lt5579 Linear Technology Corporation, lt5579 Datasheet - Page 15

• Manufacturer Part Number: lt5579
• Description: 1.5ghz To 3.8ghz High Linearity Upconverting Mixer
• Manufacturer: Linear Technology Corporation

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 LT5579 performs best at frequencies above
1500MHz, the part can be used down to 900MHz. The
internal RF transformer is not optimized for these lower
frequencies, thus the gain and impedance matching band-
width will decrease due to the low transformer inductance.
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 approximate matching band-
widths are listed in Table 5.
DC and RF Grounding
The LT5579 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 the board.
Several vias should connect the topside ground to other
ground layers to aid in thermal dissipation.
APPLICATIONS INFORMATION
LT5579
8
Figure 6. RF Output Circuit
9
10
V
11
CC
15
5579 F06
C8
L3
50Ω
RF
Table 4. Single-Ended RF Output Impedance
(at Pin 15, No External Matching)
Table 5. RF Output Component Values
*10dB Return Loss bandwidth
FREQUENCY
FREQUENCY
(MHz)
1650
1750
1950
2140
2600
3600
(MHz)
Figure 7. RF Output Return Loss with 1750MHz (a),
2140MHz (b), 2600MHz (c) and 3600MHz (d) Matching
1250
1750
1950
2150
2300
2600
3600
–20
–10
–15
–25
–5
0
1500
C8 (pF)
0.45
0.45
1.5
1.2
0.7
IMPEDANCE
RF OUTPUT
1
11.0+j42.7
55.6+j83.4
73.7–j37.7
35.2–j21.5
21.9+j17.8
119+j62.4
116–j21.0
a
2000
b
FREQUENCY (MHz)
2500
L3 (nH)
c
6.8
6.8
4.7
3.9
1.8
0Ω
3000
REFLECTION COEFFICIENT
MAG
0.78
0.62
0.52
0.42
0.34
0.30
0.45
MATCH BW (at 12dB RL)
3500
2260 to 2780*
3170 to 4100*
5579 F07
1630 to 1770
1725 to 1870
1840 to 2020
2035 to 2285
d
4000
LT5579
ANGLE
–10.4
–40.9
–110
97.4
47.8
21.9
134
15
5579f