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Design of Low Noise, High Dynamic Range and Triple-Band MMIC Voltage
Variable Attenuator Using 0.25 μm GaAs pHEMT Technology

Article · January 2024

DOI: 10.18485/mtts_mr.2024.30.1.9

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 Microwave Review
July 2024, Vol. 30, No. 1, pp. 67-74
DOI: 10.18485/mtts_mr.2024.30.1.9

Design of Low Noise, High Dynamic Range and Triple-

Band MMIC Voltage Variable Attenuator Using 0.25 μm
GaAs pHEMT Technology
Subham Banerjee1, Md Sujauddin Ahmmed, Arun Kumar Ray, Santanu Mondal

Abstract – This paper proposes the design of 1.2-1.3 GHz, 2.5-3 Attenuator (VVA) is of two types-absorptive VVA and
GHz and 5.4-5.8 GHz MMIC voltage variable attenuator (VVA) monolithic VVA. Source-controlled attenuator falls under the
realized using 0.25 µm GaAs pHEMT technology. It is a category of monolithic VVA. Although in Ref. [1], it is stated
wideband voltage variable attenuator as it covers entire radar that impedance variation is the primary cause for the non-
frequency bands. It provides a minimum attenuation of 2 dB in L
linear response of variable attenuators, we have leveraged this
and S-Band and 3 dB in C-Band and maximum attenuation of 72
dB in L-Band, 60 dB in S-Band and 47 dB in C-Band with impedance variation to achieve high dynamic range of
attenuation flatness of 3 dB in L and S-Band and 1 dB in C- attenuation, low insertion loss and good linearity. Voltage
Band. The phase response of the attenuator is also shown in this variable attenuators can find applications in automatic gain
paper. The attenuator is perfectly matched with source and load control circuits in radar receivers. In case of target-tracking
impedances. It shows full-band stability. By convention, noise radar, signal-to-noise ratio increases when the target comes
figure is equal to attenuation. The novelty of this proposed design into radar’s vicinity. This can cause the radar receiver to
is source controlled attenuator using gm-reduction and double saturate. To prevent saturation of radar receiver, voltage
active termination techniques with noise figure less than variable attenuator is employed to attenuate the signal,
attenuation. These techniques increase the dynamic range of
enabling further processing by the receiver. The most
attenuation and reduce noise figure also. The double active
termination technique also contributes in reducing noise figure common of the attenuators discussed in the literature are pi-
below each attenuation level. It is necessary to keep noise figure type, T-type and cascaded pi-T type attenuator [3]. A negative
below attenuation because the attenuator will be used in RF feedback voltage variable attenuator described in [4] gives a
front-end of radar receiver. By keeping noise figure below bandwidth of 0.4 GHz in C-Band. The proposed design has
attenuation, sensitivity of radar receiver will improve. Input 1 dB better stability (> 5) compared to that of [4] which has
compression point of the proposed attenuator at maximum stability >1. A variable attenuator designed in [5] gives an
attenuation are at -4.3 dBm in L-Band, -5.9 dBm in S-Band and insertion loss of 6 dB and dynamic range of over 12 dB at 9-
-5.3 dBm in C-Band and OIP3 at minimum attenuation are at 15 GHz frequency. Most of the attenuators mentioned in the
-4.4 dBm in L-Band, -4.6 dBm in S-Band and -5 dBm in C-Band.
literature are gate-controlled configuration. Ref. [8] shows the
The ideal and post-layout simulation results are presented in this
paper. Figure of merit of the proposed attenuator is 280 in L- improvement of noise figure due to active termination. In the
Band, 70.3 in S-Band and 78.54 in C-Band. The attenuator can proposed design, gm-reduction technique and double active
be used in single target tracking radar as well as in T/R module termination are used to get noise figure which is very less than
of AESA radar. attenuation. The attenuator is properly matched with source
and load impedance. It is highly stable. The purpose of this
Keywords – Triple-band, Dynamic range, Insertion loss,
MMIC, Noise figure, Source-controlled. paper is to mark the importance of source-controlled voltage
variable attenuator, showing its inner working and shedding
light on the practical applications. The proposed design is a
I. INTRODUCTION source-controlled configuration with triple bandwidth, good
linearity, high dynamic range of attenuation, low insertion
The voltage-variable attenuator provides variable
loss and less noise figure as compared to attenuation. Section
attenuation depending on the control voltage applied. The
II describes the source-controlled attenuator. Section III
prime objective of voltage variable attenuator is to control the
highlights how dynamic range and noise figure is improved
signal strength [1]. An attenuator reduces input power by a
predetermined ratio [2]. Recently pHEMT based attenuator is using gm-reduction method and double active termination
used in automatic gain control applications due to its technique. Section IV and V highlights layout and post-layout
simulation results and its discussion. Section VI concludes the
capability of generating low noise. Voltage Variable
paper.
Article history: Received Month dd, yyyy; Accepted Month dd,
yyyy II. SOURCE-CONTROLLED ATTENUATOR
1
Subham Banerjee, Md Sujauddin Ahmmed and Arun Kumar Ray
are with the Integrated Test Range, Chandipur, India, E-mail: The MMIC layout is based on GaAs pHEMT technology
9088983569subham@gmail.com, md.sujauddin@gmail.com, using 0.25 µm pHEMT gate lengths. The MMICs are realized
drakroy.itr@gov.in on substrate, with two thick gold metallization levels, thin
Subham Banerjee and Santanu Mondal are with the Institute of film resistors, MESA resistor, MIM capacitors, spiral
Radio Physics & Electronics, Kolkata, India, E-mail: inductors and through the substrate via holes. The proposed
santanumondal2008@rediffmail.com circuit is miniature in size. This paper proposes the design of a

