LTC5590IUH#TRPBF Linear Technology, LTC5590IUH#TRPBF Datasheet - Page 15

• 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

applicaTions inForMaTion
IF Outputs
The IF amplifiers in channels A and B are identical. The IF
amplifier for channel A, shown in Figure 7, has differen-
tial open collector outputs (IFA
return pin (IFGNDA), and a pin for adjusting the internal
bias (IFBA). The IF outputs must be biased at the sup-
ply voltage (V
inductors L1A and L2A. Alternatively, the IF outputs can
be biased through the center tap of a transformer (T1A).
The common node of L1A and L2A can be connected to
the center tap of the transformer. Each IF output pin draws
approximately 48mA of DC supply current (96mA total).
An external load resistor, R2A, can be used to improve
impedance matching if desired.
IFGNDA (Pin 23) must be grounded or the amplifier will
not draw DC current. Inductor L3A may improve LO-IF
and RF-IF leakage performance in some applications, but
is otherwise not necessary. Inductors should have small
resistance for DC. High DC resistance in L3A will reduce
the IF amplifier supply current, which will degrade RF
performance.
L3A (OR SHORT)
Figure 7. IF Amplifier Schematic with Bandpass Match
100mA
23
LTC5590
CCIFA
), which is applied through matching
22
IFA
V
CCIFA
+
L1A
AMP
R2A
T1A
IF
C5A
C7A
+
L2A
4:1
and IFA
21
4mA
IFA
–
BIAS
–
IFA
20
), a DC ground
(OPTION TO
DC POWER)
V
REDUCE
IFBA
CCA
R1A
5590 F07
For optimum single-ended performance, the differential
IF output must be combined through an external IF
transformer or a discrete IF balun circuit. The evaluation
board (see Figures 1 and 2) uses a 4:1 IF transformer for
impedance transformation and differential to single-ended
conversion. It is also possible to eliminate the IF transformer
and drive differential filters or amplifiers directly.
At IF frequencies, the IF output impedance can be modeled
as 300Ω in parallel with 2.3pF . The equivalent small-signal
model, including bondwire inductance, is shown in Figure 8.
Frequency-dependent differential IF output impedance is
listed in Table 3. This data is referenced to the package
pins (with no external components) and includes the ef-
fects of IC and package parasitics.
Bandpass IF Matching
The bandpass IF matching configuration, shown in Figures
1 and 7, is best suited for IF frequencies in the 90MHz to
500MHz range. Resistor R2A may be used to reduce the IF
output resistance for greater bandwidth and inductors L1A
and L2A resonate with the internal IF output capacitance
at the desired IF frequency. The value of L1A, L2A can be
estimated as follows:
where C
L1A = L2A =
IF
is the internal IF capacitance (listed in Table 3).
Figure 8. IF Output Small-Signal Model
LTC5590


(
2πf
IF
22
)
0.9nH
IFA
2
1
• 2 • C
+
R IF
C IF
IF


21
IF A
0.9nH
–
LTC5590
5590 F08
15
5590p