MAX1479_1 Datasheet, PDF (3/6 Pages) Maxim Integrated Products – Evaluation Kit

MAX1479 Evaluation Kit
Layout Issues
A properly designed PC board is an essential part of any
RF/microwave circuit. On high-frequency inputs and out-
puts, use controlled-impedance lines and keep them as
short as possible to minimize losses and radiation. At
high frequencies, trace lengths that are on the order of
λ/10 or longer can act as antennas.
Keeping the traces short also reduces parasitic induc-
tance. Generally, 1in of a PC board trace adds about
20nH of parasitic inductance. The parasitic inductance
can have a dramatic effect on the effective inductance.
For example, a 0.5in trace connecting a 100nH inductor
adds an extra 10nH of inductance or 10%.
To reduce the parasitic inductance, use wider traces
and a solid ground or power plane below the signal
traces. Also, use low-inductance connections to ground
on all GND pins, and place decoupling capacitors
close to all VDD connections.
The EV kit PC board can serve as a reference design
for laying out a board using the MAX1479.
Detailed Description
Power-Down Control
The MAX1479 can be controlled externally using the
ENABLE connector. The IC draws approximately 0.2nA
(at room temperature) in shutdown mode. Jumper JU1
is used to control this mode. The shunt can be placed
between pins 1 and 2 to enable the device. Remove
the JU1 shunt for external control. See Table 1 for
jumper function descriptions.
Table 1. JU1 Through JU4 Jumpers
Function
JUMPER
JU1
STATE
1-2
2-3
N.C.
FUNCTION
RF carrier transmit enable
Power-down mode
External power-down control
1-2
RF carrier transmit mode (ASK),
FSK high frequency (FSK)
JU2
2-3
PA off, PLL ON (ASK),
FSK low frequency (FSK)
N.C. External data transmit
1-2 External supply operation
JU3
2-3 Battery operation
1-2 FSK mode
JU4
2-3 ASK mode
Data Input
The MAX1479 EV kit transmits ASK and FSK data with
data rates of up to 100kbps (ASK) or 20kbps (FSK).
JU2 controls whether the MAX1479 transmits the ASK
carrier frequency (or the FSK high frequency), turns off
the PA (or transmits the FSK low frequency), or trans-
mits an external data stream. See Table 1.
REF_IN External Frequency Input
For applications where the correct frequency crystal is
not available, it is possible to directly inject an external
frequency through the REF_IN SMA (not provided).
Connect the SMA to a low-phase-noise generator. The
addition of C18 and C19 is necessary (use 0.01µF
capacitors).
Battery Operation
The MAX1479 EV kit can be powered by an external
power supply or by the supplied 3V coin-cell battery. Set
jumper JU3 to connect pins 2 and 3 for battery operation.
RF Output
The MAX1479 EV kit includes two SMA connectors for
RF output. RF_OUT is a standard SMA and is used to
connect the PA output to test equipment. Output is
matched to 50Ω. ANTENNA_OUT is a reverse polarity
SMA and is used to connect to the 1/4-wave whip
antenna (not supplied). Note that resistor R2 (0Ω)
needs to be added.
Modulation Mode Input
Jumper JU4 sets the mode of transmission. Set jumper
JU4 to connect pins 1 and 2 for FSK mode, 2 and 3 for
ASK mode.
FSK Frequency Deviation
The FSK deviation is set by jumpers JU5 through JU7.
The maximum deviation depends on the PC board para-
sitics. The EV kit max is around 50kHz (315MHz). If very
large FSK frequency deviations are desired, use a crystal
with a larger motional capacitance and/or reduce PC
board parasitic capacitances. One way to reduce para-
sitic capacitances on the EV kit is to remove C14, C15,
and C16 and move the crystal closer to the IC.
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