lt5560 Linear Technology Corporation, lt5560 Datasheet - Page 16

• Manufacturer Part Number: lt5560
• Description: 0.01mhz To 4ghz Low Power Active Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5560
The following example demonstrates the design of a
lowpass impedance transformation network for a signal
input at 900MHz.
The simplifi ed input circuit is shown in Figure 5. For this
example, the input transformer has a 1:1 impedance ratio,
so R
input impedance is: R
reactance will be used as part of the impedance matching
network. The matching circuit consists of additional exter-
nal series inductance (L1 and L2) and a capacitance (C1)
in parallel with the 50Ω source impedance. The external
capacitance and inductance are calculated below.
First, calculate the impedance transformation ratio (n)
and the network Q:
Next, the capacitance and inductance can be calculated
as follows:
16
X
X
n =
L
Q =
X
C
L
EXT
1
1
S
C
= R
=
=
= 50Ω. From Table 2, at 900MHz, the differential
=
R
R
= X
L
ω •
S
L
R
(
L
2
Q
n 1
S
• Q = 24.7Ω
=
=
1
L
−
X
= 58 3 . Ω
– X
L
28 8
C
50
EXT
)
2
=
INT
.
=
3 03
0 858
U
=
=
.
= 14.9Ω
.
L
1 74
X
+ jX
2
.
pF
EXT
ω
U
INT
=
= 28.8 + j9.8Ω. The internal
1 32
.
W
nH
U
The internal inductance has been accounted for by subtract-
ing the internal reactance (X
(X
impedance printed transmission lines instead of lumped
inductors. The equations above provide good starting
values, though the values may need to be optimized to
account for layout and component parasitics.
50Ω
R
S
L
). Small inductance values may be realized using high-
Figure 5. Small Signal Circuit for the Input Port
C1
X
X
EXT
EXT
L1
L2
/2
/2
3
4
INT
) from the total reactance
X
X
INT
INT
/2
/2
28.1Ω
R
L
LT5560
5560 F05
5560f