Analysis And Design Of Fourteenth Order Bandpass Filter

This dissertation introduced the working principle of the band-pass switched capacitor filter, and then gave the analysis of the non-ideal effects in the switched capacitor filter, designed the system architecture of band-pass filter composed of eighth order Chebyshev high-pass filter and sixth order elliptical low-pass filter. During the system design in Matlab, the structure, transfer function and coefficients of every order are designed. Based on the system level, the filter is realized in transistor level with full differential structure since the structure can eliminate the common mode noise to great extend and provide large output swing. After finishing every element in the filter, the whole circuit was simulated in Cadence. After finishing the layout of the filter post-simulation was also done. Finally the band-pass filter chip was tested and the result was analyzed.While analyzing the non-ideal effects in the filter, it was easy to find that the white noise introduced by the sampling switches because of its on-resistance could increase the noise in the pass band in the filter. The mismatch of capacitors could alter the transfer function of the whole system, and it may decrease the rate of stop-band attenuation and increase the ripple in the pass band. Finally, as the integrator is the fundamental element of the filter, the performance could greatly influence the characteristics of the filter. In the integrator the operational amplifier is non-ideal, and its gain, bandwidth, and slew rate are finite. Therefore it was inevitable to face the setting error in the integrator.During the system level design, in order to get high rate of stop-band attenuation, an eighth order Chebyshev high-pass filter and a sixth order elliptical low-pass filter were used to consist the band-pass filter. After finishing the whole transfer function of the filter, the coefficients of each order were seceded. The whole circuit was simulated in Cadence by csmc 0.5μm process. After simulating transistor-level the results show that the gain in pass band is about 93 dB, and the rate of stop-band attenuation is 78 dB every twice frequency. The layout of modulator is finished and the gain in pass band is about 93 dB during the post-simulation. Chip test result shows that when the pass band frequency is lower than 130 kHz, the pass band of the filter can be controlled by the two clocks which each control the high-pass filter and low-pass filter. The test results are as follows: the gain in the pass band is 85.6dB, the ripple in the pass band is 0.5dB, the noise in the pass band is1.3mVrms/Hz1/2 and the rate of stop-band attenuation is 74 dB every twice frequency.