Ultra-wideband (UWB) communication is expected to be used for many consumer electronics products in the near future. UWB systems are capable of supporting data rates as high as several hundred Mb/s while consuming a low power. Thus, they are suitable candidates for wireless personal area networks (WPANs). Although UWB systems are allowed to utilize the 3.1-10.6GHz band, first generation UWB systems will probably use the band below 5GHz. A 3.1-5GHz CMOS UWB transceiver is presented in this paper that is based on a direct sequence spread spectrum (DSSS) method as described in reference [1], and is different from 2 merged proposals called MB-OFDM and DS-UWB in the activity of the IEEE 802.15 TG3a [2]. Figure 11.8.1 shows a block diagram of the transceiver. The 8GHz VCO output is divided by 2 to provide 4GHz I and Q signals which are fed to the transmitter block (TX) and the receiver block (RX) as local oscillator (LO) signals, and to the high-speed current-mode logic circuits of the TX pulse modulator as a clock signal.The data, which is spread with a chip rate of 1Gchip/s in the baseband block, enters TX_I and TX_Q, and then the TX pulse modulator performs pulse shaping on each bit. Figure 11.8.2 shows the circuit schematic and simplified timing chart of the TX pulse modulator. The purpose of the pulse shaping is to lower the power density at 3.1GHz, to increase the total transmit power by flattening the spectrum of the transmit signal, and to pre-equalize the waveform of the transmit signal for the RX filter characteristic.In the context of this work, pre-equalization is to perform an approximate reversed-time matched filter of the RX filter as shown in Fig. 11.8.3.The TX pulse modulator in Fig. 11.8.2 allows programmable pulse shaping. The 1GHz Johnson counter has four 1GHz outputs, Q1-4, each shifted by 250ps. Each output is multiplied by a ±1 depending on the polarity of the phase amplitude contribution and the sense of the incoming data bit. The left most multiplier provides a DC offset to the pulse shape. TX_I and TX_Q waveforms are out of alignment with each other by 1ns to perform the π/2-shift BPSK modulation [1]. Outputs Q1-4 and the DC phase are transformed into currents proportional to the signal and the programmable values in the register. The currents are summed, and mixed with LO. The LO Mixer outputs I_OUT and Q_OUT are added up and the resultant signal has an almost constant envelope.The power amplifier has differential output ports whose impedance is 100Ω, and feeds the transmit signal to the antenna through an external balun. The maximum output power is -9dBm and can be set with eight 1dB steps. Figure 11.8.3 shows a measured spectrum of the transmit signal and an analysis result for modulation using a vector signal analyzer. The measured spectrum includes the frequency response of an external balun. The spectrum shows that the transmit signal, without an external band-pass filter, meets the FCC spectrum mask and spreads flat over a wide range centering on 4GHz, although it is slightly inclined. ...

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Motivating a child's interest in electrical engineering is challenging because the flow of electrical charge in most circuits is invisible and silent. In our approach we motivate learning through creation of reliable, robust, state-of-the-art solar rechargeable reading lights for delivery to younger children in the developing world through existing research and philanthropy networks. To engage students, we focus on the conservation of energy principle and concepts of voltage-chargeenergy, facilitating high-level theory-of-operation comprehension while limiting new terminology needed.Based on student feedback in a pilot project, the altruistic aspect of our "LearnBuild-Test-Share" approach significantly motivated enrollment, with girls comprising 47% of the participants.