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Active Filters

Active Filters

Active filters are electronic circuits that use operational amplifiers (op-amps), resistors, and capacitors to filter out unwanted frequency components from a signal. A first-order low-pass active filter is designed to pass signals with a frequency lower than a certain cutoff frequency and attenuate frequencies higher than that cutoff frequency. The transfer function for a first-order low-pass active filter is:

Passive Filters

Passive Filters

Passive filters are utilized to shape the frequency spectrum of signals across a diverse array of applications. These filters, using only passive elements like resistors (R), inductors (L), and capacitors (C), are capable of selectively allowing or blocking certain frequency ranges without the need for external power sources.
Low-Pass Filters
Low-pass filters are designed to transmit signals with frequencies lower than the cutoff frequency, ωc, and attenuate those above it. The cutoff frequency...

Bandpass Sampling

Bandpass Sampling

In signal processing, bandpass sampling is an effective technique for sampling signals that have most of their energy concentrated within a narrow frequency band. This type of signal is known as a bandpass signal. The key principle of bandpass sampling involves sampling the signal at a rate that is greater than twice the signal's bandwidth to prevent aliasing.
A bandpass signal has a spectrum with a lower frequency limit, denoted as ω1, and an upper frequency limit, denoted as ω2. The spectrum...

Repressible Operon: trp Operon

Repressible Operon: trp Operon

The trp operon in Escherichia coli exemplifies a repressible operon. It regulates the synthesis of tryptophan through repressor-mediated transcriptional control and attenuation. This dual regulatory mechanism ensures tryptophan biosynthesis occurs only when needed, conserving cellular resources.Structure of the trp OperonThe trp operon consists of five structural genes (trpE, trpD, trpC, trpB, and trpA) that encode enzymes for tryptophan biosynthesis. These genes are transcribed as a single...

Frequency Response of Op Amp Circuits

Frequency Response of Op Amp Circuits

Operational amplifiers (op-amp) are used in signal conditioning, filtering, or for performing mathematical operations such as addition, subtraction, integration, and differentiation. The frequency response of an op-amp is an important aspect that describes how the gain of the amplifier varies with frequency.
Frequency Response and Gain:
The gain of the op-amp, A(ω), is not a constant but a function of the input signal frequency. An op-amp can maintain a constant gain at low frequencies, known...

Design Example

Design Example

The innovation of touch-tone telephony revolutionized the telecommunications industry by replacing the traditional rotary dial with a dual-tone multi-frequency (DTMF) signaling system. This system uses a matrix-style keypad with buttons arranged in four rows and three columns, creating 12 distinct signals each assigned to a pair of frequencies. Each button press results in a simultaneous generation of two sinusoidal tones – one from a low-frequency group (697 to 941 Hz) and one from a...

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Related Experiment Video

Updated: Jun 22, 2026

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Published on: February 4, 2018

An externally tunable bacterial band-pass filter.

Takayuki Sohka¹, Richard A Heins, Ryan M Phelan

¹Departmentsof Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21212, USA.

Proceedings of the National Academy of Sciences of the United States of America

|June 9, 2009

Summary

Researchers engineered bacteria as a tunable filter for enzyme activity and molecules. This synthetic biology advance allows external control of biological systems, enhancing their versatility for biotechnology and research.

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Area of Science:

Synthetic biology
Biotechnology
Genetic engineering

Background:

Current synthetic biological systems require re-engineering of components for tuning.
Versatile biological systems can be tuned by external stimuli.

Purpose of the Study:

To engineer Escherichia coli cells as an externally tunable band-pass filter.
To develop a generalizable strategy for creating tunable biological systems.

Main Methods:

Engineered Escherichia coli with a genetic circuit.
Incorporated an enzyme-substrate pair as an attenuator within the genetic network.
Utilized external compound addition to modulate the band-pass filter's location.

Main Results:

Achieved external tunability of enzyme activity and small molecule filtering across 4 orders of magnitude.
Demonstrated bacteria growth patterning in response to chemical gradients.
Facilitated the isolation of engineered allosteric enzymes.

Conclusions:

The inclusion of an enzyme-substrate attenuator is a generalizable strategy for external tunability in biological systems.
This approach enhances the utility of synthetic biology for biotechnological applications.
The engineered system provides a tool for understanding natural biological design principles.