Indian Journal of Science and Technology, Vol 9(26), DOI: 10.17485/ijst/2016/v9i26/97253, July 2016
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Design of a Broadband HEMT Mixer for UWB
Applications
Ehsan Ehsaeyan*
Sirjan University of Technology, Sirjan, Kerman, Iran; ehsaeyan@sirjantech.ac.ir
Abstract
Background/Objectives: Microwave mixer is a crucial element in virtually all transmits and receives systems. Methods/
Statistical analysis: In this paper, a novel distributed HEMT mixer with three layers is designed for Ultrawide-Band
(UWB) receivers. We employ external capacitors in the proposed circuit to adjust the output phase shift between stages to
equal the input phase shift. Findings: The simulation results show that the proposed structure, achieves vary ­broadband
­performances in Converstion Gain, Power Consumption and LO-RF Isolation, comparable to the recent reported cascode or
dual-gate distributed mixers. With a local oscillator power of 12 dBm and RF power of -20 dBm, our mixer has a Conversion
Gain of 0 ~ 4 dB (without IF signal amplification), LO-to-RF isolation better than 32 dB and 130 mW DC power consumption
over bandwith 5-25 GHz. Applications/Improvements: In our scheme, an intermediate layer is considered to increase
LO-RF Isolation and improve the Converstion Gain criterion. Moreover, Microstrip lines are used to form the artificial gate
and drain transmission lines as well as phase equalization of the signal on drain transmission line.
Keywords: Distributed Mixer, HEMT Mixer, Millimeter-Wave (MMW), Ultra-Wideband, Wireless Communication
1. Introduction
Microwave receivers for advanced EW systems are being
improved, requiring the development of broad bandwidth. So far the concept of distributed circuit has offered
attractive solution to some challenging problems in high
speed communication systems1.
Microwave mixer is a crucial element in virtually all
transmits and receives systems. The distributed mixer
offers wideband performance with low VSWR and flat
conversion gain characteristics.
Recently PHEMT technology in broad mixers has been
considered due to high cut-off frequency, low noise, high
gain and stronger nonlinearity in transconductance2.
A GaAs-based broadband mixer has been developed
using the distributed topology composed of cascode
FET cells which shows a high conversion gain of 3.6 dB,
but with high DC power consumption3. A 6-30 GHz
image-rejection mixer in SMT package has been built
and demonstrated4. The completed mixer showed -10 dB
typical conversion gain with 15 dB image-rejection ration
over band. One single traveling-wave MMIC for highly
*Author for correspondence
linear broadband mixers and variable gain amplifier is
present5. An integrated image-rejection mixer in a surface mount package for low cost 10-22 GHz applications
has been demonstrated6. A novel small-area distributed
mixer using multi-port inductors with conversion gain
of more than -10 dB for ultra wideband receivers is presented7. Recently, a broadband singly balanced distributed
mixer using the GaAs pHEMT process is developed over
a bandwidth from 4 to 41 GHz8.
In this paper the design of a new wideband distributed
architecture HEMT mixer is described. The proposed
UWB mixer has a good conversion gain without IF signal
amplification (comparable to the conversion gains of distributed mixers in the published literature), relatively low
DC power consumption and high LO-to-RF isolation.
2. Proposed Distributed Active
Mixer
The schematic of the proposed distributed mixer is shown
in Figure 1.
Design of a Broadband HEMT Mixer for UWB Applications
The distributed mixer uses the input Capacitance
of the transistor (Cgs) to construct a low pass filter with
lengths of transmission line forming the series inductance. The transmission line design is very important for
the distributed circuit design. Microstrip lines are used to
form the artificial gate and drain transmission lines, and
for phase equalization of the signal on drain transmission
line.
These transmission lines must have equal phase shifts
between the stages when the mixer operating as a downconverter with a low IF frequency. Equal phase shifts
yields a constant phase offset at the IF frequency which
allows the IF power to be summed by connecting the
drain node of stages together9.
The external Capacitors (Cp) are added to adjust the
output phase shift between stages to equal the input phase
shift. Since the gate capacitance is much more than that of
the drain, the phase velocity of the wave under the gate is
lower than the phase velocity of the drain.
The imbalance in the phase velocity leads to dispersion
and reflection. By achieving equal phase shift between the
stages on the source and drain line, the gain contribution of each is summed in phase along the drain line. By
adding external Capacitors (Cp), the phase velocity of the
drain approaches to similar value of the gate. For ideal
mixer operation the phase constants of the lines have to
fulfill the following equation to maximize the conversion
gain10.
b gate ( f LO )− b gate ( f RF
) = b drain ( f IF )
(1)
Figure 1. Circuit schematic of the proposed distributed
mixer.
