LTC5593
22
5593f
Figure 7. LO Input Return Loss
APPLICATIONS INFORMATION
from 3.4GHz to 3.8GHz, the LO port can be well matched
by using C2 = 0.6pF and L4 = 10nH.
The secondary of the transformer drives a pair of high
speed limiting differential amplifiers for channels A and B.
The LTC5593’s LO amplifiers are optimized for the 2.1GHz
to 4.2GHz LO frequency range; however, LO frequencies
outside this frequency range may be used with degraded
performance.
The LO port is always 50Ω matched, even when one or
both of the channels is disabled. This helps to reduce fre-
quency pulling of the LO source when the mixer is switched
between different operating states. Figure 7 illustrates the
LO port return loss for the different operating modes.
The nominal LO input level is 0dBm, though the limiting
amplifiers will deliver excellent performance over a ±6dBm
input power range. Table 2 lists the LO input impedance
and input reflection coefficient versus frequency.
Table 2. LO Input Impedance vs Frequency
(at Pin 16, No External Matching, ENA = ENB = High)
FREQUENCY
(GHz)
INPUT
IMPEDANCE
S11
MAG ANGLE
2.0 33.8 + j22.8 0.32 110.3
2.2 34.8 + j22.2 0.31 109.7
2.4 34.5 + j21.8 0.31 110.9
2.6 32.5 + j22.8 0.34 111.9
2.8 30.7 + j25.9 0.38 108.8
3.0 29.6 + j30.1 0.43 103.4
3.2 29.3 + j34.8 0.47 97.1
3.4 29.3 + j38.7 0.50 92.1
3.6 30.7 + j43.1 0.52 86.0
3.8 33.0 + j46.9 0.52 80.5
4.0 36.1 + j49.8 0.52 75.6
LO FREQUENCY (GHz)
2.0
35
30
20
15
10
2.2
3.0
3.4
5593 F07
25
5
2.8
3.8
4.0
2.4
2.6
3.2 3.6
BOTH CHANNELS ON
ONE CHANNEL ON
BOTH CHANNELS OFF
C2 = 1.5pF
L4 = OPEN
C2 = 0.6pF
L4 = 10nH
IF Outputs
The IF amplifiers in channels A and B are identical. The IF
amplifier for channel A, shown in Figure 8, has differen-
tial open collector outputs (IFA
+
and IFA
–
), a DC ground
return pin (IFGNDA), and a pin for adjusting the internal
bias (IFBA). The IF outputs must be biased at the sup-
ply voltage (V
CCIFA
), which is applied through matching
inductors L1A and L2A. Alternatively, the IF outputs can
be biased through the center tap of a transformer (T1A).
The common node of L1A and L2A can be connected to
the center tap of the transformer. Each IF output pin draws
approximately 50mA of DC supply current (100mA total).
An external load resistor, R2A, can be used to improve
impedance matching if desired.
IFGNDA (Pin 23) must be grounded or the amplifier will
not draw DC current. Inductor L3A may improve LO-IF
and RF-IF leakage performance in some applications, but
is otherwise not necessary. Inductors should have small
resistance for DC. High DC resistance in L3A will reduce
the IF amplifier supply current, which will degrade RF
performance.
