Ultra-Wideband Imaging Systems for Breast Cancer Detection - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 89

V 3

C D M

V 6

V

V 1

V 2

V 2

V

C

OUT

V V 3

V

V 5

C BP

OUT

IN

V 4

V 1

V 5

C

V

V 4

V 6

D

M
ON-OFF KEYING (OOK)
MANCHESTER MODULATION
D IN

V

OUT

a b c

Fig. 9 a Ultra-wideband (UWB) transmitter circuit schematic diagram, b schematic of one current-
starved inverter, and c timing diagram of the UWB transmitter

position modulation (TH-PPM) or some other time-domain modulation schemes
which should be considered in the transmitter architecture. Also the correlator archi-
tecture is not always exactly similar to what was explained here, and it might vary
due to the needs of the specific system.

Design Example for Ultra-Wideband Transmitter

The circuit diagram of the all-digital pulsed UWB transmitter is shown in Fig. 9 .
The input data are modulated using on-off keying (OOK) Manchester modulation.
UWB pulses are generated on the rising edge of the modulated data (D M ). A delay
line bank is employed together with a capacitively coupled output combiner [ 21 ]as
shown in Fig. 9 a.
The modulated data are passed through a delay line and a delayed version of the
data is passed through three pulse generators. The pulse generators shape a first-
order Gaussian pulse at the rising edge of the input data. The presented digital UWB
transmitter achieves both power efficiency and spectral compliance in a much smaller
chip area compared to other designs [ 22 - 23 ]. As illustrated in Fig. 9 c, each pulse
generator forms pulses that are delayed, and have opposite signs. By capacitively
combining the three paths, the opposite signs are canceled, and the zero-DC double
differentiated Gaussian pulse propagates to the single-ended antenna. The width of
the output pulse depends on the delays in the delay line. The delay cells in all the
paths are implemented as current-starved inverters, shown in Fig. 9 b, to allow for
tuning of the UWB pulse width. The input Manchester-encoded data to the UWB
transmitter and its measured output UWB pulses are shown in Fig. 10 .
The UWB pulses are measured using custom-built UWB antennas (5 cm spac-
ing between the transmitter and receiver) and a custom-built receiver. A zoomed-in
version of one such measured UWB pulse overlayed on a simulated UWB pulse is