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Mikrotalasna revija Jul 2024

Fig. 1. Topology of triple-band attenuator

Fig. 2. pHEMT based equivalent circuit

1.2-1.3 GHz, 2.5-3 GHz and 5.4-5.8 GHz voltage variable TABLE 1
attenuator (VVA) realized using 0.25 µm pHEMT. The post- INTERNAL PARAMETERS OF PHEMT
layout simulation was carried out in Cadence AWR design
environment. Figure 1 shows the proposed circuit diagram of Internal parameters Values
L-, S- and C-Band attenuator. The operation of B1 is
governed by the control voltage applied to the source terminal
Ron 7.6 Ω
of B1 which increases the dynamic range of attenuation. The Gate-to-drain
0.87 fF
capacitance (Cgd)
input and output matching networks are used to improve the
Drain-to-source
input and output reflection coefficients respectively of the 28.5 fF
capacitance (Cds)
circuit. The internal parameters of the device are shown in
Table 1 [6] [7].

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July 2024 Microwave Review

III. DYNAMIC RANGE AND NOISE FIGURE g m 2 Rl 1  sRonCds 

AB 2   , (4)
IMPROVEMENT BY GM-REDUCTION AND 1  g m 2 Ron  sRonCds
DOUBLE ACTIVE TERMINATION TECHNIQUE
where gm2 is transconductance of B2, Rl can be expressed as
A. Gm-Reduction Technique follows:
 Ron   
The equivalent circuit [7] of the proposed attenuator is    
  Cds  r3  r4  50    
2
shown in Fig. 2. A GaAs MESFET or pHEMT is generally a Ron2 (5)
Rl      j  .
2
r  r  50  
 R 2   1  3 4   C  R 2   1   
2
field-controlled majority carrier device [2]. Here pHEMT
operates by the field introduced by the control voltage applied  on  C    ds  on  C   
to the source terminal of pHEMT. When control voltage is   ds      ds   
low (0.9 V), VGS is less negative and more than threshold
voltage, the device B1 turns on and the source current reaches r3 and r4 are resistors of output matching network. The
the load. When control voltage is high (2.2 V), VGS is highly input-referred noise Power Spectral Density [8] contributed by
negative and less than the threshold voltage, the device B1 B2 is calculated as follows:
turns off and there is no source current flowing through the
Vc2 g m 2 Ro22
circuit. The attenuation is given by Eq. (1). Vn2,in, B 2  4 KT . (6)
AB2 2
A  gm,eq Z0 , (1)
Ro2 is the output impedance of B2, Vc is the applied control
where gm,eq  gm1 / / gm 2 / / gm3 and gm1, gm2 and gm3 are voltage.
transconductances of B1, B2 and B3 respectively. The output
impedance is given in Eq. (2). Noise Voltage due to B3

Ron The attenuation due to B3 can be expressed as follows.

