Fully differential non-op-amp-based positive feedback BJT biquad

Details Fully differential non-op-amp-based positive feedback BJT biquad Fully differential non-op-amp-based positive feedback BJT biquad

1993-10-01

1995-05-23

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330306, H03F 345, H03F 3191

Patent

active

054184924

ABSTRACT:
The present invention comprises a fully differential non-op-amp based BJT biquad filter. The biquad filter comprises an unity gain follower receiving a positive and a negative differential input signals for generating a positive and a negative differential output signals. The biquad filter further includes a first positive feedback line connecting the positive output signal to the positive input signal and a second positive feedback line connecting the negative output signal to the negative input signal. The first positive feedback line includes a first capacitor connected in series therein and the second positive feedback line includes a second capacitor connected in series therein wherein the first and the second capacitors are of substantially equal capacitance. The unity gain follower further comprises a plurality of bipolar NPN devices and resistors connected between a common higher DC voltage and a common lower DC voltage through a constant DC current emitter. The unity gain follower is a fully differential follower which further comprises an input voltage shifting stage for receiving and shifting the voltage level of the positive and negative input signals. The unity gain follower further includes a transconductance stage for converting the shifted voltages from the input voltage shifting stage to a positive and a negative current outputs. The unity gain follower further includes a cascode stage for receiving and processing the positive and negative current outputs responsive to the bandwidth of the current outputs to generate a positive and a negative cascoded current outputs. The unity gain follower further has a load stage for receiving the cascoded current outputs to generated a positive and a negative loading voltages. The unity gain follower further includes an output voltage shifting stage for receiving and shifting the loading voltages to generate a positive and a negative shifted output voltages. The unity gain follower further includes an output buffer stage for receiving the shifted output voltages from the output voltage shifting stage and generate a positive and a negative output voltages to provide a low output impedance to the biquad filter.

REFERENCES:
patent: 5105163 (1992-04-01), Voorman
patent: 5117199 (1992-05-01), Wang et al.
patent: 5218319 (1993-06-01), Takimoto

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