# A Low Cost BLE Transceiver with RX Matching Network Reusing PA Load Inductor for WSNs Applications
## 4 Measurement Results and Discussion  
The BLE transceiver is implemented in a standard 110 nm CMOS technology using a single-poly and six-metal layers (one thick copper and one thick aluminum layer). The chip microphotograph is shown in Figure 12. Only two inductors, one for front-end and one for VCO, were implemented. The die area is 3.6 mm\({}^{2}\), in which the front-end circuits only occupies 0.24 mm\({}^{2}\), while the rest is PLL, analog baseband, digital modular, demodulator and digital signal processing. Without using off-chip TRX-switch and Balun, this transceiver achieves small area and high-level integration. Figure 11: Simplified schematic of VCO. Figure 12: Chip micrograph of the proposed BLE transceiver. Figure 13: (**a**) Measured TX impedance in SMITH chart; (**b**) Measured RX impedance in SMITH chart from 2.4 GHz to 2.5 GHz. Figure 13 shows the S\({}_{11}\) of the RX and TX. Both TX and RX achieve S\({}_{11}\) less than 10 dB over the entire operating band. This verifies the effectiveness of the proposed TRX-switch and matching network combination scheme. The discrepancy between the measured S\({}_{11}\) and simulated S\({}_{11}\) (shown in Figures 4 and 6) might result from the inaccurate modeling from both inductor and the parasitic components of PCB and bonding wire. The noise performance of the RX has been evaluated from the antenna port to the ADC outputs. Figure 14 shows the measured RX performance. The NF of the RX shown in Figure 14a achieves 6-7 dB within the ISM band. Therefore, the sensitivity for the BLE Standard calculated from (1) is about \(-93\) dBm, which is much higher than the BLE specification requirements (\(-70\) dBm). The total current consumption of RX is 9.7 mW, and the power loss breakdown of RX is shown in Figure 14b. Among the RX power losses, the ADC and complex filter consume 2.4 and 1.4 mW, respectively, which are mainly from their operational amplifiers. LNA consumes 1 mW, 70% of which is from the first stage, while the buffer contributes the remaining 30%. The mixer consumes less than 0.5 mW which is mainly from the core circuits. 1 mW is consumed by BBPLL, 40% of which is from the ring oscillator, 20% from PFD, 20% from CP, the rest from divider. RFPLL consume about 2.1 mW of power, with its VCO, PFD, CP and prescalar consuming 1 mW, 0.2 mW, 0.2 mW and 0.6 mW, respectively. Figure 14: (**a**) Measured NF in ISM band; (**b**) RX power loss breakdown; (**c**) Measured the third-order intermodulation product; (**d**) Measured the two-order intermodulation product. For the linearity performance, the measured 1 dB compression point (P1 dB) of the receiver is about \(-29\) dBm. Additionally, Figure 14c,d show the 3 rd and 2 nd intermodulation products. Two interfering sine wave signals (listed in Table 1) are input to the receiver with a channel gain G\({}_{\text{C}}\) = 74 dB, and IIP\({}_{\text{3}}\) = \(\text{P}_{\text{in}}\) + \(\text{(P}_{\text{in}}\) + \(\text{G}_{\text{C}}-\text{P}_{\text{O3}})/2\), while IIP\({}_{\text{2}}\) = \(2\text{P}_{\text{in}}\) - \(\text{P}_{\text{O2}}\) + \(\text{G}_{\text{C}}\). The measured IIP\({}_{\text{3}}\) and IIP\({}_{\text{2}}\) are thus \(-17.1\) dBm and \(9.8\) dBm. The IIP\({}_{\text{2}}\) performance might result from the following factors: (1) The single-ended LNA used in this work does not suppress the even-order harmonic distortion; (2) The input of down-mixer is not exactly symmetrical, as shown in Figure 8, which causes the even-order harmonic rejection not as good as a fully differential topology. But the IIP\({}_{\text{2}}\) performance of this work still meets the intermodulation requirement in BLE standard [4]. For the more severe cases not defined in [4], such as that with a large modulated out-of-band interference, a SAW filter might be needed for this work. Figure 15a shows that the TX output power variations are less than 1 dB within the 2.4 GHz ISM band. The TX current consumption for various output powers is plotted in Figure 15b.