Cds g m3 Rl , B 3
Z . (2) AB 3   . (7)
  1 2  1  g m3 Req
 Ron     C  
2

 ds   gm3 is the transconductance of B3, Rl,B3 and Req can be

expressed as:
Here Zo=Z1+Z2+Z3, Z1, Z2 and Z3 are the output impedances of
   
2 Ron  
B1, B2 and B3 respectively. The transconductance of B1  
  Cds   
2
depends on source current which in turn depends on source  2 Ron2
voltage i.e. control voltage. At maximum attenuation, Rl , B 3   2 
 j  , (8)
   1   
 R2   1  
2

 Cds  Ron    
transconductance is low as compared to minimum attenuation
 on  C  
2
since source current is minimum at maximum attenuation. The   ds     Cds   
transconductance decreases with increase in attenuation. Due   
to this gm reduction and double active termination [8]
r3  r4  50 
techniques, noise figure is less than attenuation at minimum Req  . (9)
and maximum attenuation. The equation for the minimum r3  r4  50
noise figure is given in [9].
The input-referred noise Power Spectral Density [8]
Fmin  1  K f  ffT  gmeq  Rg  Rs   Ki , (3) contributed by B3 is calculated as follows:

where Rg and Rs are the gate and source resistances of Vc2 g m3 Ro23
pHEMT. Kf and Ki are fukui constants, gm,eq is the overall
Vn2,in, B 3  4kT . (10)
AB23
transconductance, f is the operating frequency, fT is the cutoff
frequency. As transconductance decreases, minimum noise Ro3 is the output impedance of B3.
figure also decreases.
Total Noise Voltage
B. Double Active Termination Technique
The total input-referred noise Power Spectral Density [8]
The proposed double active termination technique has been contributed by B2 and B3 is calculated as follows.
adopted to improve noise figure performance.
NVtotal  Vn2,in, B 2  Vn2,in, B3 . (11)
Noise Voltage due to B2
As per Fig. 6 of Section V, the noise figure is far below
It is formed by Ron-Cds parallel source degeneration as attenuation. It is due to gm-reduction technique and double
shown in equivalent circuit of the attenuator. The attenuation active termination technique. Double Active termination
can be expressed as:

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Mikrotalasna revija Jul 2024

Fig. 3. Layout of the L, S and C-Band attenuator (layout size-979.2 μm x 442.3 μm)

technique reduces noise voltage more than the active

termination technique.

IV. LAYOUT AND POST-LAYOUT SIMULATION

The attenuator has been designed using WIN 0.25 μm
pHEMT technology. In this process MIM capacitors, TFR and
MESA resistors are available, which are used in this design.
The layout occupies an area of 979.2 μm x 442.3 μm. The
current consumption is maximum during minimum Fig. 4. Plot of transconductance with control voltage
attenuation. The layout was carried out by connecting the
lumped elements with the microstrip lines. Microstrip tee
junction was used when there was a node connecting three
branches. After layout, post-layout simulation was carried out
and results are obtained. The post-layout simulation was
carried out using 3D Axiem simulator. It was used for
electromagnetic simulation of the microstrip lines.
Electromagnetic simulation also considered the parasitic
effects.

V. RESULTS AND DISCUSSION

The transconductance decreases with increase in
attenuation. During maximum attenuation, the
transconductance is less as compared to the transconductance Fig. 5. Plot of attenuation and noise figure with transconductance
during minimum attenuation. Due to this g m reduction
technique and active termination[8], noise figure is less than
attenuation at minimum and maximum attenuation. The plot
of attenuation and noise figure against transconductance is
shown in Fig. 4.
The transconductance decreases at maximum attenuation as
shown in Fig. 4 and hence noise figure is less than or equal to
attenuation. Fig. 5 shows that at each level of attenuation,
noise figure is less than attenuation which is our primary
requirement. In order to improve SNR and sensitivity of
receiver, it is required to keep the noise figure below
attenuation. The plot of attenuation and noise voltage with
control voltage is shown in Fig. 6.
Fig. 6. Plot of attenuation and noise voltage with control voltage

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July 2024 Microwave Review

As per Fig. 6, the noise figure is far below attenuation. It is attenuation flatness are 3 dB in L and S-Band and 1 dB in C-
due to gm-reduction technique and double active termination Band. The phase of S21 with varying control voltage is shown
technique. Double Active termination technique reduces noise in Fig. 9. The insertion phase variation are 1.7 0 in L-Band, 50
voltage more than the active termination technique. in S-Band and 40 in C-Band.

