WEBENCH^® Amplifier Designer

Inverting Amplifier

The Inverting Amplifier multiplies the input voltage by the desired negative gain:

Vout = -(Rf/Rg) x Vin

Note that with a single positive supply voltage, the input voltage must be negative, so that a positive output can be developed.

AC-Coupled Inverting Amplifier

The circuit multiplies the non-DC input voltage by the desired negative gain:

Vout = [-(Rf/Rg) x Vin(p-p)] + Vbias

Vbias is added to the noninverting input to bring that input voltage within normal amplifier operating range. It also provides an offset for the output, so it is within its operating range. Can also be used as a wide-bandwidth Bandpass Filter (20dB decade attenuation). For a narrow bandwidth filter, see the WEBENCH^® Active Filter Designer

Non-Inverting Amplifier

The Non-Inverting Amplifier multiplies the input voltage (Vin) by the desired positive gain, and subtracts a voltage proportional to the applied reference voltage: Vout = Vin x (1 + Rf/Rg) - Vref x (Rf/Rg) Note that if Vref = 0V, then the output voltage equation simplifies to:

Vout = Vin x ( 1 + Rf/Rg)

The feedback capacitor Cf rolls off the gain at frequencies above 1/2pi x RfCf, to attenuate high-frequency noise.

Low-Pass Filter

The Sallen-Key lowpass biquad filter is a classic design. This implementation has low sensitivity to changes in component values over process, environment, and time. Using the 2nd-order Chebyshev approach gives a relatively steep rolloff near the cutoff frequency fc. For more information on this design, see application note OA-27.

Low-Pass Filter 4th Order

This 4th order lowpass filter uses a Sallen-Key topology for each of the two 2nd order sections. The user can select the desired filter approximation. Using the Chebyshev approach gives a relatively steep rolloff near the cutoff frequency fc, while a Bessel response produces a smoother step response. The Butterworth response has a nearly-flat passband, with a high-frequency rolloff of 20dB/decade for every pole (4 in this case).

High-Pass Filter

The Sallen-Key highpass filter is a classic design. This implementation has low sensitivity to changes in component values over process, environment, and time. Using the 2nd-order Butterworth approach gives a straight-forward design with no peaking at the cutoff frequency fc. For more information on this design, see application note OA-29.

Active Filter

WEBENCH Active Filter Designer speeds the creation of advanced, highly customized filters. Filters may be specified by desired frequency response, or by a specific filter approximation and order. After the theoretical design is created, it is implemented using actual component values. The resulting filter can then be simulated.

Sensor Analog Front End (AFE)

For integrated LMP9xxxx Sensor AFE sensor circuit designs

Sensor AFE products are highly integrated, (re)configurable sensor interface ICs with an easy-to-use hardware/software development platform.

Sensor Path Design

For discrete (sensor + amplifier + ADC) circuit designs

The WEBENCH Sensor Designer tool provides a complete sensor to digital serial output solution, including sensor interface, excitation source, precision amplifier and filter, 8-bit through 16-bit ADCs, and a serialized output to connect to various back-end systems.

Integrator

The Integrator is used to calculate the integral of a signal. The output of the integrator is proportional to the area under the plot of voltage vs. time. For example, if the input signal is DC, then the output is a voltage ramp.

Because integration involves a known start time and end time, a reset circuit must be included to establish the start time before each integration time period. The integration end time occurs when the measurement is read.