GPS/GNSS LNAs with Antenna Switch and Bias
MAX2674/MAX2676
7Maxim Integrated
Detailed Description
The MAX2674/MAX2676 are low-power LNAs designed
for GPS/GNSS receiver applications. The devices feature
low noise and high linearity in an ultra-small package.
They also include an antenna switch and circuitry sup-
porting bias to accommodate external LNA applications.
Input and Output Matching
To achieve optimal performance in noise figure, gain,
and IIP3, the devices require one matching inductor at
RFIN in series with a DC-blocking capacitor. RFOUT/
SHDN is internally matched to 50I, eliminating the need
for external matching components. At RFOUT/SHDN, an
external DC-blocking capacitor should be used to isolate
the shutdown control function.
Shutdown Mode
To place the device in shutdown mode, apply logic-low
to RFOUT/SHDN through a 25kΩ resistor. An additional
DC-blocking capacitor or component is required at
RFOUT/SHDN in this case. Apply a logic-high state or no
DC bias to turn the part permanently on.
DC Supply Decoupling and Layout
A properly designed PC board (PCB) is essential to any
RF microwave circuit. Use controlled-impedance lines
on all high-frequency inputs and outputs. Bypass VCC
with a decoupling capacitor located close to the device.
For long VCC lines, it may be necessary to add additional
decoupling capacitors. Locate these additional capaci-
tors further away from the device package.
Proper grounding of GND_ pins is essential. If the PCB
uses a top-side RF ground, connect it directly to the
GND_ pins. For a board where the ground is not on the
component layer, connect the GND_ pins to the board
with multiple vias close to the package.
Antenna Switch Control
The MAX2674/MAX2676 ANT input includes an autode-
tection feature. When no current is drawn from ANT, the
switch defaults to normal LNA operation. The pin can be
directly connected to an external active antenna. The
device automatically switches to the ANT input when an
external active antenna is connected.
Refer to www.maximintegrated.com for the MAX2674/
MAX2676 EV Kit schematic, layout files, BOM information,
and S-parameters.
Table 1. MAX2674 Typical Noise Parameters (VCC = 2.85V, TA = +25°C)
Table 2. MAX2676 Typical Noise Parameters (VCC = 2.85V, TA = +25°C)
FREQUENCY (MHz) NFMIN (dB) GAMMA_OPT MAG (°)GAMMA_OPT PHASE (°)Rn (I)
1550 0.651 0.446 44.1 8.33
1560 0.652 0.445 44.3 8.33
1570 0.654 0.445 44.6 8.32
1580 0.655 0.444 44.8 8.31
1590 0.656 0.444 45.1 8.3
1600 0.657 0.443 45.4 8.3
FREQUENCY (MHz) NFMIN (dB) GAMMA_OPT MAG (°)GAMMA_OPT PHASE (°)Rn (I)
1550 0.744 0.441 53.1 8.7
1560 0.746 0.44 53.4 8.68
1570 0.748 0.439 53.7 8.66
1580 0.75 0.438 54 8.65
1590 0.751 0.437 54.3 8.63
1600 0.753 0.436 54.7 8.62