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 are 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 +or-2.5 V, and the power dissipation is 28 mW for a power supply of +or-5 V. The OTA can also operate at a +or-2.5 V. 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. Filter nonidealities are analyzed, and predistortion and compensation techniques, are discussed. Temperature variations from -30 to +100 degrees C and supply variations from +or-4.5 to +or-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.