200mW Single-Chip Transmitter ICs for
868MHz/915MHz ISM Bands
used on the EV kit board for +23dBm output power at
4.5V, and 22kΩ is also recommended for +20dBm out-
put power at +3.0V. For +17dBm at 3.0V, 36kΩ is rec-
ommended. The current consumption, efficiency, and
distortion in the amplification chain are affected by the
choice of the resistor RPWRSET, offering a lot of design
flexibility.
TO VREG
(2.1V)
TO INTERNAL
CONTROL
CIRCUIT
The RLPF pin sets the bandwidth of the modulation fil-
ter. The default filter bandwidth, obtained with a 68kΩ
resistor, is for 1.2Mchips/s. The bandwidth is increased
to accommodate 5Mchips/s by decreasing the resistor
value to about 26kΩ. The minimum value for the resistor
is 12kΩ, which generates the maximum filter band-
width. A higher value can be used in FM mode to set
up a slow ramp-up time for the PA.
MAX2900–MAX2904
Data Filter Characteristics
The data filter approximates a 3rd-order Butterworth fil-
ter. The 3dB cut-off frequency is adjusted through the
resistor on pin RLPF, which controls the first two poles
of the filter (the last high-frequency pole is fixed and set
around 10MHz). The filter is adjustable in a range from
approximately 700kHz to 7MHz.
With the nominal setting (3dB cut off at 0.8MHz), the fil-
ter attenuation is 10dB at 3.6MHz. If used with a BPSK
at 1.22MHz, this provides about 30dB of modulation
rolloff at 3.6MHz. Hence, a significant channelization
effect is obtained.
In the wideband setting (3dB cut off at 5MHz), the
attenuation at 30MHz is still 30dB, helping to pass the
FCC spurious emissions at 960MHz.
PIN
VASK
>200kΩ
INTERNAL
CIRCUITS
EXTERNAL
RESISTOR
BRIDGE
1.5V
Figure 2. PIN VASK Equivalent Circuit
The VASK pin is an input to the internal gain control cir-
cuitry. The gain control is greater than 30dB over the
full range of input voltages from 0 to VREG = 2.1V. This
input is used for ASK modulation. At 1V, a typical 15dB
attenuation is obtained from the peak power. When this
input is not used, connect VASK to VREG.
The RLPF input controls the modulation filter center fre-
quency.
TO INTERNAL
CONTROL
CIRCUIT
PIN RLPF
100Ω
1.2V
INTERNAL
CIRCUITS
EXTERNAL
RESISTOR
Figure 3. PIN RLPF Equivalent Circuit
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
