nulling. In addition, the LO signal reflected at the I/Q IF

port produces a residual DC term that can disturb the

nulling condition.

As shown in Figure 1, providing an RC termination on

each of the I+, I-, Q+, Q- ports reduces the amount of

LO leakage present at the RF port under varying temp-

erature, LO frequency, and baseband drive conditions.

Note that the resistor value is chosen to be 100Ω with a

corner frequency 1 / (2πRC) selected to adequately filter

of the baseband response at the highest baseband

I+/I- and Q+/Q- effectively see the RC networks and

thus become terminated in 50Ω (R/2). The RC network

The MAX2021 EV kit includes flexibility for a diplexer

network to be installed if desired. See Figure 3 for

details on the EV kit schematic.

Layout Considerations

The MAX2021 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

MAX2021 package’s 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 PCB ground plane with a low ther-

mal and electrical impedance contact. Ideally, this is

achieved by soldering the backside of the package

directly to a top metal ground plane on the PCB.

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 MAX2021 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.

MAX2021 Evaluation Kit

4

_______________________________________________________________________________________

C = 6.8pF

C = 6.8pF

100Ω

C = 6.8pF

100Ω

L = 40nH

MAX2021

RF MODULATOR

0°

90°

LO

∑

C = 6.8pF

L = 40nH

I

Q

100Ω

100Ω

RF

Figure 1. Example Diplexer Network for GSM 900 Applications