A. Minimum and Maximum Attenuation

The post-layout simulation results show that the

performance of attenuator is undeviating from the ideal
behavior. The novelty of the circuit is low insertion loss, high
dynamic range of attenuation and less noise figure as
compared to attenuation. In this section, Vc is an abbreviation
for control voltage. The minimum attenuation is 2 dB. The S-
curve of the attenuator follows the following path.

Fig. 9. Phase of S21 for varying control voltage

Input and output reflection coefficients are better than -10

dB. The input and output reflection coefficients at all the
states are less than -10 dB. Fig. 10 shows the plot of reflection
coefficients in the required frequency bands. The proposed
attenuator is a triple-band design where S11 and S22 are much
below -10 dB in the required frequency band.

Fig. 7. Plot of attenuation with control voltage

The dynamic range of attenuation is approximately 70 dB

in L-Band, 58 dB in S-Band and 44 dB in C-Band. The
minimum attenuation of 2 dB occurs at a control voltage of
0.9 V in L and S Band and 3 dB in C-Band and maximum
attenuation of 72 dB and 60 dB in L and S-Band and
maximum attenuation of 47 dB in C-Band. The attenuation
flatness is 3 dB in L, S-Band and 1 dB in C-Band.

Fig. 10. Input and output reflection coefficients of the triple-band

attenuator at control voltage ranging from 0.9 V to 2.2 V
(blue-S11 and pink-S22)

Fig. 8. Plot of attenuation of triple-band attenuator at control voltage

ranging from 0.9 V to 2.2 V

The dynamic range of attenuation is approximately 70 dB

in L-Band, 58 dB in S-Band and 44 dB in C-Band. The Fig. 11. Plot of attenuation and noise figure at minimum and
maximum attenuation

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Mikrotalasna revija Jul 2024

As the voltage variable attenuator will be used in front-end D. Linearity Analysis

of radar receiver along with Low Noise Amplifier, it is
important to keep the noise figure below attenuation. By Two important parameters for determining linearity of a
doing so, sensitivity of receiver will improve. The noise figure circuit are 1 dB compression point and input intercept point of
corresponding to minimum attenuation of 2 dB is 0.01 dB in order 3 (Fig. 14). At maximum attenuation, input 1 dB
L-Band, 0.2 dB in S-Band whereas in C-Band, it is 0.6 dB compression point are at -4.3 dBm in L-Band, -5.9 dBm in
which corresponds to a minimum attenuation of 3 dB. S-Band and -5.3 dBm in C-Band and OIP3 (Fig. 15) at
Similarly, at maximum attenuation, noise figure is less than or minimum attenuation are at -4.4 dBm in L-Band, -4.6 dBm in
equal to attenuation as shown in Fig. 11. S-Band and -5 dBm in C-Band.
The proposed attenuator shows relatively better
B. Group Delay performance than previous mentioned works. The proposed
attenuator can be used in ground station radar, operating in L-
The proposed attenuator gives a group delay of less than 0.1 Band, S-Band and C-Band for effectively tracking of the
ns across 0.1 GHz span in 1.2-1.3 GHz, 2.5-3 GHz and 5.4- target. The source-controlled attenuator gives low insertion
5.8 GHz (Fig. 12). The group delay variation is less than 0.1 loss, high dynamic range of attenuation and less noise figure
ns at minimum and maximum attenuation levels. as compared to attenuation which is not present in the
literature. Though the dynamic range is very high, up to 30 dB
of maximum attenuation is considered because in this range,
the phase of S21 varies between -500 to +500. FOM of the
proposed attenuator is 280 in L-Band, 70.3 in S-Band and
75.84 in C-Band. Table 2 shows the performance comparison
of the proposed design with the other works in the literature.
The proposed design outperforms the performance of the
existing gate-controlled attenuator in the literature as shown in
Table 2.

