DESIGN OF A 2.7-GHZ LINEAR OTA AND A 250-MHZ ELLIPTIC FILTER IN BIPOLAR TRANSISTOR-ARRAY TECHNOLOGY

The design of a tunable high-frequency fully differential bipolar operational transconductance amplifier (OTA) is presented. Techniques resulting in tunability and broadbanding are discussed, as well as unavoidable tradeoffs resulting from the lack of a vertical pnp device. Using an 8 GHz bipolar transistor array process, the simulated -3 dB frequency of the OTA is over 2.7 GHz, the maximum linear input range is +/-2.5 V, and the power dissipation is 28 mW for a power supply of +/-5 V. The OTA can also operate at a low power supply of +/-2.5 V. Applying the OTA as a building block, the design of a third-order elliptic OTA-C filter with cutoff frequency of 250 MHz and tuning range from 200 to 290 MHz is presented. Analysis of filter nonidealities, as well as predistortion and compensation techniques, are discussed. Detailed SPICE simulations verify the results of hand calculations and show that temperature variations from -30 to +100-degrees-C and supply variations from +/-4.5 to +/-7.5 V change the cutoff frequency of the filter by less than 10%. The Q-factor can be electronically adjusted for all frequencies in the tuning range.