Fail-safe active band-pass filter
First Claim
1. A fail-safe electronic filter for passing a signal having a preselected frequency comprising, an amplifier having an input and an output circuit, a feedback path including an R-C twin-T network connected from said output circuit to said input circuit of said amplifier, an isolation circuit connected between said output circuit of said amplifier and said R-C twin-T network to prevent an increase in the gain of said amplifier due to an increase of resistance in said R-C twin-T network, said R-C twin-T network is imperfectly nulled to provide regeneration at said preselected frequency and to provide degeneration at all other frequencies from said output circuit to said input circuit of said amplifier so that an output signal is only available on an output terminal during the presence of said preselected frequency signal at said input circuit of said amplifier and in the absence of a critical component or circuit failure in the fail-safe electronic filter.
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Accused Products
Abstract
This disclosure relates to an improved fail-safe electronic filter circuit including a common-emitter transistor amplifier having a feedback path. The feedback path includes an R-C twin-T network which is imperfectly nulled to only provide regeneration at a preselected frequency. An emitter-follower circuit operates to isolate the series resistance branch of the R-C twin-T network from the collector of the transistor amplifier so that an output signal is only available during the presence of a signal having the preselected frequency and in the absence of a critical component or circuit failure.
9 Citations
8 Claims
- 1. A fail-safe electronic filter for passing a signal having a preselected frequency comprising, an amplifier having an input and an output circuit, a feedback path including an R-C twin-T network connected from said output circuit to said input circuit of said amplifier, an isolation circuit connected between said output circuit of said amplifier and said R-C twin-T network to prevent an increase in the gain of said amplifier due to an increase of resistance in said R-C twin-T network, said R-C twin-T network is imperfectly nulled to provide regeneration at said preselected frequency and to provide degeneration at all other frequencies from said output circuit to said input circuit of said amplifier so that an output signal is only available on an output terminal during the presence of said preselected frequency signal at said input circuit of said amplifier and in the absence of a critical component or circuit failure in the fail-safe electronic filter.
Specification