# A Novel Active Polyphase Filter Employing Frequency-Dependent Image Rejection Enhancement Technique
## 5 Comparative Analysis of Simulation and Measurement Results  
Table 1 demonstrates the comparison of the simulated and measured results of each performance of the proposed single-stage APPF. Among them, the simulation and measurement results for the performance of power consumption, area, OIP3, gain, and IRN are in general agreement. Errors in power consumption, area, gain, and IRN are mainly composed of accuracy errors in the simulation model and random errors in the actual test. The OIP3 simulation object only includes the proposed APPF, while the OIP3 test is the output of the whole channel including the LNA, mixer, single-stage APPF, and buffer. The LNA and mixer combination before the APPF has a gain of about 40 dB on the signal, so there is a 40 dB difference in input signal power between the OIP3 simulation and measurement results. The buffer circuit with high linearity after the APPF is a gain approximately equal to 0 dB, so the overall channel circuit linearity is basically determined only by the single-stage APPF. Therefore, the simulation and measurement results of OIP3 are basically the same. The IRR measurement results show a certain degree of degradation compared to the simulation results. Specifically, the optimal IRR is degraded by 6.7 dB, and the IRR at 10 MHz operating bandwidth is degraded by 0.7 dB. The possible causes of degradation include the following. The first is the control accuracy of the compensation current. In the simulation, the compensation current can be adjusted to the optimal value so as to obtain the optimum IRR, while in the chip, the compensation current is controlled by the serial peripheral interface (SPI), and the resolution of the compensation current value is limited. The second is a slight I/Q channel amplitude and phase imbalances that may exist in the chip, caused by random errors in the I/Q channel devices during production. The third is that the quadrature LO signals generated by the PLL may be less than perfect, with some amplitude and phase imbalances. The proposed design can handle the phase \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Result**} & **Optimum** & **IRR (dB) @ Band-Width** & **Power** & **Area** & **OIP3** & **Gain** & **IRN** \\  & **IRR (dB)** & **\textgreater{} 10 MHz** & **(mW)** & **(mm2)** & **(dBm)** & **(dB)** & **(\#V)** \\ \hline Simulation & 63.7 & 31.7 & 1.48 & 0.051 & 0.94 & 3.75 & 34.5 \\ Measurement & 57 & 31 & 1.5 & 0.051 & 0.9 & 3.53 & 37.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance comparison between simulation and measurement results. Figure 19: Measured OIP3 at the output of the proposed single-stage APPF. imbalance of the signals input to the APPF well, and the possible amplitude imbalance in the signals will make the IRR slightly degraded. Although the IRR measurement results of the single-stage APPF are negatively impacted by the above factors, it still has an excellent image rejection effect. In summary, the measurement results are slightly degraded compared to the simulation results, but the differences are within the acceptable normal range. The measurement results strongly support the effectiveness of the proposed technique and prove the application value of the proposed design. The overall performance of the proposed design is compared with [13; 17; 18; 21; 24], as shown in Table 2. In low-IF receivers, image rejection filter schemes realized after down-conversion include the complex filter schemes RC-PPF, Active-RC, CBPF, and APPF. IRR is the core performance parameter of the image rejection filter because the rejection capability is measured by it. Image rejection filters can be cascaded in multiple stages to improve the IRR. Therefore, IRR per stage, a parameter defined as the total IRR divided by the number of stages, is listed to more objectively compare the image rejection capabilities of different designs.