get an accurate output power measurement.
Disconnect the GND connection to LOSEL. It will be
pulled high by a pullup resistor on the board. This
selects LO1. Observe the new IF output at 200MHz.
Reconfigure the test setup using a combiner or hybrid
to sum the two RF inputs to do a two-tone IP3 measure-
ment, if desired. Terminate the unused LO input in 50
Ω
.
Detailed Description
The MAX9995 is a highly integrated dual downconvert-
er; RF and LO baluns are integrated on-chip, as well as
two double-balanced mixers, two IF amplifiers, an LO
buffer, and a single-pole/double throw (SPDT) LO input
select switch. The EV kit circuit consists mostly of sup-
ply decoupling capacitors and DC-blocking capacitors,
making for a simple design-in.
DC-Blocking Capacitors
The MAX9995 has internal baluns on the RFMAIN,
RFDIV, LO1, and LO2 inputs. These inputs have almost
0
Ω
resistance at DC, so DC-blocking capacitors C1,
C8, C14, and C16 are used to prevent any external
bias from being shunted directly to ground. Capacitors
C10, C11, C19, and C20 are used to keep DC current
from flowing into the transformer, as well as providing
the flexibility for matching.
LO Buffer and IF Amplifier Bias
Bias currents for the integrated LO buffers and the IF
output amplifiers are set with resistors R2, R5, and R1,
R4, respectively. These values were carefully chosen
for best linearity and lowest supply current through test-
ing at the factory. Changing these values, or using
lower tolerance resistors, degrades performance. If
lower currents are desired, consult the factory for opti-
mum resistor settings.
Current-Limiting Resistors
Resistors R3 and R6 are used for current limiting at the
supply. These resistors typically dissipate 50mW each.
TAP Network
The network at TAP formed by C2, C3, C6, and C7
helps to terminate the second-order intermodulation
products at the RF inputs.
IND_EXT
The 10nH wire-wound inductors L3 and L6 improve LO-
to-IF and RF-to-IF isolation. If isolation is not critical,
then the corresponding pins can be grounded.
IF Outputs
The MAX9995 employs a differential IF output to offer
increased IP2 system performance. For convenience,
the EV kit uses a 4:1 balun to transform the 200
Ω
differ-
ential output impedance to a 50
Ω
single-ended output.
Inductive pullups provide DC bias to the IF output
amplifiers. Series capacitors C10, C11, C19, and C20
work in conjunction with the inductors and the 4:1 balun
transformers (T1 and T2) to match the IF outputs for
200MHz operation.
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 (see Figure 6).
LOSEL
The EV kit includes a 47k
Ω
pullup resistor for easy
selection of the LO port. Providing a ground at TP3
selects LO2, and leaving TP3 open selects LO1. To
drive TP3 from an external source, follow the limits
called out in the MAX9995 device data sheet. Do not
apply logic voltages to TP3 without the +5V supply
applied. Doing so can cause the on-chip ESD diodes to
conduct and could damage the part.
Evaluates: MAX9995
MAX9995 Evaluation Kit
_______________________________________________________________________________________
3
EQUIPMENT
QTY
DESCRIPTION
HP E3631A
1
DC power supply
Fluke 75 Series II
1
Digital multimeter (ammeter)
HP/Agilent 8648B
3
RF signal generators
HP 437B
1
RF power meter
HP 8561
1
Spectrum analyzer
HP 8482A
1
High-power sensor (power
head)
3dB pad
4
3dB attenuators
50
Ω
termination
1
50
Ω
(1W) termination
Table 1. Test Equipment