LT5527 LINER [Linear Technology], LT5527 Datasheet - Page 13

• Manufacturer Part Number: LT5527
• Description: 400MHz to 3.7GHz 5V High Signal Level Downconverting Mixer
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Compared to the lowpass/4:1 transformer matching tech-
nique, this network delivers approximately 0.8dB higher
conversion gain (since the IF transformer loss is elimi-
nated) and comparable noise fi gure and IIP3. At a ±15%
offset from the IF center frequency, conversion gain and
noise fi gure degrade about 1dB. Beyond ±15%, conver-
sion gain decreases gradually but noise fi gure increases
rapidly. IIP3 is less sensitive to bandwidth. Other than IF
bandwidth, the most signifi cant difference is LO-IF leakage,
which degrades to approximately –38dBm compared to
the superior performance realized with the lowpass/4:1
transformer matching.
Discrete IF balun element values for four common IF fre-
quencies are listed in Table 5. The corresponding measured
IF output return losses are shown in Figure 11. The values
listed in Table 5 differ from the calculated values slightly
due to circuit board and component parasitics. Typical
conversion gain, IIP3 and LO-IF leakage, versus RF input
frequency, for all four IF frequency examples is shown in
Figure 12. Typical conversion gain, IIP3 and noise fi gure
versus IF output frequency for the same circuits are shown
in Figure 13.
Table 5. Discrete IF Balun Element Values (R
For fully differential IF architectures, the IF transformer can
be eliminated. An example is shown in Figure 14, where
the mixer’s IF output is matched directly into a SAW fi lter.
Supply voltage to the mixer’s IF pins is applied through
L L
L
C C
IF FREQUENCY
1 2
3
6 7
,
,
=
(MHz)
190
240
380
450
ω
X
=
=
IF
IF
ω
R
IF
IF
ω
•
•
IF
R
R
OUT
1
IF
L1, L2
(nH)
•
120
100
56
47
R
OUT
C6, C7
(pF)
6.8
4.7
2.7
3
OUT
= 50Ω)
(nH)
220
220
L3
68
47
Figure 11. IF Output Return Losses with Discrete Balun Matching
Figure 12. Conversion Gain, IIP3 and LO-IF Leakage vs RF Input
Frequency Using Discrete IF Balun Matching
Figure 13. Conversion Gain, IIP3 and SSB NF vs IF Output
Frequency Using Discrete IF Balun Matching
–10
–15
–20
–25
–30
–5
26
24
22
20
18
16
14
12
10
26
24
22
20
18
16
14
12
10
0
8
6
4
2
8
6
4
2
0
1700
150
50
IIP3
SSB NF
G
IIP3
G
C
100
C
190MHz
200
1900
150
IF OUTPUT FREQUENCY (MHz)
190IF
240IF
380IF
450IF
240MHz
RF INPUT FREQUENCY (MHz)
250
200
IF FREQUENCY (MHz)
300
2100
250
300
350
380MHz
LOW SIDE LO (–3dBm)
T
LOW SIDE LO (–3dBm)
T
A
A
= 25°C
2300
= 25°C
350
400
400
450
450MHz
2500
450
500
LO-IF
190IF
240IF
380IF
450IF
500
5527 F11
5527 F12
5527 F13
2700
550
550
LT5527
–50
0
–10
–20
–30
–40
–60
13
5527fa