An experimental filter was designed to operate at 3.6 GHz using mainstream
0.18 μm CMOS. In the design, the Q-enhancement technique was used to overcome the low-Q characteristics of the CMOS on-chip inductors. A sixth-order bandpass filter
with a wide passband and a high image rejection was built by cascading three stages
of second-order Q-enhanced filters. A combination of three biquads with offset in center
frequency provides wider tuning frequency and bandwidth. This high-performance filter
provides a 340 MHz tunable center frequency around 3.6 GHz, an image
rejection of 50 dB and a tunable Q from 25 to 50 for a bandwidth adjustment from 95 MHz to 35
MHz. The filter achieves an
18 dB voltage gain while consuming 130 mW of power at
1.8 V DC supply. The chip occupies an area of 900×900μm2 including all the required bonding pads. The design provides a simple
architecture to simplify tuning scheme for both frequency and bandwidth for practical use.
The tunable ability of the design could be exploited in further study to be used as
a channel-select filter in the gigahertz range.
100MHz, 6th Order, Leap-Frog gm-C High Q Bandpass Filter and On-Chip Tuning Scheme