lt5560 Linear Technology Corporation, lt5560 Datasheet - Page 24

• Manufacturer Part Number: lt5560
• Description: 0.01mhz To 4ghz Low Power Active Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5560
Measured IF
mixer with lumped element baluns are shown on page 1.
Additional performance parameters vs RF input frequency
are plotted in Figure 20.
Low Frequency Applications
At low IF frequencies, where transformers can be impracti-
cal due to their large size and cost, alternate methods can
be used to achieve desired differential to single-ended
conversions. The examples in Figures 21 and 22 use an
24
200MHz
RF
IN
Figure 20. Performance of 900MHz Downconverting
Mixer with Lumped Element Baluns
WBC4-6TL
1:1
T1
13
11
10
12
OUT
9
8
7
6
4
5
800
and IM3 levels vs RF input power for the
3Ω
R1
U
850
INPUT FREQUENCY (MHz)
200.45MHz
15pF
SSB NF
C1
GAIN
IIP3
LO
V
EN
IN
U
Figure 21. A 200MHz to 450KHz Downconverter with Active IF Interface
12nH
12nH
900
L1
L2
10nF
160Ω
C3
1
2
3
4
W
R2
950
LO
EN
IN
IN
+
–
–
5560 F20
1000
LT5560
PGND
9
U1
U
OUT
OUT
LO
V
CC
+
+
–
10nF
C5
8
7
6
5
op-amp to demonstrate performance with an output fre-
quency of 450KHz. Pull-up resistors R3 and R4 are used
at the open-collector IF outputs instead of large inductors.
The op-amp provides gain and converts the mixer dif-
ferential outputs to single-ended. At low frequencies, the
LO port can be easily matched with a shunt resistor and
a DC blocking cap. This IF interface circuit can be used
for signals up to 1MHz.
Figure 21 shows an input match that uses a transformer
to present a differential signal to the mixer. A possible
alternative, shown in Figure 22, is to use a single-ended
drive on one input pin, with the other pin grounded. This
approach is more cost effective than the transformer,
however, some performance is sacrifi ced. Another option
is to use a lumped-element balun, which requires only one
more component than the single-ended impedance match,
but could provide better performance. Measured data for
the examples below are summarized in Table 8.
Table 8. Low-Frequency Performance
(MHz)
200
90
f
IN
200Ω
R3
(MHz)
200Ω
f
0.45
0.45
R4
OUT
C12
1µF
C11
1µF
1nF
C6
(dB)
6.8
G
9
C
200Ω
R5
+
–
LT6202
200Ω
R6
U2
(dBm)
IIP3
3.8
3.3
C13
1µF
DSB NF
11.6
(dB)
5.1kΩ
5.1kΩ
22
R8
R9
C14
1µF
51Ω
R7
(mA)
1µF
C8
450kHz
I
14
18
IF
CC
OUT
5560f
5V