Low Flicker-Noise and Low Leakage Direct Conversion CMOS
Mixer for 5GHz Application
H. Kanaya1, N. Koga, M. A. Abdelghany, R. K. Pokharel, and K. Yoshida
Graduate School of Information Science and Electrical Engineering Kyushu University
744, Motooka, Fukuoka, 819-0395, Japan
1
kanaya@ed.kyushu-u.ac.jp
Abstract — This paper presents the design and measurement
of low flicker-noise, high conversion gain double-balanced
Gilbert cell mixer in CMOS process. Since the noise figure (NF)
of the CMOS mixer is strongly affected by flicker noise (1/f
noise), a dynamic current injection technique is used to reduce
the flicker noise corner frequency. An inductor is employed to
tune the tail capacitance in the local oscillator and the RF
transconductance stages. So, it reduces the RF leakage through
this parasitic capacitance. Moreover, output band elimination
filter (BEF) is employed to suppress the leakage of the RF signal.
The mixer is designed using TSMC 0.18 μm CMOS process.
Simulations and measurements had been performed. The
proposed mixer has a simulated conversion gain of 15dB and
single side band noise figure is 10.6dB at 20kHz.
Index Terms — CMOS mixer, Gilbert cell mixer, flicker-noise,
band elimination filter.
I. INTRODUCTION
In recent years, development of the single chip transceivers
to minimize cost, power dissipation and chip size are
necessary for wireless communication systems. Direct
conversion receiver (DCR) is one of the best candidates for
low complexity, low power, and low cost single chip
integration [1]. Unfortunately, all of these advantages come
with the fact that the CMOS transistors suffer from a very
high intrinsic flicker noise [2]. Linear RF circuits don’t
affected by the flicker noise, such as low noise amplifiers
(LNA), since its operating frequency is much higher than the
flicker noise corner frequency [3], but in the mixers, the case
is different, because the flicker noise lies in the output band
of the mixer, specially, low-IF and Zero-IF mixers.
There are a lot of designs to reduce the output flicker noise
of the mixer. Static current injection has been proposed in
[4]. Dynamic current injection technique with a shunt tuning
inductor has been designed in order to reduce the effect of
tail capacitance at the node between the local oscillator (LO)
switches and RF transconductance stage for 2.4GHz
applications [5,6]. Also, in our previous study, differential
active inductor is employed instead of the tuning spiral
inductor in the Gilbert cell mixer for 5GHz application [7].
In this paper, we have proposed a mixer circuit composed
of PMOS switches as current injecting circuit, inductor which
is employed to tune the tail capacitance, and output band
elimination filters (BEFs) which suppress the RF leakage. As
a result, the flicker noise reduction occurred, at the same time,
we can suppress the RF leakage. Simulation results verified
that this design has good performances compared to other
designs. Also, we fabricated and measured the proposed
mixer by using 0.18 μm CMOS process.
II. MECHANISM OF THE FLICKER NOISE IN GILBERT CELL MIXER
There are two major mechanisms that generate the flicker
noise. One is the direct mechanism and another is indirect
mechanism. Direct mechanism is due to the finite slope of
the switching pair transitions. In order to decrease a flicker
noise in the direct mechanism, the size of the switching pairs
needs to be increased, however, large switching devices
increase the parasitic capacitance of the switching pairs,
resulting in the flicker noise translating to the output. The
second, indirect mechanism is due to the tail capacitance at
the node between the LO switches and RF transconductance
stage [2].
In order to decrease the flicker noise in CMOS active
mixers, the bias current of the LO switches should be small
enough to lower the height of the noise pulses. The static
current injection technique was proposed to reduce the bias
current of the LO switches [4]. However, the impedance of
the LO switches as seen from the RF stage is increased as we
reduce the bias current of the LO switches.
The dynamic current injection technique has also been
proposed in [5-7] to suppress the flicker-noise. It injects a
dynamic current totally equal to the bias current of the LO
switches at only the LO switching event [3].
In addition, RF leakage current flows through the injection
circuit, which decreases conversion gain and also allows
more RF current to be shunted by the tail capacitance at the
node between the LO switches and RF transconductance
stage. The tail capacitance should be minimized to decrease
the indirectly translated flicker noise [2]. To minimize the tail
capacitance, a smaller device size is appropriate for the LO
switches, which increases the flicker noise from direct
mechanism. The parallel tuning inductor compensates the
parasitic tail capacitance.
III. MIXER DESIGN
A. Design of proposed Gilbert cell mixer
Fig. 1 shows the comparison of the circuit model of the
proposed and static current injection Gilbert cell mixer,
respectively. Both mixers have a tuning inductor. In order to
reduce the direct and indirect flicker-noise generation,
dynamic current injection technique using three PMOS
switches near Vb and VDD [5,6], as shown in Fig.1 (a).
These PMOS switches inject a dynamic current equal to the
bias current of each pair of switches at only the switching
event. Vb is used to control the height of the injected current
pulses.
Vb
Vb
LO+
and third is the proposed Gilbert mixer with dynamic current
injection.
VDD
VDD
LO+ LO+
LO-
RF+
LO+
LO-
RF-
RF+
RF-
(a)
Vb
tuning inductor
Fig. 1. Comparison of the circuit model of the dynamic (a) and
static (b) current injection Gilbert cell mixer, respectively.
