Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Patent
1994-01-14
1995-05-02
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
330306, 330277, H03B 104
Patent
active
054123356
ABSTRACT:
A filter (62) receives an input current signal and provides a filtered output signal in response. The filter (62) presents an extremely low-impedance input node (72) to the source of the input current signal, such as a current digital-to-analog converter (DAC) (62), thus avoiding modulating the input current signal. The filter (62) includes a virtual ground circuit (70) connected to the input node (72) followed by a filter (80) such as a biquad filter. The virtual ground circuit (70) has a high-gain cascoded loop to provide an intermediate current at a high-impedance output terminal (82), which is connected to an input terminal of the filter (80). The virtual ground circuit (70) is implemented without operational amplifiers and resistors, thus providing high linearity without a large amount of integrated circuit area.
REFERENCES:
patent: 3107331 (1963-10-01), Barditch et al.
patent: 3549910 (1970-12-01), Ogawa et al.
patent: 4555623 (1985-11-01), Bridgewater et al.
patent: 4728905 (1988-03-01), Zhiwei
patent: 4767946 (1988-08-01), Taylor
Serge Ramet; "A Low-Distortion Anti-Aliasing/Smoothing Filter for Sampled Data Intergrated Circuits," Reprinted from IEEE J. Solid-St. Circuits; vol. SC-23, No. 5, pp. 343-346 (1988).
Jackson H. Spence
May Marcus W.
Callahan Timothy P.
Motorola Inc.
Polansky Paul J.
Shin Eunja
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