2
Vol 9 (26) | July 2016 | www.indjst.org
Where β refers to phase velocity. The circuit was designed
using both linear and nonlinear analysis techniques. A
linear analysis was used to optimize the voltages of circuit
in order to achieve efficient equally distributed mixing
action. A nonlinear analysis, based on harmonic balance
method was used to predict to performance of the circuit
and to determine the optimum bias conditions.
The circuit operates by equally distributing a portion
of the incident LO signal at the gate of each transistor
(FHX04) as the signal travels along the gate line. A similar
effect occurs with the RF signal at the drain.
The RF and LO signals are applied on the left side.
The IF signal passes a filter at the output. The termination
load connected at the end of the artificial transmission
line was designed to match the characteristic impedance
of the artificial transmission lines to reduce the Voltage
Standing Wave Ratio (VSWR).
The MESFETs are biased for maximum conversion
gain. This optimum bias point is near pinch-off, where the
first derivative of gm has its maximum and the nonlinear
characteristics of drain-to-source current versus drainto-source voltage are used for frequency mixing. In drain
mixers, both LO power and IF output are directly ­combined
at the drain of a FET biased in the knee region11.
The IF signal is extracted from the drain through an
IF low-pass-filter to obtain RF to IF and LO to IF isolation
as well as port matching.
3. Simulation Results
The circuit shown in Figure 1 was simulated using Agilent
Advanced Design System (ADS) simulator. The performance of the circuit was first investigated over a wide
range of bias points, to study the operating modes of the
mixer and determine the optimum bias point. An iterative design procedure was used until the design variables
converged to give the best conversion gain for the mixer.
The performance characteristics of mixer can be divided
into five parameters: conversion gain, noise figure, return
loss, isolation and compression power at the RF input port.
The mixer exhibited good conversion gain of 0 ~ 4 dB
over the 5 to 25 GHz band as shown in Figure 2 with an IF
frequency of 70 MHz and the LO level of 12 dBm.
The conversion gain can be higher than this if LO
power is increased. In order to determine the optimum
driver LO power level, the conversion gains versus LO
power sweep is simulated. This simulation is plotted in
Figure 3 for an RF of 15 GHz and 70 MHz IF.
Indian Journal of Science and Technology
Ehsan Ehsaeyan
Figure 4 demonstrates the simulated noise figure
v­ ersus RF frequency. The mixer has 20-25 dB NF over the
entire 9 GHz bandwidth. Another simulation includes
the s-parameter characteristic to find out the matching
performance of the proposed mixer. The s-parameters are
plotted in Figure 5.
Figure 2. Conversion Gain versus RF frequency, of which
LO power is 10 dBm and IF frequency is fixed at 70 MHz.
Figure 4. Noise Figure versus RF frequency.
Figure 3. Simulated conversion gain versus LO power, of
which RF frequency is fixed at 15 GHz , and IF bandwidth
is 70 MHz.
A simulation of noise figure is presented. There is an
optimum number of stages which results in minimum NF.
The optimum number of stages depends on the circuit
parameters such as gate resistance, transconductance of
the RF tail current transistor and also the voltage swings
at the LO port12. The four stages MESFET mixer was simulated using the nonlinear program to predict the noise
figure. A tuned transmission line is used to optimize noise
figure and input match at the same time.
Vol 9 (26) | July 2016 | www.indjst.org
Figure 5. Simulated 1 dB compression power at the RF
input port.
Indian Journal of Science and Technology
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Design of a Broadband HEMT Mixer for UWB Applications
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Dynamic range of the mixer can be determined from
simulates of the RF signal 1 dB compression point (P-1)
for down-conversion using an IF of 70 MHz. Figure 6
shows simulated P-1 indicating more than -12 dBm input
port power.
The distributed mixer described in this paper is design
to operate as a down converter with a 10 to 80 MHz IF.
The swept IF response is shown in Figure 7 for a fixed
RF of 15 GHz and power set to -20 dBm. As shown in
this figure, the conversion gain is virtually constant for
IFs between 10 MHz and 80 MHz.
The simulated LO-to-RF isolation is shown in Figure 8
as a function of RF frequency with an LO power of 12
dBm and a -20 dBm RF input signal, indicating better
than 32 dB, when the IF port is terminated in 50 ohms.
The mixer exhibits good return losses at all three
ports. The simulation broad bandwidth RF and LO input
matched characteristics of the distributed circuit topology
are shown in Figure 9. As indicated in this figure, the LO
and RF return losses of distributed mixer are better than 1
dB and 6 dB over the entire pass band. The IF port is also
well matched over the IF bandwidth. Table 1 compares
the performance of the proposed down-converter mixer
with results from published the state-of-the-art wideband
HEMT mixer for comparison.
