Detailed Description
The MAX2041 is a high-linearity up/downconverter inte-
grated with RF and LO baluns, an LO buffer, and an
SPDT LO input select switch. The EV kit circuit uses the
MAX2041 and consists mostly of supply-decoupling
capacitors, DC-blocking capacitors, a current-setting
resistor, and an IF balun. The MAX2041 EV kit circuit
allows for thorough analysis and a simple design-in.
Supply-Decoupling Capacitors
Capacitors C2, C6, C7, and C8 are 22pF supply-
decoupling capacitors used to filter high-frequency
noise. Capacitors C3, C9, and C11 are larger 0.01µF
used for filtering lower frequency noise on the supply.
DC-Blocking Capacitors
The MAX2041 has internal baluns at the RF and LO
inputs. These inputs have almost 0Ω resistance at DC,
and so DC-blocking capacitors C1, C10, and C12 are
used to prevent any external bias from being shunted
directly to ground.
LO Bias
Bias current for the integrated LO buffer is set with
resistor R1 (549Ω ±1%). The DC current of the device
can be reduced by increasing the value of R1 but the
device would operate at reduced performance levels
(see the Modifying the EV Kit section).
Tap Network
Capacitor C5 helps to terminate the second-order inter-
modulation products.
IF±
The MAX2041 mixer has an IF frequency range of DC
to 350MHz. Note that these differential ports are ideal
for providing enhanced IIP2 performance. Single-
ended IF applications require a 1:1 balun to transform
the 50Ω differential output impedance to a 50Ω single-
ended output. After the balun, the IF return loss is bet-
ter than 15dB. The differential IF is used as an input
port for upconverter operation. The user can use a dif-
ferential IF amplifier following the mixer, but a DC block
is required on both IF pins. In this configuration, the IF+
and IF- pins need to be returned to ground through a
high resistance (about 1kΩ). This ground return can
also be accomplished by grounding the RF tap (pin 3)
and AC-coupling the IF+ and IF- ports (pins 19 and 18).
LOSEL
The EV kit includes a 47kΩ pullup resistor (R2) for easy
selection of the LO port. Providing a ground at TP3
selects LO1, and leaving TP3 open selects LO2. To
drive TP3 from an external source, follow the limits
called out in the MAX2041 device data sheet. Logic
voltages should not be applied to LOSEL without the
+5V supply voltage. Doing so can cause the on-chip
ESD diodes to conduct and could damage the device.
Layout Considerations
The MAX2041 evaluation board can be a guide for your
board layout. Pay close attention to thermal design
and close placement of components to the IC. The
MAX2041 package exposed paddle (EP) conducts
heat from the device and provides a low-impedance
electrical connection to the ground plane. The EP must
be attached to the PC board ground plane with a low
thermal and electrical impedance contact. Ideally, this
is achieved by soldering the backside of the package
directly to a top metal ground plane on the PC board.
Alternatively, the EP can be connected to an internal or
bottom-side ground plane using an array of plated vias
directly below the EP. The MAX2041 EV kit uses nine
evenly spaced 0.016in-diameter, plated through holes
to connect the EP to the lower ground planes.
Depending on the ground-plane spacing, large sur-
face-mount pads in the IF path may need to have the
ground plane relieved under them to reduce parasitic
shunt capacitance.
Modifying the EV Kit
The RF, LO, and IF ports are broadband matched, so
there is no need to modify the circuit for use anywhere
in the 1700MHz to 3000MHz RF range, 1900MHz to
3000MHz LO range, and 50MHz to 350MHz IF range.
The DC current of the device can be reduced if reduced
performance is acceptable. Reducing the current is
accomplished by increasing the value of R1. Doubling
the value of R1 reduces the DC current approximately
in half. Approximately 10% of the overall IC current is
used for basic operation of the device (R1 set at 549Ω)
and cannot be reduced.
Evaluates: MAX2041
MAX2041 Evaluation Kit
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