Biomedical Engineering Reference
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Fig. 9 a An injection-locked transmitter. b Transient output of the transmitter
frequency-locked to the reference oscillator, and it provides a larger output power to
the antenna. The reference oscillator and the power oscillator can be modulated by the
baseband data with FSK or OOK modulation. Figure 9 b shows the transient output
of the transmitter as response to the baseband data with OOK modulation scheme
[ 12 ]. The rectangular envelope at the output of the transmitter, however, does not
meet the IEEE 802.11.15.4a spectrum mask requirements. On the other hand, if
the reference oscillator is modulated by the shaped pulse as defined in 15.4a, weak
injection locking would be an issue during the ramping up time of the modulated
signal. For this reason, the scheme in Fig. 9 a doesn't fit the requirement of our
system.
In this work, we present an injection locked transmitter with pulse shaping func-
tions as shown in Fig. 10 . The baseband data is pulse-shaped and modulates the
power oscillator. In this way, the output envelope of the transmitter follows the pulse
shape of the baseband data, and meets the spectrum mask requirements. The refer-
ence oscillator is not modulated and the output keeps a constant amplitude, which
ensures the injection between the reference and the power oscillator. The power os-
cillator can be modulated by the baseband data with FSK, OOK, PSK, PPM, etc. As
compared to the previous architecture, the injection-locked transmitter can achieve
larger output power and higher power efficiency at high frequencies (i.e., 10 GHz).
The entire transmitter including the digital baseband is integrated into a single-
chip TX-IC. The digital baseband generates data signals for a standard compliant
frame; i.e., pre-amble and payload, as well as the control data to duty cycle the
front-end blocks. The digital data is converted to pulses by a pulse shaper, which
modulates the power oscillator. The local oscillator generates the carrier frequency
between 6 and 10 GHz and locks the power.
The schematic of the pulse shaper and the power oscillator are also shown in
Fig. 10 . In the pulse shaping circuit, the digital baseband data B1P/N is converted to
a differential pair of analog signal IF
/- with RC pulse shape. The RC time controls
the shape of the pulse and is a trade-off between output power and the 15.4a spectral
mask compliancy.
In the power oscillator, transistor M7/8 and the LC tank form a tunable LC-tank
oscillator, which can be locked to the injected LO
+
+
/- signal from 6 to 9 GHz in
measurements. The LO signals (LO
/-) are fed to the power oscillator by transis-
tors M6/M10 and M5/M9 depending on the IF
+
+
/- signal on M1-M4. The phase
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