B. Design of out put band elimination filter (BEF)
In order to suppress the leakage of the RF signal in the
base band output port, two band elimination filter (BEF)s,
which composed of ladder connection of inductors and
capacitors, are connected on the both output ports (Out+ and
Out-), respectively. Fig.2 shows the final circuit model of the
proposed Gilbert cell mixer with output BEFs.
(b)
Out+
VDD
Vb
Out-
LO+
LO-
LO+
Band elimination filters
RF+
RF-
Fig. 3. Output power versus frequency of the proposed Gilbert cell
mixer without (a) and with output BEF (b).
conventional
With Static Current Injection
With Dynamic Current Injection
Fig. 2. Circuit model of the dynamic current injection Gilbert cell
mixer with BEFs.
IV. SIMURATION RESULTS
The proposed mixer in Fig. 2 is designed by TSMC
0.18μm 1P6M CMOS technology, and simulated by Cadence
and Agilent tools. The input RF and LO frequencies are
5.2GHz and 5.1GHz, respectively, to obtain 100MHz base
band frequency.
Fig. 3 shows the output power versus frequency of the
proposed Gilbert cell mixer without and with output BEFs.
Output signal of proposed mixer at 5.1GHz is 28.4dB smaller
than that of the mixer without BEFs. We can suppress the
5GHz-band signal, namely RF leakage, by using on chip BEF.
Fig. 4 shows simulation results of the noise figure (NF) for
three configurations of Gilbert mixer, one is the conventional
mixer, second is the Gilbert-cell with static current injection,
Fig. 4. Simulation results of the noise figure (NF).
In Fig.4, the NF of the proposed mixer is about 10dB at
1MHz, which is similar to that of the conventional mixer.
Also the flicker noise of the proposed mixer is better than
that of the static current injection mixer, and the proposed
mixer has a 20KHz flicker corner frequency. Fig. 5 and Fig.
6 show the input third orders intercept point (IIP3) and input
1-dB compression point (P1dB) of the proposed mixer,
respectively. The proposed mixer has IIP3 is -6.3dBm and
P1dB is -14.2dBm.
can obtain the base band signal and peak-to-peak value is
approximately 124mV.
+LO -LO
Matching
circuit
Output power [dBm]
+RF
BEF
BEF
Out-
Out +
Input power [dBm]
Tuning inductor
Fig. 7. Micrograph of the proposed Gilbert cell mixer.
Output power [dBm]
Fig. 5. Input third orders intercept point of the proposed mixer.
-RF
Input power [dBm]
Fig. 6. Input 1-dB compression point of the proposed mixer.
V. EXPERIMENTAL RESULTS
Fig. 7 shows the micrograph of the proposed Gilbert cell
mixer using TSMC 0.18μm 1P6M CMOS technology. The
total sizes with I/O pads is 1.1mm x 1.0mm. The matching
circuit and tuning inductor are also shown. The input
impedance of the RF is 50Ω. Differential RF inputs and LO
inputs are injected through the two GSG probes (Cascade
microtech.), which have 150μm pitch and 50Ω input
impedance, and GSGSG probe (Cascade microtech.), which
has 100μm pitch and 50Ω input impedance, respectively.
Also, output BEFs are shown near the output ports. Output
base band signal can be obtained though the bonding wires.
Fig. 8 shows the comparison of the measured and
simulated input return loss, respectively. This matching
circuit works at around 5GHz.
The input RF and LO frequencies are 5.2GHz and 5.1GHz,
respectively, to obtain 100MHz base band frequency. Fig. 9
shows the measured output signal of the proposed mixer. We
Fig. 8. Comparison of the simulated and measured return loss.
10ns/div
Fig. 9. Measured output waveform of the proposed mixer.
Table 1 shows a comparison of the proposed mixer with
the conventional mixer, the mixer with static current injection,
and the mixer with dynamic current injection. It shows that
the proposed mixer using dynamic current injection, inductor
and BEF has a good performance, specially, with a high
conversion gain and suppression of the flicker noise at
20KHz. Power consumption is the same as other mixers.
Table 1. Performance comparison of the proposed mixer
(simulation).
Direct
current
injection and
BEF
Conv.
Static current
injection and
BEF
15
6.8
13
Convesion
gain [dB]
NF at 20kHz
[dB]
P1dB[dBm]
10.6
21.4
12.1
-14.2
-11.8
-19.8
IIP3[dBm]
-6.3
-3.0
-10.1
Power
consumption
[mW]
10.8
10.8
10.8
VI. CONCLUSION
A Gilbert cell mixer using dynamic current injection,
inductor and output BEFs has been proposed and measured.
The proposed mixer is fabricated using TSMC 0.18μm 1P6M
CMOS technology, so that, the mixer operates under 1.8v
supply voltage. We can minimize the flicker noise sources
and RF leakage. The mixer has a 10dB NF at 1MHz, 10.6dB
at 20KHz and 15dB conversion gain, respectively. Also, it
has a 1-dB compression point of –14.2dBm, and IIP3 of 6.3dBm.
ACKNOWLEDGEMENT
This work was partly supported by a Grant-in-Aid for
Scientific Research from JSPS (KAKENHI) and Fukuoka
project in the Cooperative Link of Unique Science and
Technology for Economy Revitalization (CLUSTER) from
Ministry of Education, Culture, Sports, Science and
Technology (MEXT).
This work was also partly supported by VLSI Design and
Education Center (VDEC), the University of Tokyo in
collaboration with CADENCE Corporation and Agilent
Corporation.
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