The MAX9985 high-linearity, dual-channel downconversion mixer is designed to provide approximately 6dB
gain, +28.5dBm of IIP3, and 10.5dB of noise figure (NF)
ideal for diversity receiver applications. With a 700MHz
to 1000MHz RF frequency range and a 570MHz to
865MHz LO frequency range, this mixer is ideal for lowside LO injection architectures. In addition, the broad
frequency range makes the MAX9985 ideal for GSM
850/950, 2G/2.5G EDGE, WCDMA, cdma2000
®
, and
iDEN®base-station applications.
The MAX9985 dual-channel downconverter achieves a
high level of component integration. The MAX9985 integrates two double-balanced active mixer cores, two LO
buffers, a dual-input LO selectable switch, and a pair of
differential IF output amplifiers. In addition, integrated
on-chip baluns at the RF and LO ports allow for singleended RF and single-ended LO inputs. The MAX9985
requires a typical 0dBm LO drive. Supply current is
adjustable up to 400mA.
The MAX9985 is available in a 36-pin thin QFN package (6mm x 6mm) with an exposed paddle. Electrical
performance is guaranteed over the extended temperature range, from TC= -40°C to +85°C.
, no input RF or LO signals applied, VCC= 4.75V to 5.25V, TC= -40°C to +85°C. Typical values
are at V
CC
= 5.0V, TC= +25°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VCCto GND...........................................................-0.3V to +5.5V
LO1, LO2 to GND ...............................................................±0.3V
Any Other Pins to GND...............................-0.3V to (V
CC
+ 0.3V)
RFMAIN, RFDIV, and LO_ Input Power ..........................+20dBm
RFMAIN, RFDIV Current (RF is DC shorted to GND through
Note 1: All limits reflect losses of external components. Output measurements taken at IF outputs of the
Typical Application Circuit
.
Note 2: Performance is guaranteed for f
RF
= 820MHz to 920MHz, fLO= 670MHz to 865MHz, and fIF= 100MHz. Operation outside
this range is possible, but with degraded performance of some parameters. See the
Typical Operating Characteristics
.
Note 3: Guaranteed by design and characterization.
Note 4: Measured with external LO source noise filtered so the noise floor is -174dBm/Hz. This specification reflects the effects of all
SNR degradations in the mixer including the LO noise, as defined in Maxim Application Note 2021.
Note 5: Measured at IF port at IF frequency. LOSEL may be in any logic state.
Note 6: Performance at T
C
= -40°C is guaranteed by design.
LO Switching Time
RF Input Impedance50Ω
LO Input Impedance50Ω
IF Output ImpedanceDifferential200Ω
RF Input Return LossLO on and IF terminated24dB
LO Input Return Loss
IF Return LossRF terminated in 50Ω20dB
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
50% of LOSEL to IF settled within 2 degrees
(Note 3)
1RFMAINMain Channel RF input. Internally matched to 50Ω. Requires an input DC-blocking capacitor.
2TAPMAINMain Channel Balun Center Tap. Bypass to GND with capacitors close to the pin.
3, 5, 7, 12,
20, 22, 24,
25, 26, 34
4, 6, 10, 16,
21, 30, 36
8TAPDIVDiversity Channel Balun Center Tap. Bypass to GND with capacitors close to the pin.
9RFDIVDiversity Channel RF Input. Internally matched to 50Ω. Requires an input DC-blocking capacitor.
11IFDBIAS
13, 14IFD+, IFD-
15LEXTD
17LODBIAS
18, 28N.C.No Connection. Not internally connected.
19LO1Local Osci l l ator 1 Inp ut. Thi s i np ut i s i nter nal l y m atched to 50Ω . Req ui r es an i np ut D C - b l ocki ng cap aci tor .
23LOSELLocal Oscillator Select. Set this pin to high to select LO1. Set low to select LO2.
27LO2Local Osci l l ator 2 Inp ut. Thi s i np ut i s i nter nal l y m atched to 50Ω . Req ui r es an i np ut D C - b l ocki ng cap aci tor .
29LOMBIAS
GNDGround
V
CC
Power Supply. Connect bypass capacitors as close to the pin as possible (see the TypicalApplication Circuit).
IF Diversity Amplifier Bias Control. Connect a 1.07kΩ resistor from this pin to ground to set the bias
current for the diversity IF amplifier (see the Typical Operating Characteristics for typical performance
versus resistor value).
Diversity Mixer Differential IF Output. Connect pullup inductors from each of these pins to V
the Typical Application Circuit).
Connect a 30nH inductor from this pin to ground to increase the RF-to-IF and LO-to-IF isolation.
Connect this pin to ground if isolations can be degraded (see the Typical Operating Characteristics
for typical degradation).
LO Diversity Amplifier Bias Control. Connect a 1.1kΩ resistor from this pin to ground to set the bias
current for the diversity LO amplifier (see the Typical Operating Characteristics for typical
performance versus resistor value).
