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 200MHz. The level should
be about +0.3dBm (8.3dB conversion gain, 3dB pad
loss). There is also a tone at 199MHz, which is due to
the LO signal applied to LO2. The amount of suppres-
sion between the 200MHz and 199MHz signals is the
LO switch isolation. Note that the spectrum analyzer’s
absolute magnitude accuracy is typically no better 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 199MHz signal increases while the
200MHz 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 50Ω.
Detailed Description
The MAX9994 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 MAX9994 EV kit circuit allows for thor-
ough 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 MAX9994 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 and IF Bias
Bias currents for the integrated IF amplifier and the LO
buffer are set with resistors R1 (806Ω, ±1%) and R2
(549Ω, ±1%), respectively. These values were carefully
chosen during factory testing for optimum linearity and
minimal supply current.
Current-Limiting Resistors
Resistor R3 is used for current limiting at the supply.
Resistor R3 typically dissipates 60mW.
Tap Network
Capacitor C5 helps to terminate the second-order inter-
modulation products.
LEXT
The 10nH 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 MAX9994 employs a differential IF output to offer
increased IP2 system performance. The EV kit uses a
4:1 balun to transform the 200Ω differential output
impedance to a 50Ω single-ended output for easy
bench evaluation. Inductive chokes L1 and L2 provide
DC bias to the IF output amplifier, C13 and C14 for
supply filtering, and R3 for current limiting.
As the differential IF outputs are relatively high imped-
ance (200Ω), 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 47kΩ 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 MAX9994 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 MAX9994 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 MAX9994
package exposed paddle (EP) conducts heat from the
device and provides a low-impedance electrical connec-
tion to the ground plane. The EP MUST be attached to
the PC board ground plane with a low-thermal and elec-
trical impedance contact. Ideally, this is achieved by sol-
dering 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
Evaluates: MAX9994
MAX9994 Evaluation Kit
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