LT5575
13
5575f
APPLICATIONS INFORMATION
The LO input impedance and S11 parameters (without
external matching components) are listed in Table 2.
Table 2. LO Input Impedance
FREQUENCY
(GHz)
INPUT
IMPEDANCE (
Ω)
S11
MAG ANGLE (°)
0.8 9.6 +j 23.7 0.731 127.9
0.9 13 +j 27.1 0.669 120.4
1.0 17.9 +j 30 0.592 113.2
1.1 24.1 +j 31.7 0.508 106.1
1.2 31.2 +j 31.4 0.421 99.8
1.3 37.5 +j 28.9 0.341 95.1
1.4 41.9 +j 24.6 0.272 93.4
1.5 43.4 +j 20 0.221 96.2
1.6 42.9 +j 16.4 0.189 103.5
1.7 41.2 +j 14.1 0.18 113.1
1.8 39.5 +j 13.1 0.186 120.3
1.9 37.8 +j 13.1 0.201 124.5
2.0 36.6 +j 13.6 0.217 125.6
2.1 35.6 +j 14.6 0.236 125
2.2 35.1 +j 15.7 0.25 123.1
2.3 34.9 +j 17.1 0.264 120.1
2.4 35.1 +j 18.5 0.272 116.6
2.5 35.5 +j 19.9 0.281 113
2.6 36.3 +j 21.2 0.284 109
2.7 37.2 +j 22.5 0.287 105.1
I-Channel and Q-Channel Outputs
Each of the I-channel and Q-channel outputs is internally
connected to V
CC
through a 65Ω resistor. The output DC
bias voltage is V
CC
– 1.1V. The outputs can be DC-coupled
or AC-coupled to the external loads. Each single-ended
output has an impedance of 65Ω in parallel with a 5pF
internal capacitor, forming a low-pass fi lter with a –3dB
corner frequency at 490MHz. The loading resistance
on each output, R
LOAD
(single-ended), should be larger
than 300Ω to assure full gain. The gain is reduced by
20 • log
10
(1 + 65Ω/R
LOAD
) in dB when the output port is
terminated by R
LOAD
. For instance, the gain is reduced
by 7.23dB when each output pin is connected to a
50Ω load (or 100Ω differentially). The output should be
taken differentially (or by using differential-to-single-
ended conversion) for best RF performance, including
NF and IM2.
The phase relationship between the I-channel output signal
and the Q-channel output signal is fi xed. When the LO
input frequency is larger (or smaller) than the RF input
frequency, the Q-channel outputs (Q
OUT
+
, Q
OUT
–
) lead (or
lag) the I-channel outputs (I
OUT
+
, I
OUT
–
) by 90°.
When AC output coupling is used, the resulting high-
pass fi lter’s –3dB roll-off frequency is defi ned by the RC
constant of the blocking capacitor and R
LOAD
, assuming
R
LOAD
>> 65Ω.
Figure 8. I/Q Output Equivalent Circuit
15
16
V
CC
I
OUT
+
I
OUT
–
5575 F08
13
14
Q
OUT
+
Q
OUT
–
65Ω 5pF65Ω65Ω65Ω 5pF5pF5pF
