LTC5593
21
5593f
Figure 4. Channel-to-Channel Isolation vs C8 Values
RF FREQUENCY (GHz)
2.2
30
40
45
50
2.4
2.6
2.7
5593 F04
35
2.3 2.5
2.8
C8 OPEN
C8 = 2.2pF
C8 = 10pF
channel-to-channel isolation at specific RF operation
frequency with minor impact to conversion gain, linearity
and noise performance. The channel-to-channel isola-
tion performance with different values of C8A is given in
Figure 4. When used, it should be located within 2mm of
Pin 2 for proper high frequency decoupling. The nominal
DC voltage on the CTA pin is 1.2V.
APPLICATIONS INFORMATION
Figure 6. LO Input Schematic
The RF input impedance and input reflection coefficient,
versus RF frequency, are listed in Table 1. The reference
plane for this data is Pin 1 of the IC, with no external
matching, and the LO is driven at 2.31GHz.
Table 1. RF Input Impedance and S11
(at Pin1, No External Matching, LO Input Driven at 2.31GHz)
FREQUENCY
(GHZ)
RF INPUT
IMPEDANCE
S11
MAG ANGLE
2.0 74.2 + j13.6 0.22 23.1
2.2 69.4 – j6.4 0.17 –15.2
2.4 45.2 – j3.0 0.06 –146.0
2.6 45.6 + j6.5 0.08 120.3
2.8 48.3 + j10.9 0.11 92.3
3.0 51.5 + j14.1 0.14 75.9
3.2 57.1 + j15.5 0.16 57.3
3.4 62.6 + j11.8 0.15 37.2
3.6 64.3 + j4.7 0.13 16.0
3.8 63.6 – j6.8 0.13 –23.2
4.0 50.8 – j10.7 0.11 –79.4
LO Input
The LO input, shown in Figure 6, is connected to the pri-
mary winding of an integrated transformer. A 50Ω imped-
ance match from 2.1GHz to 3.4GHz is realized at the LO
port by adding a 1.5pF external series capacitor, C2. This
capacitor is also needed for DC blocking if the LO source
has DC voltage present, since the primary side of the LO
transformer is DC-grounded internally. The DC resistance
of the primary is approximately 1.8Ω. For LO frequency
Figure 5. RF Port Return Loss
RF FREQUENCY (GHz)
2.0
30
15
20
10
5
2.4
3.0
3.2 3.4 3.6 3.82.8
5593 F05
25
2.2 2.6
4.0
LO = 2.4GHz
LO = 3GHz
LO = 3.6GHz
LO
L4
TO
MIXER B
LTC5593
I
SEL
5593 F06
18
LO
16
17
ENA
ENB
C2
14
BIAS
BIAS
TO
MIXER A
For the RF inputs to be properly matched, the appropriate
LO signal must be applied to the LO input. A broadband
input match is realized with C1A = 22pF. The measured
input return loss is shown in Figure 5 for LO frequencies
of 2.4GHz, 3.0GHz and 3.6GHz. These LO frequencies
correspond to lower, middle and upper values in the LO
range. As shown in Figure 5, the RF input impedance is
dependent on LO frequency, although a single value of
C1A is adequate to cover the 2.3GHz to 4.0GHz RF band.
