9) Set DC supply to +5.0V, and set a current limit of

approximately 300mA, if possible. Disable the out-

put voltage and connect the supply to the EV kit

(through an ammeter, if desired). Enable the sup-

ply. Readjust the supply to get +5.0V at the EV kit.

There will be a voltage drop across the ammeter

when the mixer is drawing current.

10) Select LO1 by connecting LOSEL (TP3) to GND.

11) Enable the LO and the RF sources.

Testing the Mixer

Adjust the center and span of the spectrum analyzer to

observe the IF output tone at 160MHz. The level should

be approximately +2.0dBm (10dB conversion gain,

3dB pad loss). There is also a tone at 159MHz, which is

due to the LO signal applied to LO2. The amount of

suppression between the 160MHz and 159MHz signals

is the LO switch isolation. Note that the spectrum ana-

lyzer’s absolute magnitude accuracy is typically no bet-

ter than ±1dB. If accuracy is required, use the power

meter to measure the absolute single-tone power level.

Disconnect the GND connection to LOSEL. It is pulled

high by a pullup resistor on the board, selecting LO2.

Observe that the 159MHz signal increases while the

160MHz decreases. Reconfigure the test setup using a

combiner or hybrid to apply two RF signals at RFIN to

do a two-tone IP3 measurement, if desired. Terminate

the unused LO input in 50

Ω.

Detailed Description

The MAX9986 is a high-linearity downconverter inte-

grated with RF and LO baluns, an LO buffer, an IF

amplifier, and an SPDT LO input select switch. The EV

kit circuit consists mostly of supply-decoupling capaci-

tors, DC-blocking capacitors, an IF balun, and induc-

tive chokes. The MAX9986 EV kit circuit allows for thor-

ough analysis and a simple design-in.

Supply-Decoupling Capacitors

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 MAX9986 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 and IF Bias

Bias currents for the integrated IF amplifier and the LO

buffer are set with resistors R1 (953

Ω±1%) and R2

(619

Ω±1%), respectively. These values were carefully

chosen during factory testing for optimum linearity

and minimal supply current. The DC currents can be

reduced by increasing the values of R1 and R2, but the

device would operate at reduced performance levels

(see the Modifying the EV Kit section).

Current-Limiting Resistor

Resistor R3 is used for current limiting at the supply,

and typically dissipates 60mW.

Tap Network

Capacitor C5 helps to terminate the second-order inter-

modulation products.

LEXT

The 30nH wire-wound inductor, L3, improves LO-to-IF

and RF-to-IF isolation. If isolation is not critical, then this

pin can be grounded.

IF

±±

The MAX9986 employs a differential IF output to offer

increased IP2 system performance. The EV kit uses a

4:1 balun to transform the 200

Ω differential output

impedance to a 50

Ω single-ended output for easy

bench evaluation. Inductive chokes L1 and L2 provide

DC bias to the IF output amplifier, C13 and C14 for sup-

ply filtering, and R3 for current limiting.

As the differential IF outputs are relatively high imped-

ance (200

Ω), they are more susceptible to component

parasitics. It is often good practice to relieve the

ground plane directly underneath large components to

reduce associated shunt-C parasitics.

LOSEL

The EV kit includes a 47k

Ω pullup resistor 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 MAX9986 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.

MAX9986 Evaluation Kit

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