bias of M1 is set for balance between gain and power consumption.
The cascode device is chosen as small as possible to reduce the parasitic capacitances. A lower limit to the width of M2 (24 gate fingers) is set by its reasonable Vds. Both M1 and M2 are minimum length devices. The load is designed to achieve flat gain over the whole bandwidth. In-band, M1 acts as a current amplifier, the input current being Vin/Rs, and the current gain β(ω)=gm/(jωCgs). To compensate
for the roll-off of β(ω), a shunt-peaked load is used. The value of the inductance L2 (2.3nH) is limited by acceptable power gain over shooting. Resistance RL (60Ω) improves the gain at lower frequency. All the design and the layout are shown in figure 18 and figure 19 respectively.
M1 M2
M3
M4
Ls Lg
L1 C1
RL
L2
L3 M1
M2
M3
M4
Ls Lg
L1 C1
RL
L2
L3
Figure 18 Circuits diagram.
Figure 19 Chip layout.
4.3 Simulation results
Figure 20 shows the simulated input and output reflection coefficients. S11 is lower than -8dB between 3.1 and 12GHz. The output buffer achieves excellent matching such that S22 is lower than -10dB from 1.7GHz to 15.9 GHz. Figure 21 is the power gain versus frequencies, and the maximum power gain is 10.4dB in our simulation results. Since the output source follower drives a matched load, the voltage gain of the core amplifier is exactly 6dB higher than S21. The -3dB bandwidth is 0.4~9.9GHz for the simulation. The noise figure (NF) of this UWB LNA is shown in Figure 22. The noise figure is as low as 3.3dB at 6GHz which is the center frequency
of UWB system, while the average noise figure in-band is about 4dB. Figure 23 and 24 show the simulated reverse isolation S12 and stability factor respectively. The two-tone test results for third-order intermodulation distortion are shown in Figure 25.
The test is performed at 6GHz. IIP3 is to 3.3dBm, and the input referred 1-dB compression point (ICP) is -9dBm. These results imply excellent linearity of our LNA.
The proposed UWB LNA dissipate 27mW (15mW for first stage) with a power supply of 1.8V. Figure 27 summarizes the performance of the presented amplifiers,
m2freq=
dB(S(1,1))=-7.9563.100GHz m3 freq=
dB(S(1,1))=-8.1787.900GHz m4 freq=
dB(S(1,1))=-13.06710.60GHz
2 4 6 8 10 12 14 16 18
0 20
-20 -15 -10 -5
-25 0
freq, GHz
dB(S(1,1))
m2 m3
m4
dB(S(2,2))
Figure 20 Simulated S11 & S22.
m1 freq=
dB(S(2,1))=7.884 3.600GHz m5 freq=
dB(S(2,1))=10.427 7.500GHz
2 4 6 8 10 12 14 16 18
0 20
0 10
-10 20
freq, GHz
dB(S(2,1))
m1 m5
Figure 21 Simulated power gain.
m6 freq=
nf(2)=3.326 6.100GHz
2 4 6 8 10 12 14 16 18
0 20
5 10 15 20
0 25
freq, GHz
nf(2)
m6
NFmin
Figure 22 Simulated NF and NFmin.
2 4 6 8 10 12 14 16 18
0 20
-100 -80 -60 -40
-120 -20
freq, GHz
dB(S(1,2))
Figure 23 Simulated reverse isolation.
2 4 6 8 10 12 14 16 18
0 20
2 3 4 5
1 6
freq, GHz
Mu1MuPrime1
Figure 24 Simulated stability.
Figure 25 Two tones test.
Figure 26 Power-out versus power-in.
m1 Pin=
dBm(out[::,1])=-0.044 -9.000
-70 -60 -50 -40 -30 -20 -10 0
-80 10
-60 -40 -20 0
-80 20
Pin
dBm(out[::,1])
m1
m1indep(m1)=
plot_vs(dBm(out), freq)=-70.1116.000E9 m2indep(m2)=
plot_vs(dBm(out), freq)=-236.7515.950E9
5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4
5.5 6.5
-300 -250 -200 -150 -100
-350 -50
freq, GHz
dBm(out)
m1
m2
EqnIIP3=(m1-m2)/2-80 indep(IIP3)
<invalid>
IIP3 3.320
27; 15
Figure 27 Simulated circuits SPEC summary.
4.4 Measurements and Conclusions
The following figures 28~33 are the measurement results which are only slightly different form our simulation, which imply good accuracy of our simulation and good circuit design. The some of the bandwidth compression showing in figure 28 maybe due to the underestimate of the load resistor parasitic.
0 2 4 6 8 10 12 14 16 Figure 28 Measured power gain.
0 1 2 3 4 5 6 7 8 9 10 0
5 10 15 20
NOise Figure (dB)
Frequencies Figure 29 Measured noise figure.
0 2 4 6 8 10 12 14 16
-20 -15 -10 -5 0
S11 S-parameters (dB) S22
Frequencies Figure 30 Measured S11 and S22.
0 2 4 6 8 10 12 14 16 -50
-40 -30 -20 -10 0
S12
S-parameters (dB)
Frequencies Figure 31 Measured S12.
-30 -25 -20 -15 -10 -5 0
-80 -70 -60 -50 -40 -30 -20 -10 0 10
OP1 Output Power (dB) OP3
Input Power (dB) Figure 32 Measured linearity.
Figure 33 Measured results summary.
The bandwidth of this work with considering matching and power gain is from 3 to 8 GHz, while the average power gain is about 8dB which can be up to 14 dB without the current buffer in real cases. The noise performance is good and the minimum noise figure is only 3.5dB at 3~4GHz. The noise figure can be even better if we solve the bandwidth compression problem from the resistor parasitic. Input and output matching are achieved well in band and the linearity of this work is excellent.
Total power consumption is 27mW, while the core LNA consumes only 15mW by 1.8V power supply. By the new input matching approach we proposed, a low noise, broadband, low power consumption and good-linearity amplifier is developed for the UWB system applications.
+2
Figure 34 Die photo.
Figure 35 Comparison of broadband LNA performance.
0.18μm 2004
V. Summary
Let us summary the conclusions of this paper briefly.
Noise modeling: The low noise amplifier in a RF receiver is a significant component, since it plays an important role in the noise performance of a RF system, which affects the dynamic range and the signal to noise ratio of this system. The current noise model with BSIM3v3 core can not model the noise behavior correctly. In order to develop the accurate noise model of RF MOSFETs, we have developed a new microstrip line design to measure NFmin accurately without the need for complicated de-embedding. Based on the accurate NFmin measurement and analytical NFmin equation, close agreements to the measurements with modeling data are all obtained that is important for further circuit application.
UWB LNA: By the new input matching approach we proposed, a low noise, broadband, low power consumption and good-linearity amplifier is developed for the future UWB system applications. The advantages of this design include extending the famous source L-degenerate matching to broadband, low noise, low power consumption, reducing inductor numbers and excellent linearity. All the advantages are important for UWB system considerations.
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學經歷
姓名：賴照民 性別：男
出生年月日：民國七十年四月一日 籍貫：台北市
學歷：台北市立建國高中 (85 年 9 月~88 年 6 月)
國立交通大學電子工程學系 (88 年 9 月~92 年 6 月)
國立交通大學電子工程所 (92 年 9 月~94 年 6 月)
論文題目：
新穎的金氧半電晶體雜訊模型與應用於超寬頻系統低雜訊放大器之設計 Novel Noise Modeling of RF MOSFETs and the Design of an UWB LNA with Modified L-degenerate Input Matching