MAX7060ATG/V+ Maxim Integrated Products, MAX7060ATG/V+ Datasheet - Page 19

• Manufacturer Part Number: MAX7060ATG/V+
• Description: RF Transmitter 300MHz to 450MHz Fre quency-and-Output-Po
• Manufacturer: Maxim Integrated Products

Specifications of MAX7060ATG/V+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

At data rates higher than 30kbps Manchester (60kbps
NRZ), it may be necessary to shape the ASK transmitter
pulses to reduce the occupied bandwidth of the trans-
mitted signal to comply with government regulations
(FCC in the U.S., ETSI in Europe). There is no shaping
of the FSK modulation. The MAX7060 has two forms of
amplitude shaping: digital and analog.
The digital shaping feature allows the user to choose a
linear stairstep function to increase and decrease the
power when the PA is turned on and off for an ASK bit
interval. There are three registers that control the digital
amplitude shaping settings. The first setting is the final
power of the PA when the pulse reaches its maximum
(PApwr register). The second setting is the amplitude
change, in decibels, for each step, which is the vertical
axis of the stairstep (PAstep register). The third setting
is the time interval of each step, which is the horizontal
axis of the stairstep (Tstep register). The final power set-
ting (decimal 0 to 30 in increments of 1dB) is entered in
the PApwr register. The amplitude step (decimal 0 to 30
in increments of 1dB) is entered in the PAstep register.
The time interval (decimal 0 to 60/f
4/f
shape an 80kbps NRZ data stream (12.5Fs bit interval),
the user might choose a maximum power level of 0x1E
(30dec), an amplitude step of 5dB, and a time interval
of 0.5Fs assuming a crystal frequency of 16MHz. This
would produce an ASK pulse that ramps up in 3Fs, lev-
els off for 9.5Fs, and ramps down in 3Fs. Because the
amplitude steps are in decibels, the shape of the pulse
Figure 7. Digital Amplitude Shaping Timing Diagram
0x1E (30dec)
XTAL
PApwr =
DIN
) is entered in the Tstep register. For example, to
0
Tstep = 0x2 (0.5µs)
______________________________________________________________________________________
Digital Amplitude Shaping
ASK Amplitude Shaping
280MHz to 450MHz Programmable
Tstep = 0x2 (0.5µs)
XTAL
in increments of
12.5µs
PAstep = 0x05 (5dB)
PAstep = 0x05 (5dB)
rise and fall is exponential on a linear display (an oscil-
loscope, for instance). Because most ASK receivers use
a logarithmic amplitude detector, the demodulated pulse
has a linear ramp shape. The digital shaping is disabled
when the Tstep register is 0x00.
To use the analog shaping feature, the user must con-
nect the bias inductor to the ROUT pin instead of directly
to the PAVOUT pin. This places a MOS resistor between
PAVOUT and PAOUT, which slows down the applica-
tion of the PAVOUT voltage to the drain of the PA FET
when the PA is turned on. There are three settings in
the anshp[1:0] bits in the Conf0 register for the rate at
which the pulse ramps up: anshp[1:0] = 11 is the fastest
(approximately 1Fs); anshp[1:0] = 10 is approximately
1.5Fs and anshp[1:0] = 01 is approximately 3Fs; and
anshp[1:0] = 00 setting opens the connection between
PAOUT and PAVOUT, disabling the analog amplitude
shaping feature.
The internal variable shunt capacitor, which can be used
to match the PA to the antenna with changing transmitter
frequency, is controlled by setting the 5-bit cap vari-
able in the registers. This allows for 32 levels of shunt
capacitance control. Since the control of these 5 bits is
independent of the other settings, any capacitance value
can be chosen at any frequency, making it possible to
maintain maximum transmitter efficiency while moving
rapidly from one frequency to another. The internal tun-
ing capacitor adds 0 to 7.75pF to the PA output in 0.25pF
steps. The PA output capacitance at the minimum cap
setting is approximately 4.5pF.
ASK/FSK Transmitter
Analog Amplitude Shaping
Tuning Capacitor Settings
12.5µs
19