Fig. 12. Group delay variation at minimum and maximum

attenuation

C. Stability Analysis

The proposed design is stable across 0.1 GHz span in

1.2-1.3 GHz, 2.5-3 GHz and 5.4-5.8 GHz at all values of
control voltage (Fig. 13). At control voltage of 0.9 V, the
stability factor (k-value) at 2.8 GHz is greater than 9 and at Fig. 14. Plot of 1 dB compression point of the proposed triple-band
attenuator
5.6 GHz it is greater than 6. At other control voltages, the
stability factor (k-value) is higher than 10.

Fig. 15. Plot of OIP3 of the proposed triple-band attenuator

Fig. 13. Plot of stability factor (k-value) with frequency for different
values of control voltage

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July 2024 Microwave Review

VI. CONCLUSION input and output reflection coefficients were less than -10 dB
for entire range of control voltage. The OIP3 was found to be
The proposed design gives a large dynamic range with less -4.4 dBm in L-Band, -4.6 dBm in S-Band and -5 dBm in C-
noise figure as compared to attenuation, low insertion loss and Band. Though the dynamic range is very high, we will
good linearity. The total occupied area was about 0.4312 mm2 consider up to 30 dB because in this range, the phase of S21
and the current consumption was about 8 mA during varies between -500 to +500. Characterizing with large
minimum attenuation. Dynamic range is enhanced and noise dynamic range, miniature size, low insertion loss and less
figure is greatly reduced by applying the method of gm- noise figure as compared to attenuation, the attenuator can be
reduction and double active termination techniques. The used in single target tracking radar and T/R module of AESA
dynamic range of attenuation achieved was about 70 dB and radar.

TABLE 2
COMPARISON OF SOURCE-CONTROLLED ATTENUATOR WITH THE EXISTING GATE-CONTROLLED ATTENUATOR

Ref. Topology Frequency Minimum Maximum Reflection Area Noise FOM

attenuation attenuation coefficient Figure
[10] Local 26-30 GHz N/A Attenuation N/A N/A - -
feedback Range-18
dB
[11] - 10-14.4 N/A Attenuation < -11 0.7 mm2 - -
GHz range-22
dB
[12] Switched 2-20 GHz N/A Attenuation < -9 1.725 mm2 - -
path and T range-31.5
w/ active dB
switch
[13] - 0.06 GHz N/A Attenuation N/A 0.1 mm2 - -
range-48
dB
[14] - DC-3.7 0.9-1.25 ~37 dB < -10.6 dB 0.27 mm2 - 1.42
GHz
[15] - 0.4-3.7 2.1 dB 33 dB < -9 dB - - 25.35
GHz
This work 1 Stage 1.2-1.3 2 dB & 3 72 dB, 60 << -10 dB 0.4312 <= 280 in L-
attenuator GHz, 2.5-3 dB dB & 47 mm2 attenuation Band, 70.3
with gm- GHz & 5.4- dB in S-Band
reduction 5.8 GHz and 78.54
and double in C-Band
active
termination
[3] W. Cheng, M. S. Oude Alink, A. J. Annema, G. J. M. Wienk and
B. Nauta, “A Wideband IM3 Cancellation Technique for
ACKNOWLEDGEMENT CMOS Π- and T-Attenuators,” in IEEE Journal of Solid-State
Circuits, vol. 48, no. 2, pp. 358-368, Feb. 2013.
The work is supported by Integrated Test Range and
University of Calcutta. I like to thank Director of Integrated [4] M. S. Ahmmed, S. Banerjee, A. K. Ray and R. K. Chaudhury,
Test Range, Shri H. K. Ratha, Additional Director of Radar “Design of MMIC Voltage Variable Attenuator for T/R Module
Division, Dr. Niladri Roy and Group Director of Radar of Phased Array Radar, ” 2nd International Conference on
Division, Shri N. Biswal for providing me the opportunity to Range Technology (ICORT), Chandipur, Balasore, India, 2021,
do this work. pp. 1-4,
[5] R. Teja N., P. Verma, A. Kumar and A. N. Bhattacharya, “A
Dual-Band High Linearity Voltage Variable Attenuator
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