Figure 6. Simulated 1 dB compression power at the RF
input port.
Figure 8. Simulated results of isolation versus RF
frequency.
Figure 7. Simulated conversion gain versus IF frequency,
of which RF frequency is fixed at 5 GHz.
Figure 9. Simulated RF and LO return loss as a function of
RF frequency of proposed mixer. RF and LO power level is
fixed at -20 and 12 dBm, respectively.
Vol 9 (26) | July 2016 | www.indjst.org
Indian Journal of Science and Technology
Ehsan Ehsaeyan
Table 1. Performance comparison between
previously published work on wideband mixers and
the proposed mixer
RF
(GHz)
Conversion
Power
LO-RF
PLO
Gain
Consumption Isolation
(dBm)
(dB)
(mW)
(dB)
[4]
6 ~ 30
-10
-
--- > 20
10
[5]
5 ~ 39
-2 ~ -5
1100
-
5
[8]
4 ~ 41
3.5 ~ 8
100
19
10
[11]
3 ~ 33
-1 ~ -4
77
20
13
[2]
3 ~ 34
-3.4 ~ -6.7
6
19
15
0~4
130
--- > 32
12
This
5 ~ 25
Work
4. Conclusion
A 5-25 GHz distributed mixer was developed. The mixer
achieved a conversion gain of 0-4 dB, high LO-to-RF isolation better than 32 dB and a average power dissipation
130 mW over a very wide-band frequency, which is comparable with the given references. The simulation results
suggest that the proposed mixer is capable of realizing ultra
­wide-band RF receivers as well as measurement systems.
5. References
1. Hema N, Kidav JU, Lakshmi B. VLSI architecture for
­broadband MVDR beamformer. Indian Journal of Science
and Technology. 2015; 8(19):1–10.
2. Chiu CH, Liang KH, Chang HY, Chan YJ. A 3-34 GHz GaAs
PHEMT distributed mixer with low dc power consumption. IEEE Compound Semiconductor Integrated Circuit
Symposium (CSIC’06); San Antonio, TX. 2006. p. 73–6.
3. Ko W, Kwon Y. A GaAs-based 3-40 GHz distributed mixer
with cascode FET cells. IEEE Radio Frequency Integrated
Vol 9 (26) | July 2016 | www.indjst.org
Circuits (RFIC) Symposium, Systems Digest of Papers;
2004. p. 413–6.
4. Fujii K, Morkner H. A 6-30 GHz image-rejection distributed
resistive mmic mixer in a low cost surface mount package.
IEEE MTT-S International Microwave Symposium Digest;
2005. p. 37–40.
5. Kallfass I, Purtova T, Brokmeier A, Ludwig W, Schumacher
H. One single travelling-wave MMIC for highly linear
broadband mixers and variable gain amplifiers. IEEE
MTT-S International Microwave Symposium Digest; 2005.
p. 97–100.
6. Phan K, Fujii K, Morkner H, Rixon A. An integrated
low noise amplifier and image-rejection mixer in a surface mount package for low cost 10-22 GHz applications.
European Microwave Integrated Circuits Conference; 2006.
p. 122–5.
7. Yammouch T, Fukuda S, Yammouch T, Ito H. Small-area
CMOS RF distributed mixer using multi-port inductors.
Asaia and South Pacific Design Automation Conference
(ASPDAC’08); Seoul. 2008. p. 105–6.
8. Chang FC, Wu PS, Lei MF, Wang H. A 4–41 GHz singly
­balanced distributed mixer using GaAs pHEMT technology. IEEE Microwave and Wireless Components Letters.
2007; 17(2):136–8.
9. Howard TS, Pavio AM. A distributed 1-12 GHz ­dual-gate
FET mixer. IEEE MTT-S International Microwave
Symposium Digest; 1986. p. 329–32.
10. Tang OSA, Aitchison CS. A very wide-band microwave
MESFET mixer using the distributed mixing principle.
IEEE Transactions on Microwave Theory and Techniques.
1985; 33(12):1470–8.
11. Deng KL, Wang H. A 3-33 GHz PHEMT MMIC distributed
drain mixer. IEEE Radio Frequency Integrated Circuits
(RFIC) Symposium Digest of Papers; Seattle, WA, USA.
2002. p. 151–4.
12. Safarian AQ, Yazdi A, Heydari P. Design and analysis of an
ultrawide-band distributed CMOS mixer. IEEE Transactions
on Very Large Scale Integration (VLSI) Systems. 2005;
13(5):618–29.
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