Front-end circuit and encoder

An encoder comprising:

• a scale in which a scale track is disposed;
• a detection head configured to output signals of two or more phases indicating a detection result of the scale;
• and
• a signal processing apparatus comprising a front-end circuit configured to receive signals corresponding to two phases in the signals of two or more phases, wherein
• the front-end circuit comprises:
• a preamplifier configured to amplify signals input to first and second input terminals;
• a first switching circuit configured to receive first and second input signals and to alternatively and respectively output the first and second input signals to the first and second input terminals;
• a switched capacitor circuit configured to sample two signals amplified by the preamplifier;
• an integration circuit configured in such a manner that differential signals that are two signals sampled by the switched capacitor circuit are respectively input to third and fourth input terminals and configured to output differential signals obtained by integrating the signals input to the third and fourth input terminals to first and second output terminals;
• and
• a second switching circuit configured to switch a connection relationship between the switched capacitor circuit and the integration circuit, wherein
• double correlation sampling in which a cycle including sampling by the switched capacitor circuit and signal integration by the integration circuit is performed twice is performed, and
• each time the cycle changes, the first and second switching circuits switch a connection relationship between the preamplifier and the first and second input terminals, and a connection relationship between the switched capacitor circuit and the integration circuit.