LT5560
15
5560f
APPLICATIO S I FOR ATIO
WUU
U
The LT5560 consists of a double-balanced mixer, a com-
mon-base input buffer amplifi er, and bias/enable circuits.
The IC has been designed for frequency conversion applica-
tions up to 4GHz, though operation over a wider frequency
range may be possible with reduced performance. For best
performance, the input and output should be connected
differentially. The LO input can be driven by a single-ended
source with either low side or high side LO operation. The
LT5560 is characterized and production tested using a
single-ended LO drive.
The quiescent DC current of the LT5560 can be adjusted
from less than 4mA to approximately 13.5mA through
the use of an external resistor. This functionality gives the
user the ability to make application dependent trade-offs
between IIP3 performance and DC current.
Three demo boards, as described in Table 1, are available
depending on the desired application. The listed input
and output frequency ranges are based on measured
12dB return loss bandwidths and the LO port frequency
ranges are based on 10dB return loss bandwidths. The
general circuit topologies are shown in Figures 1, 2 and
3 for DC963B, DC991A and DC1027A, respectively. The
board layouts are shown in Figures 23, 24 and 25. The
low frequency board, DC1027A, can be reconfi gured for
upconverting applications.
Figure 4. Input Port with Lowpass
External Matching Topology
provided through the center-tap of an input transformer,
as shown, or through matching inductors or chokes con-
nected from pins 3 and 4 to ground.
IN
+
IN
–
INPUT
LT5560
C1
R1
L1
L2
T1
V
BIAS
3
4
5560 F04
Signal Input Port
Figure 4 shows a simplifi ed schematic of the differential
input signal port and an example topology for the external
impedance matching circuit. Pins 3 and 4 each source
up to 6mA of DC current. This current can be reduced by
the addition of resistor R1 (adjustable mixer current is
discussed in a later section). The DC ground path can be
Table 1. LT5560 Demo Board Descriptions
MIXER
DESCRIPTION
DEMO
BOARD
NUMBER
INPUT
FREQ.
(MHz)
OUTPUT
FREQ.
(MHz)
LO
FREQ.
(MHz)
Upconverting,
Cellular Band
DC963B 50-190 850-940 530-930
Downconverting
Cellular Band
DC991A 710-1300 110-170 530-930
Downconverting,
VHF Band
DC1027A 115-295 3-60 180-310
Note: Consult factory for demo boards for UMTS, WLAN and other bands.
The lowpass impedance matching topology shown may
be used to transform the differential input impedance
at pins 3 and 4 to match that of the signal source. The
differential input impedances for several frequencies are
listed in Table 2.
Table 2. Input Signal Port Differential Impedance
FREQUENCY
(MHz)
INPUT
IMPEDANCE
(Ω)
REFLECTION COEFFICIENT (Z
O
= 50Ω)
MAG ANGLE (DEG.)
70 28.5 + j0.8 0.274 177
140 28.5 + j1.6 0.274 174
240 28.6 + j2.7 0.275 171
360 28.6 + j4.0 0.276 167
450 28.6 + j4.9 0.278 163
750 28.8 + j8.2 0.287 153
900 28.8 + j9.8 0.294 148
1500 29.1 + j16.3 0.328 138
1900 29.4 + j20.8 0.357 120
2150 29.6 + j23.6 0.376 114
2450 29.9 + j27.0 0.399 107
3600 31.7 + j42.1 0.499 86.2
