13
LT5526
5526f
APPLICATIO S I FOR ATIO
WUUU
Figure 12. Typical Return Loss Performance with
a 240MHz Narrowband Bridge IF Balun (Swept IF)
Figure 13. Typical Gain and IIP3 Performance with
a 240MHz Narrowband Bridge IF Balun (Swept IF)
IF
+
C12
IF
OUT
50Ω
L12
L11
C11
IF
–
V
CC
C13
C14
L14
OPT
L13
OPT
5526 F11
Figure 11. Narrowband Bridge IF Balun
LL
RR
CC
RR
IF L
IF L
11 12
11 12
1
==
==
•
•
ω
ω
I
nductors L13 and L14 provide a DC path between V
CC
and the IF
+
pin. Only one of these inductors is required.
Low cost multilayer chip inductors are adequate for L11,
L12 and L13. If L14 is used instead of L13, a larger value
is usually required, which may require the use of a wire-
wound inductor. Capacitor C13 is a DC block which can
also be used to adjust the impedance match. Capacitor
C14 is a bypass capacitor.
Typical return loss of the IF output port is plotted versus
frequency in Figure 12 for a 240MHz balun design. For this
example, L11 = L12 = 100nH, C11 = C12 = 3.9pF, L14 =
560nH and C13 = 100pF. Performance versus IF output
frequency is shown in Figure 13 in the case of a 1900MHz
RF input. These results show that the usable IF bandwidth
is greater than 60MHz, assuming tight tolerance matching
components. Contact the factory for applications assis-
tance with this circuit.
FREQUENCY (MHz)
100
–25
RETURN LOSS (dB)
–20
–15
–10
–5
0
150
200 250 300
5526 F12
350 400
IF FREQUENCY (MHz)
190
GAIN (dB), IIP3 (dBm)
10
15
20
270
5526 F13
5
0
–5
210
IIP3
GAIN
230
250
290
T
A
= 25°C
f
RF
= 1900MHz
f
LO
= f
RF
– f
IF
P
LO
= –5dBm
