Low-Noise Amplifier (LNA)

MAX2685.

2) Connect the GAIN jumper (JU1) on the EV kit to the

high-gain mode.

3) Connect a 3V DC supply (through an ammeter, if

4) Connect one RF signal generator to the LNAIN SMA

connector. Do not turn on the generator’s output. Set

the generator for an output frequency of 880MHz

and a power level of -30dBm.

5) Connect a spectrum analyzer to the LNAOUT SMA

connector on the EV kit. Set the spectrum analyzer

to a center frequency of 880MHz, a total span of

200MHz, and a reference level of 0dBm.

6) Turn on the DC supply. The supply current should

read approximately 8.5mA (if using an ammeter).

7) Activate the RF generator’s output. An 880MHz sig-

nal should show on the spectrum analyzer’s display

and should indicate a typical gain of 15dB after

accounting for cable losses.

8) Test the MAX2685’s low gain mode by changing the

output power on the signal generator to -10dBm and

setting the GAIN jumper (JU1) on the EV kit to the

“LO” position, GAIN = GND. The supply current

should read approximately 4mA (if using an amme-

ter). An 880MHz signal should show on the spectrum

analyzer’s display and should indicate an attenuation

of 12dB after accounting for cable losses.

9) If desired, test the shutdown feature by moving the

SHDN jumper (JU1) into the “OFF” position. This dis-

ables the part and reduces supply current below

1.0µA.

Downconverter Mixer

1) Connect the GAIN jumper (JU1) on the EV kit to the

high-gain mode.

2) Remove the RF signal generator and spectrum ana-

lyzer from the LNAIN and LNAOUT connections. The

DC supply connections needed for testing the mixer

are the same as in the LNA section.

3) Connect one RF signal generator (with the output

disabled) to the LO SMA connector. Set the frequen-

cy to 960MHz and the output power to -8dBm.

4) Connect the other RF signal generator (with the out-

put disabled) to the MIXIN SMA connector. Set the

frequency to 880MHz and the amplitude to -25dBm.

5) Connect the spectrum analyzer to the IFOUT+ SMA

connector. Set the spectrum analyzer to an 80MHz

center frequency, a 1MHz span, and a 0dBm refer-

ence level.

6) Turn on the LO and RF signal generators.

7) An 80MHz signal should show on the spectrum ana-

lyzer’s display and should indicate a typical gain of

6.1dB after accounting for cable losses.

8) If desired, connect the GAIN jumper (JU1) on the EV

kit to the “LO” position, GAIN = GND. This places

the mixer in low-gain mode. An 80MHz signal should

appear on the spectrum analyzer’s display and

should indicate a typical gain of 4.6dB after

accounting for cable losses.

Detailed Description

The MAX2685 EV kit’s circuitry is described in this sec-

tion. For more detailed information about the operation of

the device itself, refer to the MAX2685 data sheet.

Low-Noise Amplifier

The LNA circuitry consists of matching networks and

DC-blocking capacitors at the input and output.

Downconverter Mixer RF Input

The downconverter mixer’s RF input, MIXIN, requires a

simple matching network. C10 provides DC blocking,

and C9 is used to match the input to 50

Ω at 880MHz.

Downconverter Mixer LO Input

The downconverter mixer’s LO input is terminated with

a 75

Ω resistor, R3, at the SMA input. C8 provides DC

blocking.

Downconverter Mixer

Differential IF Output

The mixer output can be evaluated in either a single-

ended or differential configuration. The MAX2685 EV kit

is shipped with a differential to single-ended converter

for single-ended testing. See the

IF Output Configuration

section.

MAX2685 Evaluation Kit

2

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