A Low Power Interference Robust IR-UWB Transceiver SoC for WBAN Applications - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 28

Fig. 4 Schematic of the ultra-wideband (UWB) transmitter
attained due to the positive feedback action of VCO and bandwidth boosting LC
components . By turning on the LC VCO only during the pulse generation, transmitter
with high energy efficiency can be designed and constant power efficiency can be
maintained across a wide range of data rate. Differential DA consists of NM 4 − 5 and
L 3 − 4 , they can further boost the output swing and also isolate the VCO core from the
external loading to reduce VCO pulling effect. NM 6 acts as a switch to enable/disable
DA, it is controlled by the TX enable signal (TX_EN) from digital baseband.
Low Noise Amplifier
A four-stage fully differential variable gain LNA is designed for the RX front-end.
Figure 5 shows the schematic of first two stages. Current reuse topology is utilized to
stack the two-stage cascaded amplifiers into one current-reuse cell. Hence, the power
consumption is reduced by half while the power gain is maintained. Same architecture
is used for the third and fourth stages without the input matching network. Similar
current reuse technique has been applied in single-ended LNA [ 12 ], however at least
four inductors are required in one current-reuse cell, excluding the input matching
circuit. Hence, a four-stage differential LNA will require eight inductors in total,
occupying a very large area. In this design, the symmetry of the differential LNA is
exploited and the single-ended inductors are replaced with differential inductors to
save chip area.