# Definitions

## Table 1 - Definitions

Item Name | Description |
---|---|

Filter Type | The filter type can change how quickly the rolloff of the filter begins and whether it has ripples in the passband or stopband. FilterLab allows you to choose Butterworth, Chebychev, or Bessel for low-pass filters, and Butterworth or Chebychev for high-pass and band-pass filters. |

Topology | There are two available topologies to choose from, Multiple Feedback (MFB) and Sallen-Key (SK). MFB has inverting gain, while SK is non-inverting. Low-pass filters can be configured in MFB or SK. High-pass can only be configured in SK. Band-pass filters can only be configured in MFB. While, in general, it is possible to configure high-pass filters in MFB or band-pass filters in SK, these limitations are in place in FilterLab to optimize filter performance. The gain response of a Sallen-Key configuration has an upturn at very high frequencies. This is due to the op amp not being ideal and can be fixed either by adding another low-pass filter afterwards, by changing to the Multiple Feedback configuration, or by choosing a faster op amp. |

Passband Frequency (Hz) | The passband frequency for low-pass and high-pass is the frequency at the user-specified passband attenuation. All frequencies lower than the passband frequency (for low-pass) or higher than the passband frequency (for high-pass) will not be attenuated by more than the passband attenuation. Passband Center Frequency for Band-pass filters is the geometric mean of both frequencies at passband attenuation. |

Filter Order | Filter order refers to the degree or complexity of the filter's transfer function and the number of poles in the transfer function. The filter order indicates the slope of the filter's rolloff (-20dB*N/decade where N=order). FilterLab can support low-pass and high-pass filters between the orders of one and eight. Band-pass filters can be a 2^{nd}, 4^{th}, 6^{th}, or 8^{th} order. |

Filter Spec. Type | Analog filters are electronic circuits designed to process analog signals by allowing certain frequency components to pass through while attenuating or blocking others. These filters play a crucial role in various applications, including audio processing, signal conditioning, communications, and instrumentation. Analog filters are categorized based on their frequency response characteristics, and FilterLab supports low-pass, high-pass, band-pass filters. Low-pass filters pass (or allow) low frequencies through while attenuating higher frequencies. High-pass filters pass high-frequency signals while attenuating low frequencies. Band-pass filters are a combination of low-pass and high-pass filters, allowing only a certain range of frequencies and attenuating everything else. |

Voltage Ratio Gain V/V | Voltage Ratio Gain (V/V), often referred to simply as gain, is used to describe the amplification or attenuation of an input voltage signal by a specific factor. It indicates how much the output voltage of a circuit or device changes for a given change in the input voltage. Gain is commonly expressed in decibels (dB) or as a dimensionless ratio (V/V). |

Customize Filter Coefficients | This button enables the input of filter shape coefficients, which will be set per each stage in the Settings tab: Q - quality factor which determines the peaking of the magnitude response of the filter. FSF - frequency scaling factor which determines the passband or passband center frequency. Alpha - for band-pass filter calculations using Geffe’s algorithm. Beta - for band-pass filter calculations using Geffe's algorithm. |

Passband Attenuation | This is the desired passband attenuation (for Chebychev this is equivalent to the ripple). |

Approximation for Resistors | There are several standard resistor series commonly used in electronics, and each series follows a different pattern. The most widely used standard resistor series are E6, E12, E24, E96 and E192. Exact values are also available. |

Approximation for Capacitors | There are several standard capacitor series commonly used in electronics, and each series follows a different pattern. The most widely used standard resistor series are E6, E12, E24, E96 and E192. Exact values are also available. |

Op Amp Power Supply | You can choose either a single or dual power supply. |

Op Amp Type | By choosing Op Amp Type, you can select General Purpose, Precision, or All Op Amps. General Purpose op amps have an offset voltage of more than 1mV, while the Precision op amps have less than 1mV offset voltage. |

Choose My Own Op Amp | When Choose My Own Op Amp is enabled, you can select an op amp from the dropdown list to be used in the filter design. When Choose My Own Op Amp is disabled, the op amp dropdown will be disabled and FilterLab will choose the optimal op amp from the group specified in the Op Amp Type dropdown list. |

Group Delay | When Group Delay is selected, you can see the group delay response in the Filter Response tab. |

Input Impedance | When Input Impedance is selected, you can see the input impedance magnitude and phase response in the Filter Response tab. |

Step Response | When Step Response is selected, you can see the step response of the filter in the Filter Response tab. |

Noise Analysis | When Noise Analysis is selected, you can see the input noise voltage density plot in the Filter Response tab. |

Show previous plot | When this option is enabled, it will show the previous and current filter responses on the same plot. |

Plot amplitude as V/V | Enabling this will show the amplitude plot using volts over volts (V/V) instead of decibels (dB) on the Y-axis. |

Phase as radians | Enabling this feature will display the phase in radians instead of degrees. |

Auto Scale - Y | When Auto Scale - Y is selected, you can see full the Y-axis filter gain data in the “Filter Response” tab. Otherwise, the Y-axis will be constrained to [-140 dB, 20 dB]. |

Auto Scale - X | When Auto Scale - X is selected, you can see two decades before and two decades after the passband frequency. Minimum Observable Frequency and Maximum Observable Frequency will be hidden. When Auto Scale - X is unselected, Minimum Observable Frequency and Maximum Observable Frequency will be visible and enabled. |

Minimum Observable Frequency (Hz) | Minimum observable frequency represents the lower frequency limit displayed on the plot. This can be changed only if Auto Scale – X is disabled. |

Maximum Observable Frequency (Hz) | Maximum observable frequency represents the higher frequency limit displayed on the plot. This can be changed only if Auto Scale – X is disabled. |

Plot Variation (X-axis) | The Plot Variation allows you to change the X-Axis scale to be linear or logarithmic (Decade). |

GMIN | Resistors with values inverse to this value are added to the circuit to improve DC convergence. |

FSF Coefficient | FSF (Frequency Scaling Factor) determines the passband or passband center frequency. |

Q Coefficient | Q (Quality factor) determines the shape of the amplitude response of filter. |

Alpha Coefficient | Alpha is used for band-pass filter calculations using Geffe’s algorithm. |

Beta Coefficient | Beta is used for band-pass filter calculations using Geffe’s algorithm. |

Set capacitor | If the schematic contains capacitors that are too small or resistors that are too big, you can adjust the values using the Set capacitor option at each stage. |

Calculate | Use the Calculate button to implement any new changes and run the simulation. If the Calculate button is green, no new changes have been made. If the Calculate button is red, changes have been made but not yet implemented or simulated. |