Electrical filter

Details Electrical filter Electrical filter

1987-04-21

1988-03-22

Nussbaum, Marvin L.

Wave transmission lines and networks

Coupling networks

Frequency domain filters utilizing only lumped parameters

333168, 333173, 330 9, 330109, H03H 7075, H03H 706, H03H 1112

Patent

active

047332050

ABSTRACT:
A continuous time electrical filter fabricated as an integrated circuit includes capacitors (CF,CN) and resistors (R1,R2). Since capacitors and resistors are difficult to integrate with accurately defined values, a trimming circuit is provided which operates switches (S1-SN) to select appropriate ones of the capacitors (CN) to accurately define the cut-off frequency of the filter. The trimming circuit comprises a capacitor (TC2) which is charged through a resistor TR1 during a first period and which is discharged in incremental steps by capacitor (TC1). The number of incremental steps is counted by a counter (11) and transferred to a register (13). The outputs (S1-SN) of the register (13) control the switches (S1-SN). Alternatively the values of the filter resistors may be adjusted, a convenient procedure being to short out selected portions of the resistors. More than one capacitor or resistor may be adjusted using a single counter and register. The trimming circuit also includes a switch (TS11) which connects the parasitic capacitance (CP1, CP2) of the capacitor (TC1) and an underlying conductive layer (22) and of a dummy resistor and the underlying layer (22) in parallel with the capacitor (TC1). The filter circuit is arranged so that the parasitic capacitance between the resistor (R1) and an underlying conductive layer and that between the capacitors (CF, CN) and the underlying conductive layer are connected in parallel with the fixed capacitor CF.

REFERENCES:
patent: 4114117 (1978-09-01), Ford

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