Low- Pass Filter

10Hz Active Low-Pass Filter

This “10Hz Active Low-Pass Filter” circuit offers a very low frequency cutoff and it has the ability to operate on single supply voltages. As shown, this is a second- order unity- gain Butterworth low- pass filter using a Sallen- Key topology. One advantage of a Sallen- Key LPF over one configured as a Multiple Feedback LPF is that it is non-inverting–therefore an input signal with a positive DC offset can be accomodated. A low input bias current op amp is required for a very low frequency low- pass filter as the R values are necessarily high. Thermal noise contributed by these resistors, however, can be reduced by reducing their values by an order of magnitude together with increasing the capacitor values by an order of magnitude. Resistor thermal noise will thereby be decreased by the square- root of 10.  (Circuit is created by Neil P. Albaugh,  TI – Tucson )

10Hz Active Low-Pass Filter circuit:

Active low-pass filter-blog

 

Online Simulation of the “10Hz Active Low-Pass Filter” Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud and analyze the circuit, or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

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Low-Pass Filter With Very Low DC Offset

This filter’s unusually low DC offset is due to the use of an OPA380 at U1. While this amplifier is usually employed as a transimpedance amplifier, it can also be used as an inverting op amp. In this configuration it provides wide bandwidth with extremely low input offset voltage and drift.

The OPA380 is a monolithic 85MHz GBW CMOS op amp with an internal auto- zeroed integrator. This integrator forces the high-speed op amp input offset and drift to virtually zero.

This 100kHz “Low-Pass Filter With Very Low DC Offset” circuit is a two- pole multiple- feedback filter with a Butterworth response. This filter has a DC gain of 1V/V or 0dB. Above the  -3dB corner frequency its response is close to theoretical up to 10MHz; above this frequency the finite GBW of U1 prevents much additional filter rolloff. An OPA380 is not suitable for a Sallen- Key active filter; that topology requires an op amp to be used as a non-inverting amplifier. The OPA380’s non-inverting input is a very low bandwidth integrator input. (Circuit is created by Neil P. Albaugh, TI – Tucson )

“Low-Pass Filter With Very Low DC Offset” Circuit:

LPF with very low DC offset-blog

Online Simulation of the “Low- Pass Filter With Very Low DC Offset” Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud and analyze the circuit, or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

Share and Enjoy

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