# A Low Cost BLE Transceiver with RX Matching Network Reusing PA Load Inductor for WSNs Applications
## 4 Measurement Results and Discussion
It consumes 9.4, 8.4 and 7.9 mW at output powers of 0, \(-3\) and \(-10\) dBm, respectively. Figure 16a shows the measured eye diagram and spectrum of BLE modulation (BT = 0.5), and Figure 16b gives the in-band spurious emission performance, which is far less than the requirement in the dashed lines. The measured FSK error of BLE is 2.97% as shown in Figure 16c. All the measured modulations meet the accuracy specifications with decent margins. The power loss breakdown of TX with 0 dBm output is shown in Figure 16d. Most of the power loss is from PA, which is 5.8 mW. The last stage of the PA contributes more than 80% of this power consumption. On the other hand, the power loss on the PLL, XO and divider-by-2 circuit are similar to those in the receiver. The PA efficiency is not as high as the state-of-art works due to the following two reasons: (1) The cascade stage of PA (NM\({}_{\text{3}}\)) employs thick gate oxide to ensure the reliability of PA. However, the on-resistance and parasitic capacitance of thick gate oxide FET are larger than the thin gate oxide FET. Therefore, more power is consumed, comparing to the scheme using thin gate oxide FET; (2) This work employed an 110 nm CMOS process. With much larger parasitic capacitance, the switching loss is larger for this design. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Test Mode** & \(f_{1}\) **(MHz)** & \(f_{2}\) **(MHz)** & **LO (MHz)** & \(\text{P}_{\text{in}}\) **(dBm)** & **Gain (dB)** & **Measured** & **Results** \\ \hline IIP\({}_{\text{3}}\) & 2048.2 & 2051.1 & 2045 & \(-50\) & 74 & \(\text{P}_{\text{O3}}\) = \(-41.8\) dBm & IIP\({}_{\text{3}}\) = \(-17.1\) dBm \\ IIP\({}_{\text{2}}\) & 2048.5 & 2048.2 & 2045 & \(-50\) & 74 & \(\text{P}_{\text{O2}}\) = \(-35.8\) dBm & IIP\({}_{\text{2}}\) = \(9.8\) dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: IIP\({}_{\text{3}}\) and IIP\({}_{\text{2}}\) measurement conditions and results. Figure 15: (**a**) Measured Pout variation VS ISM band frequency; (**b**) Measured power consumption vs. output power. The measured output spectrum is presented in Figure 17, with 0 dBm required signal and \(-34.82\) dBm 2 nd harmonic emission, which meets the specification of the European standard [36] Considering the out-of-band spurious emission requirements are different in the intended countries of sales [4], more severe requirements in other standards might be employed for some specific applications. In this scenario, this design should further reject the 2 nd harmonic by using a SAW filter, or reducing the output power. Figure 16: Measured TX performance. (**a**) Measured eye diagram of BLE (BT = 0.5); (**b**) Measured spectrum of BLE; (**c**) Measured FSK Error; (**d**) Power consumption summary at 0 dBm output power. Figure 17: The measured output spectrum with 0 dBm required signal and \(-34.82\) dBm 2 nd harmonic spurious emission. The PLL phase noise is measured at the VCO output and the result is ploted in Figure 18a. At 4.8 GHz, the phase noises at 10 kHz, 1 MHz and 3 MHz offsets are \(-83\) dBc/Hz, \(-108\) dBc/Hz and \(-114\) dBc/Hz, respectively. When applied to the LO port, the phase noise will be reduced by 6 dB due to the VCO frequency divided by 2. Therefore, the phase noise in this work is far lower than the BLE system requirements. As shown in Figure 18b, the measured PLL lock time is faster than 33 \(\upmu\)s.  
The performance of the proposed transceiver is summarized and compared with some state-of-the-art designs in Table 2. Due to the proposed front-end, only two inductors were employed in this work, and a minimum front-end silicon area is achieved. Furthermore, the TRX-switch and matching network are integrated in this work. By optimizing the impedance and matching network, and choosing a single-ended architecture for both LNA and PA, comparable S\({}_{11}\), NF, output power and linearity are achieved with this proposed design. These verify the effectiveness and applicability of the proposed BLE transceiver for WSNs applications.