Title:
FILTER
Document Type and Number:
Japanese Patent JPS63191408
Kind Code:
A
Abstract:
A filter comprises an amplifier circuit arrangement having a signal input (1) and a signal output (8) and a coupling (36) between a point (37) on a signal path (39) to the signal input and a point (38) on a signal path from the signal output. The amplifier circuit arrangement comprises an inverting amplifier (6) to the input (5) of which the signal an input (1) is connected via a series impedance (7), e.g. a resistor. A feedback impedance (9), e.g. a capacitor, connects the amplifier output (8) to its input (5) so that this input constitutes a virtual earth. The phase relationship between the input and output signals of such an arrangement changes from inverting to non-inverting at frequencies at which the gain of the amplifier drops to below unity, because of forward feed through the feedback impedance (9), thereby upsetting the phase relationship between the signals passing through the arrangement and those passing through the coupling. Accordingly a further impedance (10), e.g. a capacitance, is provided between the common point (11) of the series and feedback impedances and ground. At frequencies at which the amplifier gain is high this has virtually no effect, because of the virtual earth existing at the common point (11). However, at frequencies at which the amplifier gain drops to unity or below the virtual earth effect is lost and the further impedance forms a potential divider with the series impedance (7), reducing the proportion of the input signal which can take the direct forward path through the feedback impedance.
Inventors:
POORU ANTONII MOOA
KORIN RISURII PERII
KORIN RISURII PERII
Application Number:
JP30603087A
Publication Date:
August 08, 1988
Filing Date:
December 04, 1987
Export Citation:
Assignee:
PHILIPS NV
International Classes:
H03H11/12; H03H19/00; (IPC1-7): H03H11/12
Attorney, Agent or Firm:
Akihide Sugimura (1 outside)