Testing the Mixer

Adjust the center and span of the spectrum analyzer to

observe the RF output tone at 810MHz for upconverter

operation. The level should be about -10dBm (7dB con-

version loss, 3dB pad loss). The spectrum analyzer’s

absolute magnitude accuracy is typically no better than

±1dB.

Disconnect the GND connection to LOSEL. It will be

pulled high by a pullup resistor on the board, selecting

LO2. Observe that the 809MHz signal increases while

the 810MHz decreases.

Reconfigure the test setup using a combiner or hybrid to

sum two of the frequency sources to do a two-tone IP3

measurement if desired. Terminate the unused LO input

in 50

Ω.

Detailed Description

The MAX2031 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

MAX2031 and consists mostly of supply-decoupling

capacitors, DC-blocking capacitors, a current-setting

resistor, and an IF balun. The MAX2031 EV kit circuit

allows for thorough analysis and a simple design-in.

Supply-Decoupling Capacitors

C2, C7, C8, and C11 are 82pF supply-decoupling

capacitors used to filter high-frequency noise. C3, C6,

and C9 are larger 0.01µF capacitors used for filtering

lower frequency noise on the supply.

DC-Blocking Capacitors

The MAX2031 has internal baluns at the RF and LO

inputs. These inputs have almost 0

Ω resistance at DC,

so DC-blocking capacitors C1, C10, and C12 are used

to prevent any external bias from being shunted directly

to ground.

LO Bias

The bias current for the integrated LO buffer is set with

resistor R1 (523

Ω ±1%). Increasing the value of R1 can

reduce the DC current of the device but the device

would operate at reduced performance levels (see the

Modifying the EV Kit section).

TAP Network

The TAP pin for the internal balun is grounded.

IF±

The MAX2031 mixer has a DC to 250MHz IF frequency

range. Note that these differential ports are ideal for

providing enhanced IIP2 performance. Single-ended IF

applications require a 1:1 balun to transform the 50

Ω

differential IF impedance to 50

Ω single-ended. After the

balun, the IF return loss is better than 15dB. The differ-

ential IF is used as an input port for upconverter opera-

tion. The user can use a differential IF amplifier follow-

ing the mixer but a DC block is required on both IF

pins.

Tuning Networks

The performance of the MAX2031 is enhanced with the

addition of external tuning networks. Capacitor C4 and

inductor L1 form a bandpass filter network that enhances

the linearity performance when the mixer is used to

upconvert an IF port signal to the RF port. This network is

constructed on the kit and limits the usable RF band-

width to approximately 750MHz to 850MHz (refer to the

MAX2031 data sheet). This network can be tuned to

accommodate other RF bands if desired.

Capacitor C5 is used to improve the linearity perfor-

mance of the MAX2031 when the mixer is used to

downconvert an RF port signal to the IF port. The value

of this cap could change slightly depending on the RF

and LO frequencies.

Capacitor C5 is not required for upconverter operation

and the C4/L1 network is not required for downconverter

operation.

LOSEL

The EV kit includes a 47k

Ω 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 MAX2031 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 MAX2031 evaluation board can be a guide for board

layout. Pay close attention to thermal design and close

placement of components to the IC. The MAX2031 pack-

age 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

MAX2031 EV kit uses nine evenly spaced, 0.016in-diam-

eter, 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

MAX2031 Evaluation Kit

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