lt5521 Linear Technology Corporation, lt5521 Datasheet - Page 13

• Manufacturer Part Number: lt5521
• Description: Very High Linearity Active Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Table 6. Matching Values Using M/A-COM ETC1.6-4-2-3
Output Transformer
For applications with LO and output frequencies below
1GHz, the M/A-COM MABAES0054 is recommended for
the output component T2. This transformer maintains
better low frequency output symmetry. Table 7 lists com-
ponents necessary for a 750MHz output match using the
M/A-COM MABAES0054.
Table 7. Matching Values Using M/A-COM MABAES0054
Output Transformer
Hybrid baluns provide a low cost alternative for differen-
tial to single-ended conversion. The critical performance
parameters of conversion gain, IIP3, noise figure and LO
suppression are largely unaffected by these transform-
ers. However, their limited bandwidth and reduced sym-
metry outside the frequency of operation degrades the
suppression of higher order LO harmonics, particularly
2xLO. Murata LBD21 series hybrid balun transformers,
for example, can be used for output frequencies as low as
840MHz and as high as 2.4GHz.
750MHz
2.4GHz
2.2GHz
2.0GHz
1.7GHz
1.3GHz
1.0GHz
f
f
OUT
OUT
Figure 10. Output Return Loss vs Frequency
–10
–20
–25
–30
–15
–5
5
0
0.7
L1, L2
L1, L2
2.7nH
4.7nH
10nH
10nH
33nH
0nH
1nH
U
2GHz
1.2
FREQUENCY (GHz)
U
3.9pF
82pF
82pF
82pF
82pF
82pF
82pF
C3
C3
1.7
1GHz
W
82pF
82pF
82pF
82pF
82pF
C12
C12
1nF
1nF
2.2
5521 F10
f (10dB RL)
f (10dB RL)
U
450MHz
430MHz
400MHz
400MHz
400MHz
500MHz
500MHz
Johanson Technology supplies the 3700BL15B100S hy-
brid balun for use between 3.4GHz and 4GHz. With addi-
tional matching, this transformer can be used for
applications between 3.3GHz and 3.7GHz. Example LT5521
performance is shown in Figure 11.
LO Interface
The LO input pin is internally matched to 50 . It has an
internal DC bias of 960mV. External AC coupling is re-
quired. Figure 12 shows a simplified schematic of the LO
input. Overdriving the LO input will dramatically reduce
the performance of the mixer. The LO input power should
not exceed +1dBm for normal operation. Select C1 (Figure
12) only large enough to achieve the desired LO input
return loss. This reduces external low frequency signal
amplification through the LO buffer.
For applications with LO frequency in the range of 2.1GHz
to 2.4GHz, the LT5521 achieves improved distortion and
Figure 11. LT5521 Performance for an Application Tuned to
3.5GHz with Low Side (LS) and High Side (HS) LO Injection
LO
50
IN
10
–2
–4
8
6
4
2
0
Figure 12. Simplified LO Input Circuit
3.2
C1
T
f
IF
A
= 300MHz
= 25 C
3.3
15
G
LT5521
C
V
CC
3.4
FREQUENCY (GHz)
8
3.5
HS
HS
LS
LS
3.6
HS
60
60
LS
5521 F12
3.7
IIP3
NF
5521 F11
3.8
22
20
18
16
14
12
10
8
LT5521
13
5521f