lt5578 MOSA electronics corp., lt5578 Datasheet - Page 12

• Manufacturer Part Number: lt5578
• Description: 0.4ghz To 2.7ghz High Linearity Upconverting Mixer
• Manufacturer: MOSA electronics corp.

APPLICATIONS INFORMATION
RF Output Interface
The RF output interface is shown in Figure 6. An internal
RF transformer reduces the mixer core output impedance
to simplify matching of the RF output pin. A center tap in
the transformer provides the DC connection to the mixer
core and the transformer provides DC isolation to the RF
output. The RF pin is internally grounded through the
secondary winding of the transformer, thus a DC voltage
should not be applied to this pin.
While the LT5578 performs best at frequencies above
700MHz, the part can be used down to 400MHz. The low
inductance of the internal transformer limits the perfor-
mance at lower frequencies. The impedance data for the RF
output, listed in Table 4, can be used to develop matching
networks for different frequencies or load impedances.
Figure 7 illustrates the output return loss performance
for several applications. The component values and ap-
proximate matching bandwidths are listed in Table 5.
DC and RF Grounding
The LT5578 relies on the back side ground for both RF
and thermal performance. The Exposed Pad must be
soldered to the low impedance topside ground plane of
LT5578
12
LT5578
8
9
Figure 6. RF Output Circuit
10
V
11
CC
15
5578 F06
C8
L3
C14
50Ω
RF
the board. As many vias as possible should connect the
topside ground to other ground layers to aid in thermal
dissipation and reduce inductance.
Table 4. Single-Ended RF Output Impedance
(at Pin 15, No External Matching)
Table 5. RF Output Component Values
FREQUENCY
Figure 7. RF Output Return Loss with 450MHz (a), 740MHz (b),
900MHz (c), 1950MHz (d) and 2600MHz (e) Matching
FREQUENCY
(MHz)
1950
2600
(MHz)
450
740
900
1200
1600
2000
2400
2800
400
800
–20
–25
–10
–15
–5
0
C8 (pF) L3 (nH) C14 (pF)
0
9.0
3.3
1.8
–
–
IMPEDANCE
RF OUTPUT
10.1 + j29.3
90.8 + j96.6
69.7 – j66.6
32.8 – j22.5
a
32.3 – j5.4
28.6 + j0.3
22.5 + j4.4
500
b
c
1000
0Ω
FREQUENCY (MHz)
1.8
18
18
12
1500
1.2
0.8
–
–
–
d
2000
REFLECTION COEFFICIENT
0.741
0.614
0.507
0.330
0.225
0.273
0.384
MAG
e
2500 3000
5578 F07
(at 12dB RL)
MATCH BW
1765-2305
2150-2990
430-505
680-768
835-970
ANGLE
–112.3
–159.3
117.6
–44.4
179.0
167.3
32.6
5578f