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LT5579IUH#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
LT5579
13
5579fa
applicaTions inForMaTion
C9 to step the impedance up to about 12.5Ω. At lower
frequencies additional series inductance may be required
between the IF ports and C9. The position of C9 may vary
with the IF frequency due to the different series inductance
requirements. The 4:1 impedance ratio of transformer T1
completes the transformation to 50 ohms. Table 1 lists the
differential IF input impedances and reflection coefficients
for several frequencies.
Table 1. IF Input Differential Impedance
FREQUENCY
(MHz)
IF INPUT
IMPEDANCE
REFLECTION COEFFICIENT
MAG ANGLE
70 8.8+j1.3 0.70 177
140 8.7+j2.3 0.70 175
170 9.0+j2.8 0.70 174
190 8.9+j3.0 0.70 173
240 9.0+j4.0 0.70 170
380 9.7+j4.9 0.68 168
450 10.0+j5.2 0.67 167
750 10.8+j9.4 0.65 158
1000 11.8+j13.8 0.64 148
The purpose of capacitor C3 is to improve the LO-RF
leakage in some applications. This relatively small-valued
capacitor has little effect on the impedance match in most
cases. This capacitor should typically be located close to
the IC, however, there may be cases where re-positioning
the capacitor may improve performance.
The measured return loss of the IF input is shown in
Figure 3 for application frequencies of 70MHz, 240MHz
and 456MHz. Component values are listed in Table 2. (For
70MHz matching details, refer to Figure 8.)
Table 2. IF Input Component Values
FREQUENCY
(MHz)
C1, C2
(pF)
C9
(pF)
C3
(pF)
L1, L2
(nH)
R1, R2
(Ω)
MATCH BW
(at 12dB RL)
70(3) 1000 120 (1) 100 9.1 <50
to 158
140 180 22 (1) 100 9.1 112
to 170
240 82 33 (1) 40 11 174
to 263
450 33 33 (1) 40 11 330
to 505
Note: (1) Depends on RF, (2) T1 = M/A-Com MABAES0061,
(3)
See Figure 8
FREQUENCY (MHz)
0
RETURN LOSS (dB)
–10
–5
0
300 500 800
5579 F03
–15
–20
–25
100 200
a
b
c
400
600 700
Figure 3. IF Input Return Loss with 70MHz (a),
240MHz (b) and 456MHz (c) Matching
LT5579
14
5579fa
applicaTions inForMaTion
LO Input Interface
The simplified schematic for the single-ended LO input port
is shown in Figure 4. An internal transformer provides a
broadband impedance match and performs single-ended
to differential conversion. An internal capacitor also aids
in impedance matching and provides DC isolation to the
primary transformer winding. The transformer secondary
feeds the differential limiting amplifier stages that drive
the mixer core.
The measured return loss of the LO input port is shown
in Figure 5 for an LO input power of –1dBm. The imped
-
ance match
is acceptable from about 1.1GHz to beyond
4GHz, with a minimum return loss across this range of
about 9dB at 2300MHz. If desired, the return loss can
be improved below 1.1GHz by external components as
shown in Figure 4. The return loss can also be improved
by reducing the LO drive level, though performance will
degrade if the level is too low.
While external matching of the LO input is not required
for frequencies above 1.1GHz, external matching should
be used for lower LO frequencies for best performance.
Table 3 lists the input impedance and reflection coefficient
vs frequency for the LO input for use in such cases.
Table 3. Single-Ended LO Input Impedance
(at Pin 22, No External Match)
FREQUENCY
(MHz)
INPUT
IMPEDANCE
REFLECTION COEFFICIENT
MAG ANGLE
750 63.3||– j30.5
0.68 –125
1000 20.3||– j1120
0.42 –179
1500 78.4||– j1250
0.22 –7.7
1900 79.1||– j113
0.34 –65.2
2000 74.7||– j96.3
0.35 –74.7
2150 66.8||– j81.5
0.36 –87.0
2400 53.8||– j69.8
0.35 –105
3050 33.7||– j115
0.26 –148
3150 33.0||– j146
0.24 –154
4000 43.9||+ j173
0.15 123
V
BIAS
V
CC
LO
C13
5579 F04
L6
LO
INPUT
EXTERNAL
MATCHING
FOR LOW
FREQUENCY
ONLY
22
Figure 4. LO Input Circuit
FREQUENCY (MHz)
500 1000
–25
RETURN LOSS (dB)
–15
0
1500
2500
3000
5579 F05
–20
–5
–10
2000
3500
4000
Figure 5. LO Input Return Loss
LT5579
15
5579fa
15
118 109
V
CC
C8
5579 F06
LT5579
L3
RF
50Ω
Figure 6. RF Output Circuit
FREQUENCY (MHz)
1500
RETURN LOSS (dB)
–10
–5
0
3500
5579 F07
–15
–20
–25
a b
c
d
2000
2500
3000
4000
Figure 7. RF Output Return Loss with 1750MHz (a),
2140MHz (b), 2600MHz (c) and 3600MHz (d) Matching
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 L
T5579 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.
Table 4. Single-Ended RF Output Impedance
(at Pin 15, No External Matching)
FREQUENCY
(MHz)
RF OUTPUT
IMPEDANCE
REFLECTION COEFFICIENT
MAG ANGLE
1250 11.0+j42.7 0.78 97.4
1750 55.6+j83.4 0.62 47.8
1950 119+j62.4 0.52 21.9
2150 116–j21.0 0.42 –10.4
2300 73.7–j37.7 0.34 –40.9
2600 35.2–j21.5 0.30 –110
3600 21.9+j17.8 0.45 134
Table 5. RF Output Component Values
FREQUENCY
(MHz)
C8 (pF)
L3 (nH)
MATCH BW (at 12dB RL)
1650 1.5 6.8 1630
to 1770
1750 1.2 6.8 1725
to 1870
1950 1 4.7 1840
to 2020
2140 0.45 3.9 2035
to 2285
2600 – 1 2260
to 2780*
3600 0.7 0Ω 3170
to 4100*
*10dB Return Loss bandwidth
applicaTions inForMaTion
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

LT5579IUH#TRPBF

Mfr. #:
Buy LT5579IUH#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
RF Mixer 1.5 GHz to 3.8GHz High Linearity Upconverting Mixer
Lifecycle:
New from this manufacturer.
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