LTC5590IUH#TRPBF Linear Technology, LTC5590IUH#TRPBF Datasheet - Page 16

• Manufacturer Part Number: LTC5590IUH#TRPBF
• Manufacturer: Linear Technology

Specifications of LTC5590IUH#TRPBF

• Operating Supply Voltage: 3.3V
• Operating Temperature (min): -40C
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Compliant

Lowpass IF Matching
For IF frequencies below 90MHz, the inductance values
become unreasonably high and the lowpass topology
shown in Figure 9 is preferred. This topology also can
provide improved RF to IF and LO to IF isolation. V
is supplied through the center tap of the 4:1 transformer.
A lowpass impedance transformation is realized by shunt
elements R2A and C9A (in parallel with the internal RIF
and CIF), and series inductors L1A and L2A. Resistor
R2A is used to reduce the IF output resistance for greater
bandwidth, or it can be omitted for the highest conver-
sion gain. The final impedance transformation to 50Ω is
realized by transformer T1A. The measured return loss
is shown in Figure 11 for different values of inductance
(C9A = OpF). The case with 82nH inductors and R2A = 1k
is also shown. The LTC5590 demo board (see Figure 2)
LTC5590
applicaTions inForMaTion
Values of L1A and L2A are tabulated in Figure 1 for vari-
ous IF frequencies. The measured IF output return loss
for bandpass IF matching is plotted in Figure 9.
Table 3. IF Output Impedance vs Frequency
16
Figure 9. IF Output Return Loss with Bandpass Matching
FREQUENCY (MHz)
–10
–15
–20
–25
–5
0
50
140
190
240
300
380
450
90
270nH
100
150nH
150 200 250
FREQUENCY (MHz)
100nH
56nH
300
33nH
350 400 450 500
IMPEDANCE (R
DIFFERENTIAL OUTPUT
403 || – j610 (2.9pF)
384 || – j474 (2.4pF)
379 || – j381 (2.2pF)
380 || – j316 (2.1pF)
377 || – j253 (2.1pF)
376 || – j210 (2.0pF)
360 || – j177 (2.0pF)
22nH
5590 F09
IF
|| X
IF
(C
IF
CCIFA
))
has been laid out to accommodate this matching topology
with only minor modifications.
IF Amplifier Bias
The IF amplifier delivers excellent performance with V
= 3.3V, which allows a single supply to be used for V
V
limited by the output voltage swing. For higher P1dB, in
this case, resistor R2A (Figure 7) can be used to reduce
the output impedance and thus the voltage swing, thus
improving P1dB. The trade-off for improved P1dB will be
lower conversion gain.
With V
3dB, at the expense of higher power consumption. Mixer
P1dB performance at 900MHz is tabulated in Table 4 for
V
gain, high-Q wire-wound chip inductors are recommended
for L1A and L2A. Low cost multilayer chip inductors may
be substituted, with a slight reduction in conversion gain.
CCIF
CCIF
Figure 11. IF Output Return Loss with Lowpass Matching
. At V
values of 3.3V and 5V. For the highest conversion
CCIF
3.1 TO 5.3V
Figure 10. IF Output with Lowpass Matching
V
–10
–15
–20
–25
–30
CCIF
CCIFA
increased to 5V the P1dB increases by over
–5
0
50
= 3.3V, the RF input P1dB of the mixer is
C7A
68nH
22
100
L1A
IFA
FREQUENCY (MHz)
+
LTC5590
82nH + 1k
T1A
R2A
C9A
150
C5A
180nH
100nH
4:1
200
21
L2A
IFA
5590 F11
IFA
50
–
250
5590 F10
CC
CCIF
and
5590p