This circuit inverts the input
signal, Vi, and applies a signal gain of –40dB. The common-mode voltage
of an inverting amplifier is equal to the voltage applied to the non-inverting
input, which is ground in this design.
- The common-mode voltage in this
circuit does not vary with input voltage.
- The input impedance is
determined by the input resistor. Make sure this value is large when
compared to the output impedance of the source.
- Using high-value resistors can
degrade the phase margin of the circuit and introduce additional noise in
the circuit. The capacitor in parallel with R2
provides filtering and improves stability of the circuit if high-value
resistors are used for both the input and feedback resistances.
- Avoid placing capacitive loads
directly on the output of the amplifier to minimize stability issues.
- Small-signal bandwidth is
determined by the noise gain (or non-inverting gain) and op amp
gain-bandwidth product (GBP).
- Large signal performance may be
limited by slew rate. Therefore, check the maximum output swing versus
frequency plot in the data sheet to minimize slew-induced distortion.
- For more information on op amp
linear operating region, stability, slew-induced distortion, capacitive load
drive, driving ADCs, and bandwidth see the Design References section.
- Note that higher input voltage
levels may require the use of multiple resistors in series to help reduce
the voltage drop across the individual resistors. For more information, see
the Design References section.
The transfer function of this
- Calculate the gain required for the
- Choose the starting value of
- Calculate for a desired signal
attenuation of 0.01 V/V.
- Select the feedback capacitor, C1, to
meet the circuit bandwidth.
- Calculate the minimum slew rate
required to minimize slew-induced distortion.
- SRLMV861 =
18V/µs; therefore, it meets this requirement.
- Calculate the circuit bandwidth to ensure it meets
the 1-MHz requirement. Be sure to use the noise gain, NG, or non-inverting gain,
of the circuit.
- BWLMV861 = 30MHz; therefore, it meets this requirement.
- If C1 is not used to
limit the circuit bandwidth, to avoid stability issues ensure that the zero
created by the gain setting resistors and input capacitance of the device is
greater than the bandwidth of the circuit.
- Ccm and
Cdiff are the common-mode and differential input
capacitance of the LMV861, respectively.
DC Simulation Results
AC Simulation Results
Transient Simulation Results
400-Vpp input sine wave yields a 4-Vpp output sine wave.
- See Analog Engineer's Circuit Cookbooks for
the comprehensive TI circuit library.
- SPICE Simulation File SBOC522.
- TI Precision Labs
- For more information on
circuits with larger input voltages, see Considerations for High-Voltage
Design Featured Op
0.1V) to (Vcc – 1.1V)|
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