Analog frontend circuit and signal filtering method for photoplethysmography

An analog frontend circuit for photoplethysmography, comprising:

• a first current control circuit, coupled with a first node, and configured to generate a first sub-current, wherein the first sub-current is part of an input current flowing to the first node;
• a monitoring circuit, coupled with the first node, and configured to receive a reference voltage, wherein in a tracking period, the monitoring circuit is configured to control the first current control circuit to determine a magnitude of the first sub-current, in order to control a voltage of the first node to track the reference voltage;
• and
• a reading circuit, coupled with the first node through the monitoring circuit,
• wherein in a sensing period after the tracking period, the monitoring circuit is configured to control the first current control circuit to keep the first sub-current to have the magnitude of the first sub-current determined in the tracking period,
• wherein after the first sub-current is kept, the monitoring circuit is configured to transmit a second sub-current from the first node to the reading circuit so that the reading circuit is configured to convert the second sub-current to an output voltage, wherein the second sub-current is part of the input current.