Biomedical Engineering Reference
In-Depth Information
Fig. 20 On-off keying
(OOK) modulating the
voltage-controlled oscillator
(VCO) at 1 kbps
Fig. 21 Transient response of
the two envelope detector
outputs when turning the
frequency-locked loop (FLL)
on and the envelope outputs
difference for settling time
characterization
the frequency distribution of the free-running VCO when the feedback loop is off
and when operating in locked mode. The mean center frequency is 59.34 GHz, with
a standard deviation of 195 MHz. Compared with the 503-MHz standard deviation
of the free-running VCO, the FLL provides an improvement in frequency variation,
while eliminating the need for an external reference and tracking the peak-efficiency
frequency of the integrated antenna.
Figure 20 shows the FLL Tx signal when the VCO is being OOK modulated at 1
kbps. The signal amplitude is small because it is down-converted through a passive
harmonic mixer which has an uncalibrated attenuation; therefore, this plot simply
verifies the OOK functionality. Figure 21 shows the two envelope detector output
signals when the FLL is OOK modulated and the difference of the two envelope
detector outputs as the error signal. The settling time is around 3
s once the loop is
turned on; therefore, the VCO can be powered on and FLL locked during every bit
transmission for data rates less than around 200 kbps. The measured results of the
FLL are summarized in Table 2 and compared with a state-of-the-art PLL, frequency
synthesizer, and OOK transmitter. While a frequency synthesizer requires a crystal
μ
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