
82 MICROWAVE JOURNAL APRIL 2011
Technical FeaT ure
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• <1 μsec Switching Speed
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Your compact high-performance
synthesizer solution
Your compact high-performance
synthesizer solution
spinnaker.ads_1/3 pg horz 3/17/11 12:33 PM Page 1
through the network, the impedance
should be transformed from Z
2
to the
exact conjugate match Z
1
*. However,
the transformed impedance is Z
T
,
whose difference from Z
1
* results
in mismatch loss that is exploited to
equalize the gain between the states.
Transformation to the high resistance
region of the Smith chart (E’) is also
necessary for minimum bandwidth.
5
In
addition to the transformation purpose,
the series capacitors (C
1
and C
4
) also
behave as DC blocking capacitors. The
shunt capacitor C
2
is realized by using
four shunt capacitors with FET switch-
es placed in series for frequency control.
Here, the center frequency switching
takes place by varying the capacitance
ance matching network used in the in-
terstage. This network has a bandpass
response. Impedance matching using
a Smith chart was used to determine
the initial components values.
Figure 2 shows the impedance
transformations used to reach the
high-Q contour on the Smith chart.
The series capacitor C
4
transforms the
input impedance of the second-stage
amplifier, Z
2
to A’. The shunt capacitor
C
3
then transforms A’ to B’, the series
inductor L
2
transforms B’ to C’, the
shunt capacitor C
2
transforms C’ to
D’, the shunt inductor L
1
transforms
D’ to E’ and finally the series capaci-
tor C
1
transforms E’ to Z
T
. Ideally,
to ensure maximum power transfer
Circuit Design and
Small-signal
Performance
The first step in the design is the
selection of the first- and second-stage
BJTs, including biasing and ballast net-
works, and input and output matching
for 1 to 2 GHz operation. This initial
design uses simple high-pass and low-
pass L-section matching networks for
the input and output. A blocking ca-
pacitor is used in the interstage and
some resistive loading is used to im-
prove stability. The output impedance
of the first-stage amplifier (Z
1
) and the
input impedance of the second-stage
amplifier (Z
2
) were then calculated.
Figure 1 shows the π-section imped-
s Fig. 3 Schematic diagram of M-probe for implementation in ADS.
MeasEqn
Meas1
Z1 = S42/S32
Z2 = S41/S31
R11 = real(Z1)
R22 = real(Z2)
M = 4*R11*R22/(abs(Z1+Z2)*abs(Z1+Z2))
M_dB = dB(M)2
VAR
VAR1
Z0 = 50
R1
R2
Term
Term4
Num = 4
Z = Z0 Ohm
Term
Term3
Num = 3
Z = Z0 Ohm
Term
Term2
Num = 2
Z = Z0 Ohm
R
R3
R = 1 MOhm
R
R2
R = 1 MOhm
R1
R2
VCVS
SRC2
G = 10
R1 = 1 MOhm
VCVS
SRC1
G = 0.1
R1 = 1 MOhm
R
R1
R = 0.01 Ohm
Port
P2
Num = 2
Port
P1
Num = 1
Term
Term1
Num = 1
Z = Z0 Ohm
+
–
+
–
+
–
–
+
–
+
+
–
Meas
Eqn
Var
Eqn
4M32 FINAL.indd 82 3/25/11 3:44 PM