LO Main Amplifier Bias Control. Connect a 1.1kΩ resistor from this pin to ground to set the bias
current for the main LO amplifier (see the Typical Operating Characteristics for typical performance
versus resistor value).
CC
(see
31LEXTM
32, 33IFM-, IFM+
35IFMBIAS
—EP
Connect a 30nH inductor from this pin to ground to increase the RF-IF and LO-IF isolation. Connect
this pin to ground if isolations can be degraded (see the Typical Operating Characteristics for typical
degradation).
Main Mixer Differential IF Output. Connect pullup inductors from each of these pins to V
Typical Application Circuit).
IF M ai n Am p l i fi er Bi as C ontr ol . C onnect a 1.07kΩ r esi stor fr om thi s p i n to g r ound to set the b i as cur r ent for
the m ai n IF am p l i fi er ( see the Typ i cal O p er ati ng C har acter i sti cs for typ i cal p er for m ance vs. r esi stor val ue) .
Exposed Paddle. Solder the exposed paddle to the ground plane using multiple vias. This paddle
affects RF performance and provides heat dissipation.
(see the
CC
MAX9985
Detailed Description
The MAX9985 is a dual-channel downconverter
designed to provide 6dB of conversion gain, +28.5dBm
input IP3, and +16.2dBm 1dB input compression point,
with a 10.5dB NF.
In addition to its high-linearity performance, the
MAX9985 achieves a high level of component integration. The device integrates two double-balanced active
mixers for two-channel downconversion. Both the main
and diversity channels include a balun and matching
circuitry to allow 50Ω single-ended interfaces to the RF
ports and the two LO ports. An integrated single-pole,
double-throw (SPDT) switch provides 50ns switching
time between the two LO inputs with 43dB of LO-to-LO
isolation and a -40dBm of LO leakage at the RF port.
Furthermore, the integrated LO buffers provide a high
drive level to each mixer core, reducing the LO drive
required at the MAX9985’s inputs to a -3dBm to +3dBm
range. The IF ports for both channels incorporate differential outputs for downconversion, which is ideal for
providing enhanced IIP2 performance.
Dual-channel downconversion makes the MAX9985
ideal for diversity receiver applications. In addition,
specifications are guaranteed over broad frequency
ranges to allow for use in GSM 850/950, 2G/2.5G
EDGE, WCDMA, cdma2000, and iDEN base stations.
The MAX9985 is specified to operate over a 700MHz to
1000MHz RF input range, a 570MHz to 865MHz LO
range, and a 50MHz to 250MHz IF range. The external
IF components set the lower frequency range (see the
Typical Operating Characteristics
for details).
RF Port and Balun
The RF input ports to both the main and diversity channels are internally matched to 50Ω, requiring no external matching components. A DC-blocking capacitor is
required as the input is internally DC-shorted to ground
through the on-chip balun. The RF port return loss is
typically 15dB over the entire 700MHz to 1000MHz RF
frequency range.
LO Inputs, Buffer, and Balun
The MAX9985 is optimized for a 570MHz to 865MHz
LO frequency range. As an added feature, the
MAX9985 includes an internal LO SPDT switch for use
in frequency-hopping applications. The switch selects
one of the two single-ended LO ports, allowing the
external oscillator to settle on a particular frequency
before it is switched in. LO switching time is typically
less than 50ns, which is more than adequate for typical
GSM applications. If frequency hopping is not
employed, simply set the switch to either of the LO
inputs. The switch is controlled by a digital input
(LOSEL), where logic-high selects LO1 and logic-low
selects LO2. LO1 and LO2 inputs are internally
matched to 50Ω, requiring only an 82pF DC-blocking
capacitor. To avoid damage to the part, voltage MUST
be applied to VCCbefore digital logic is applied to
LOSEL. Alternatively, a 1kΩ resistor can be placed in
series at the LOSEL to limit the input current in applications where LOSEL is applied before V
CC
.
The main and diversity channels incorporate a twostage LO buffer that allows for a wide-input power
range for the LO drive. All guaranteed specifications
are for an LO signal power from -3dBm to +3dBm. The
on-chip low-loss baluns, along with LO buffers, drive
the double-balanced mixers. All interfacing and matching components from the LO inputs to the IF outputs
are integrated on-chip.
High-Linearity Mixer
The core of the MAX9985 dual-channel downconverter
consists of two double-balanced, high-performance
passive mixers. Exceptional linearity is provided by the
large LO swing from the on-chip LO buffers. When combined with the integrated IF amplifiers, the cascaded
IIP3, 2RF-2LO rejection, and NF performance are typically +28.5dBm, 77dBc, and 10.5dB, respectively.
