1. Field
Embodiments of the invention relate to electronic devices, and more particularly, to notch filters.
2. Description of the Related Technology
An amplifier, such as an operational amplifier, can include chopper circuitry and a notch filter to help reduce the amplifier's input offset voltage. For example, the amplifier can include a first chopping circuit used to periodically swap or chop the positive and negative inputs of the amplifier's input stage at a chopping frequency and a second chopping circuit used to periodically swap or chop the positive and negative outputs of the amplifier's input stage at the chopping frequency. Additionally, a notch filter can be used to generate a notched signal by attenuating frequency components of the second chopping circuit's output signal that are at the chopping frequency. Thereafter, the notched signal can be amplified to generate the amplifier's output signal.
The second chopping circuit can operate to upshift the input offset voltage of the amplifier's input stage from DC to the chopping frequency where it can be attenuated by the notch filter. Since the frequency spectrum of the input signal can be upshifted by the first chopping circuit and downshifted by the second chopping circuit, the input signal can pass through the notch filter without attenuation.
Although configuring the amplifier to include the chopper circuitry and the notch filter can reduce the amplifier's input offset voltage, mismatch error in the notch filter can result in the amplifier nevertheless having offset and/or the amplifier's output signal having ripples at the chopping frequency and at harmonics thereof.
There is a need for notch filters having improved performance. Additionally, there is need for chopper-stabilized amplifiers having reduced input offset voltage and/or reduced output voltage ripple.