Rainbow Electronics MAX2690 - Manual (Page 7)

MAX2690
Low-Noise, 2.5GHz
Downconverter Mixer
_______________________________________________________________________________________ 7
______________________________________________________________Pin Description
PIN
Inductive Degeneration Pin. For maximum linearity, connect LGND directly to ground with no series induc-
tance. Trade off linearity for gain by increasing the series inductance from LGND to ground. See the
Applications Information section for more information.
LGND 1
FUNCTION NAME
RF Ground. This pin must have a separate via to the ground plane, as close to the pin as possible to
minimize inductance.
GND 2
RF Bypassing Capacitor Pin. Bypass RFBYP with an appropriate-value capacitor (typically 1000pF) to ground. RFBYP 4
RF Input Port. RF Input of Downconverter Mixer. See the Applications Information section for details on
matching to RFIN.
RFIN 3
Local-Oscillator Input. LO should be AC coupled and presents a 50
Ω
load impedance. See the Applications
Information section for more information.
LO 6
Differential IF Inverting Output. IFOUT- is an open-collector output and must be pulled up to V CC with an
external inductor for proper biasing. A resistor in parallel with the inductor may also be used to set a termi-
nating impedance. See the
Typical Operating Characteristics section for a plot of IF port characteristics vs.
frequency (see plot titled Single-Ended IF Port Equivalent Shunt RC Network).
IFOUT- 8
Ground for the LO Port. This pin must have its own via to the ground plane, as close as possible to the pin to
minimize inductance.
GNDLO 7
Supply-Voltage Input, +2.7V to +5.5V. Connect 0.1µF and 1000pF capacitors (in parallel) between V CC
and GND.
V CC 5
Active-Low Shutdown Input. A digital logic-low level at SHDN deactivates all part functions and reduces the
supply current to typically 0.4µA.
SHDN 10
Differential IF Noninverting Output. IFOUT+ is an open-collector output and must be pulled up to V CC with
an external inductor for proper biasing. A resistor in parallel with the inductor may also be used to set a ter-
minating impedance. See the
Typical Operating Characteristics section for a plot of IF port characteristics
vs. frequency (see plot titled Single-Ended IF Port Equivalent Shunt RC Network).
IFOUT+ 9
_______________Detailed Description
The MAX2690 is a 2.5GHz, double-balanced downcon-
verter mixer designed to provide optimum intermodula-
tion performance for a given supply current. It consists
of a double-balanced Gilbert-cell mixer with single-
ended RF and LO port connections, and a differential
IF port. An on-chip bias cell provides a low-power shut-
down feature.
RF Input
The RFIN and RFBYP pins form the MAX2690’s RF
input. The single-ended RF input signal is applied to
the RFIN pin (refer to the RF Port Impedance vs.
Frequency graph in the
Typical Operating Character-
istics ). The RFBYP pin should be AC grounded typically
with a 1000pF capacitor. This capacitor value should
present a low impedance at both the RF and IF
frequencies.
IF Output
The IFOUT+ and IFOUT- pins form the MAX2690’s differ-
ential open-collector IF output. The IF output is coupled to
the load using shunt inductors to V
CC and series capaci-
tors to the load. Most applications use a resistive termina-
tion of 500
Ω
(typical) resistors in parallel with the pull-up
inductors to set a terminating impedance. The part’s con-
version gain has been specified with the resistors in place
(using the output network on the MAX2690 EV kit),
accounting for a 3dB loss due to the resistors. Therefore,
it is possible to achieve an increase in gain with a proper-
ly designed matching network. However, the resistors
provide for minimum passband ripple when this port is
connected to typical IF filters.
Bias
The bias cell includes compensation circuitry to mini-
mize conversion-gain variations over temperature as
well as shutdown control circuitry. The SHDN pin can
be used to disable all functions and reduce supply cur-
rent to typically 0.4µA.