LTC5549
15
5549fa
For more information www.linear.com/LTC5549
applicaTions inForMaTion
Figure 5. Simplified LO Input Schematic
Figure 6. LO Input Return Loss
limiting differential amplifier and an LO frequency doubler.
The LTC5549’s LO amplifier is optimized for the 1GHz
to 12GHz LO frequency range. LO frequencies above or
below this frequency range may be used with degraded
performance. The LO frequency doubler is controlled by
a digital voltage input at X2 (Pin 8). When the X2 voltage
is higher than 1.2V, the LO frequency doubler is enabled.
When X2 is left open or its voltage is lower than 0.5V, the
LO frequency doubler is disabled.
The mixer’s LO input is connected to a singled-ended to
differential buffer and ESD devices. The DC voltage at the
LO input is about 1.6V. A DC blocking capacitor is required
for the LO circuit to operate properly.
The LO is 50Ω matched from 1GHz to 12GHz. With a
0.15pF shunt capacitor (C4) located 3.55mm away from
the LO pin. The LO port is 50Ω matched from 1GHz to
8.4GHz without C4. External matching components may
be needed for extended LO operating frequency range.
The measured LO input return loss is shown in Figure 6.
The nominal LO input level is 0dBm, although the limiting
amplifiers will deliver
excellent performance over a ±6dBm
input power range.
IF Port
The mixer’s IF port, shown in Figure 7, is connected to the
primary winding of an integrated transformer. The primary
side of the IF transformer is DC-grounded internally and
the DC resistance is approximately 6.2Ω. A DC blocking
capacitor is needed if the IF source has DC voltage present.
The secondary winding of the IF transformer is internally
connected to the mixer core.
Figure 7. Simplified IF Port Interface Schematic
The IF port is broadband matched to 50Ω from 500MHz to
6GHz. An LO signal between -6dBm and 6dBm is required
for good IF impedance matching. Frequencies outside of
this range can be used with degraded performance.
The measured IF port return loss is shown in Figure 8.
LTC5549
LO
X2 V
CC
5549 F05
X2
8 9
11
LO
IN
C5
C4
LTC5549
IF
IF
5549 F07
2
Figure 8. IF Port Return Loss
LO FREQUENCY (GHz)
1 13
5549 F06
20
30
2 3 4 5 6 7 8 9 10 11 12
0
15
10
5
25
RETURN LOSS (dB)
X2 = LOW, EN = HIGH
X2 = LOW, EN = LOW
X2 = HIGH, EN = HIGH
IF FREQUENCY (GHz)
0.5 6
5549 F08
30
40
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
0
25
20
15
10
5
35
RETURN LOSS (dB)
