# Sub-Milliwatt Transceiver IC for Transcutaneous Communication of an Intracortical Visual Prosthesis
## 5 Results
### IR-UWB Transmitter  
#### 5.1.1 IC Measurement Results  
Figure 12 shows more transmitter output (bottom panel) on a bitstream and shows the input 50 Mbps data stream from the Analog Discovery 2 acting as a pattern generator (top panel). The measured transmitted bits appear to be distorted due to the bandwidth limitation of the pattern generator and also due to the distortion at the interface when the input bit signal is tapped into the oscilloscope, which does not influence performance. A '1' logic level corresponds to no pulse on the output, while a '0' logic level corresponds to a pulse at the output. This demonstrates the on-off keying modulation. Although not depicted, the output voltage levels of the measured and simulated signals agree.  
Figure 13 shows the spectrum (FFT of the time signal) of the transmitter output and also with and external bandpass filter for the 3-5 GHz band. To show the additional effect of a bandpass filter, the VBFZ-3590-S+ from Mini-circuits USA, which is a bulky off-chip BPF, is included in a measurement. The measured output spectrum falls below the FCC spectral mask limits. The transmitter waveform will further meet the IR-UWB standard in a full system scenario due to the skin attenuation.  
Figure 14 shows the measured power consumption of the transmitter versus supply voltage. This is not the optimized result yet, and is not able to be able to compared with the post-layout simulation. A 1 k\(\Omega\) resistance from a potentiometer in series with the supply voltage was used to generate current for the oscillator's current control. Another 1 k\(\Omega\) resistance from a potentiometer in series with the supply voltage was used to generate current for the impulse generator's current control. The measured and simulated power consumption agree well and show the same trend. Figure 15 shows the corresponding simulated RF output power versus voltage supply for the unoptimized IR-UWB Transmitter  
Figure 12: Measured time domain waveform of the IR-UWB transmitter at 50 Mbps bitstream, 1.3 V supply voltage. The top panel shows the input bitstream. The bottom panel shows the output of the transmitter IC, which is the modulated data. The measurement has been done without antennas for the sake of convenience.  
at 50 Mbps data rate vs supply voltage, with fixed 1 k\(\Omega\) resistance for current control. Another purpose of Figure 14 is to show how the power consumption scales with the supply voltage to emphasise the predominantly digital architecture. This gives a promise for even better performance with more advanced CMOS technologies, operating operates at lower power supply voltages. The results in Figure 14 are for comparison only and are not optimized yet. The optimization was done as shown below.  
The current from both current supplies (to control the oscillator and pulse generator) were adjusted to find optimal pulses per bit and power-output level. At 1.3 V supply voltage, using 100 uA and 10 uA for impulse generator and oscillator control respectively, the transmitter consumed 0.15-0.3 mW. The output waveform for this setting, already shown in Figure 12, has an RMS output power at the transmitter of \(-\)27 dBm. The simulated power breakdown of the transmitter is as follows: 75% is consumed in the pulse generator, 20% in the oscillator, and 5% in the modulator.  
Figure 14: Power-consumption versus voltage supply for the unoptimized IR-UWB Transmitter at 50 Mbps data rate with fixed 1 k\(\Omega\) resistance for current control.  
Figure 13: Spectrum of the IR-UWB transmitter before and after bandpass filter at 1.3 V supply voltage. The FCC spectral mask is also shown. The spectrum is computed in the oscilloscope as the FFT of the measured time signal.