Differential IF
The MAX9985 has a 50MHz to 250MHz IF frequency
range, where the low-end frequency depends on the
frequency response of the external IF components. Note
that these differential ports are ideal for providing
enhanced IIP2 performance. Single-ended IF applications require a 4:1 (impedance ratio) balun to transform
the 200Ω differential IF impedance to a 50Ω singleended system. After the balun, the IF return loss is better than 20dB. The user can use a differential IF
amplifier on the mixer IF ports, but a DC block is
required on both IFD+/IFD- and IFM+/IFM- ports to keep
external DC from entering the IF ports of the mixer.
Applications Information
Input and Output Matching
The RF and LO inputs are internally matched to 50Ω.
No matching components are required. Return loss at
the RF port is typically 15dB over the entire input range
and return loss at the LO ports are typically 25dB. RF
and LO inputs require only DC-blocking capacitors for
interfacing.
The IF output impedance is 200Ω (differential). For
evaluation, an external low-loss 4:1 (impedance ratio)
balun transforms this impedance to a 50Ω single-ended
output (see the
Typical Application Circuit
).
Dual, SiGe, High-Linearity, 700MHz to 1000MHz
Downconversion Mixer with LO Buffer/Switch
Bias currents for the two on-chip LO buffers is optimized by fine-tuning the off-chip resistors on LODBIAS
(pin 17) and LOMBIAS (pin 29). The current in the
buffer amplifiers is reduced by increasing the value of
these resistors, but performance may degrade. See the
Typical Operating Characteristics
for key performance
parameters versus this resistor value. Doubling the
value of these resistors reduces the total chip current
by approximately 50mA (see Table 1).
IF Amplifier Bias Resistors
Bias currents for the two on-chip IF amplifiers are optimized by fine-tuning the off-chip resistors on IFDBIAS
(pin 11) and IFMBIAS (pin 35). The current in the IF
amplifiers is decreased by raising the value of these
resistors, but performance may degrade. See the
Typical Operating Characteristics
for key performance
parameters versus this resistor value. Doubling the
value of this resistor reduces the current in each IF
amplifier from 100mA to approximately 50mA (see
Table 1).
LEXT Inductor
Short LEXT_ to ground using a 0Ω resistor. For applications requiring improved RF-to-IF and LO-to-IF isolation,
LEXT_ can be used by connecting a low-ESR inductor
from LEXT_ to GND. See the
Typical Operating
Characteristics
on RF-to-IF port isolation and LO-to-IF
port leakage for various inductor values. The load
impedance presented to the mixer must be such that
any capacitance from both IF- and IF+ to ground do not
exceed several picofarads to ensure stable operating
conditions.
Approximately 100mA flows through LEXT_, so it is
important to use a low-DCR wire-wound inductor.
Layout Considerations
A properly designed PCB is an essential part of any
RF/microwave circuit. Keep RF signal lines as short as
possible to reduce losses, radiation, and inductance.
For the best performance, route the ground pin traces
directly to the exposed paddle under the package. The
PCB exposed paddle MUST be connected to the
ground plane of the PCB. It is suggested that multiple
vias be used to connect this paddle to the lower-level
ground planes. This method provides a good RF/thermal-conduction path for the device. Solder the exposed
paddle on the bottom of the device package to the
PCB. Refer to the
MAX9985 Evaluation Kit
as a reference for board layout. Gerber files are available upon
request at www.maxim-ic.com.
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for highfrequency circuit stability. Bypass each V
CC
pin and
TAPMAIN/TAPDIV with the capacitors shown in the
Typical Application Circuit
(see Table 2 for component
values). Place the TAPMAIN/TAPDIV bypass capacitor
to ground within 100 mils of the pin.
Exposed Paddle RF/Thermal
Considerations
The exposed paddle (EP) of the MAX9985’s 36-pin thin
QFN-EP package provides a low thermal-resistance
path to the die. It is important that the PCB on which the
MAX9985 is mounted be designed to conduct heat
from the EP. In addition, provide the EP with a lowinductance path to electrical ground. The EP MUST be
soldered to a ground plane on the PCB, either directly
or through an array of plated via holes.
Table 2. Component Values
COMPONENTVALUEDESCRIPTION
C1, C2, C7, C839pFMicrowave capacitors (0402)
C3, C60.033µFMicrowave capacitors (0603)
C4, C5—Not used
C9, C13, C15,
C17, C18
C10, C11, C12,
C19, C20, C21
C14, C1682pFMicrowave capacitors (0402)
L1, L2, L4, L5560nH
L3, L630nH
R1, R41.07kΩ±1% resistors (0402)
R2, R51.1kΩ±1% resistors (0402)
R3, R60ΩResistors (1206)
T1, T24:1
U1—MAX9985 IC
0.01µFMicrowave capacitors (0402)
150pFMicrowave capacitors (0603)
Wire-wound high-Q inductors
(0805)
Wire-wound high-Q inductors
(0603)
Transformers (200:50)
Mini-Circuits TC4-1W-7A
MAX9985
Dual, SiGe, High-Linearity, 700MHz to 1000MHz
Downconversion Mixer with LO Buffer/Switch
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________