LTC5505 LINER [Linear Technology], LTC5505 Datasheet - Page 12

• Manufacturer Part Number: LTC5505
• Description: 800MHz to 2.7GHz High Linearity Direct Conversion Quadrature Demodulator
• Manufacturer: LINER [Linear Technology]

LT5575
APPLICATIONS INFORMATION
The RF input impedance and S11 parameters (without
external matching components) are listed in Table 1.
Table 1. RF Input Impedance
LO Input Port
The demodulator’s LO input interface is shown in Fig-
ure 6. The input consists of an integrated transformer and a
precision quadrature phase shifter which generates 0° and
90° phase-shifted LO signals for the LO buffer amplifi ers
driving the I/Q mixers. The primary side of the transformer
is connected to the LO input pin. The secondary side of
the transformer is connected to the differential inputs of
the LO quadrature generator. Under no circumstances
should an external DC voltage be applied to the input pin.
DC current fl owing into the primary side of the transformer
may damage the transformer. A series blocking capacitor
should be used to AC-couple the LO input port to the LO
signal source.
12
FREQUENCY
(GHz)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
IMPEDANCE (
25.2 +j 35.5
10.5 +j 24.9
13.8 +j 28.8
18.6 +j 32.5
33.6 +j 36.8
43.1 +j 34.6
51.4 +j 28.4
55.8 +j 19.3
55.4 +j 10.4
42.3 +j –0.8
38.4 +j –0.3
29.7 +j 11.1
51.8 +j 3.9
46.9 +j 0.4
31.5 +j 4.9
29.9 +j 9.1
8.1 +j 21.3
35.4 +j 1
33 +j 2.9
30.4 +j 7
INPUT
Ω
)
0.760
0.715
0.660
0.595
0.521
0.441
0.355
0.270
0.188
0.110
0.042
0.032
0.084
0.131
0.172
0.207
0.235
0.258
0.274
0.287
MAG
S11
ANGLE (°)
–173.9
–178.2
133.0
125.4
117.2
108.6
172.7
175.3
168.4
161.9
155.4
149.2
143.4
99.6
90.3
80.8
71.6
56.9
63
63
The LO input port is internally matched over a wide fre-
quency range from 1.5GHz to 2.7GHz with input return
loss typically better than 10dB. No external matching
network is needed for this frequency range. When the part
is operated at a lower frequency, the input return loss can
be improved with the matching network shown in Figure
6. Shunt capacitor C12 and series capacitor C13 can be
selected for optimum input impedance matching at the
desired frequency as illustrated in Figure 7. For lower
frequency operation, external matching component C13
can serve as the series DC blocking capacitor.
INPUT
LO
Figure 7. LO Input Return Loss with External Matching
C13
LOW BAND AND
NETWORK FOR
MATCHING
EXTERNAL
MID BAND
–10
–15
–20
–25
–30
–5
0
C12
0.5
Figure 6. LO Input Interface
1.0
11
10
LO
FREQUENCY (GHz)
C13 = 5.6pF;
C12 = 3.9pF
1.5
C13 = 5.6pF;
NO SHUNT CAP
2.0
NO EXTERNAL
MATCHING
2.5
BUFFER AMPLIFIERS
LO QUADRATURE
GENERATOR AND
5575 F07
3.0
5575 F06
5575f