Design Of CMOS 4^th-order Gm-c Low-Pass Filter With Wide Tuning Range In High Frequency

In any system that interfaces with the real world, the quantity to be measured and later processed is always contaminated with noise and interferes. A filter is usually used in order to get rid of the unwanted noise and reject the surrounding interferes. Integrated analog filters have been used broadly. Integrated analog filters can be categorized into two categories:discrete-time filters and continuous-time filters (CTF). The CTF have anti-aliasing, preconditioning, smoothing and reconstruction functions. At high frequencies, CTF perform the entire signal processing in analog domain to realize magnitude or phase shaping.Gm-C filters are one kind of CTF. The Gm-C filter has better frequency response than the other kinds of CTF due to their open loop configuration. In high frequency the Gm-C filter has wide range of applications for example in medical, digital radio receiver, Bluetooth receiver, hard disk driver and LC oscillator and radio frequency wireless communication etc. Furthermore the unavoidable tuning scheme must be adopted to compensate the Gm and C deviations due to process technology variations. The cut-off frequency can be tuned either by changing the value of Gm and/or the capacitance.A 4th-order Gm-C low pass filter with an automatic tuning system is discussed and implemented in this paper. Nauta's OTA is used to achieve high performance in linearity and power consumption. Tuning circuit is used to compensate process technology variations.Biquad circuit is adopted because of its advantages in design and layout. The value of gm is maintained constant and the value of load capacitance is changed to alter the cutoff frequency in this work. The filter is implemented in CMOS 0.5μm Double Poly Triple Metal Mixed Signal Process and 3.3V power supply is adopted. The layout area is 330μm*140μm.The circuit consumes 4.3mA through a 3.3V power supply with a corner frequency tunable range from 15MHz to 95MHz in post layout simulation. The THD is about -54dB when input voltage is 0.2Vpp. The input noise is less than 43 nV/(?).