LT5527
13
5527fa
APPLICATIONS INFORMATION
LL
RR
CC
RR
L
X
IF OUT
IF
IF IF OUT
IF
IF
12
67
1
3
,
•
,
••
=
=
=
ω
ω
ω
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
OUT
= 50Ω)
IF FREQUENCY
(MHz)
L1, L2
(nH)
C6, C7
(pF)
L3
(nH)
190 120 6.8 220
240 100 4.7 220
380 56 3 68
450 47 2.7 47
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
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
IF FREQUENCY (MHz)
–30
IF PORT RETURN LOSS (dB)
–20
–10
0
–25
–15
–5
150 250 350 450
5527 F11
55010050 200 300 400 500
190MHz
240MHz 380MHz
450MHz
RF INPUT FREQUENCY (MHz)
1700
G
C
(dB), IIP3 (dBm)
LO-IF LEAKAGE (dBm)
14
18
22
26
2500
5527 F12
10
6
12
16
20
24
8
4
2
–30
–20
–10
0
–40
–50
–60
1900
2100
2300
2700
190IF
240IF
380IF
450IF
LOW SIDE LO (–3dBm)
T
A
= 25°C
IIP3
LO-IF
G
C
IF OUTPUT FREQUENCY (MHz)
150
G
C
, SSB NF (dB), IIP3 (dBm)
12
18
20
550
5527 F13
10
8
0
250
350
450
200
300
400
500
4
26
24
22
IIP3
G
C
16
14
6
2
190IF
240IF
380IF
450IF
LOW SIDE LO (–3dBm)
T
A
= 25°C
SSB NF
