Connecting circuit and communication interface

A connecting circuit connected to a preceding stage of a transmission circuit and configured to receive a baseband signal, the connecting circuit comprising:

• an isolation element connected between an input terminal and an output terminal;
• a signal midpoint detection circuit connected parallel to the isolation element;
• a bias adding circuit connected in series with the signal midpoint detection circuit;
• and
• an initial voltage value detection circuit connected to a frame detection circuit,
• wherein the initial voltage value detection circuit holds an initial voltage value of the baseband signal in accordance with a signal of the frame detection circuit, and outputs the initial voltage value to the signal midpoint detection circuit,
• the signal midpoint detection circuit detects a midpoint voltage from the baseband signal and the initial voltage value, and outputs the midpoint voltage to the bias adding circuit, and
• the bias adding circuit adds the midpoint voltage to a bias voltage for biasing the baseband signal.

A connecting circuit connected to a preceding stage of a plurality of transmission circuits and configured to receive a plurality of baseband signals, the connecting circuit comprising:

• a plurality of isolation elements respectively connected between a plurality of input terminals and a plurality of output terminals;
• a plurality of signal midpoint detection circuits connected parallel to the respective isolation elements;
• a plurality of bias adding circuits connected in series with the respective signal midpoint detection circuits;
• and
• an inter-channel interpolation VL detection circuit,
• wherein the inter-channel interpolation VL detection circuit detects a low-voltage signal among the plurality of baseband signals, and outputs the low-voltage signal to the respective signal midpoint detection circuits,
• the signal midpoint detection circuits detect a midpoint voltage from the baseband signals and the low-voltage signal, and output the midpoint voltage to the bias adding circuits, and
• the bias adding circuits add the midpoint voltage to a bias voltage for biasing the baseband signal.

A connecting circuit connected to a preceding stage of a plurality of transmission circuits and configured to receive a plurality of baseband signals, the connecting circuit comprising:

• a plurality of isolation elements respectively connected between a plurality of input terminals and a plurality of output terminals;
• a plurality of frame detection circuits connected parallel to the respective isolation elements;
• a plurality of switching elements connected in series with the respective frame detection circuits;
• a plurality of bias adding circuits connected in series with the respective switching elements;
• and
• a difference average midpoint voltage calculation circuit configured to receive an output of an inter-channel interpolation VL detection circuit and an output of an inter-channel interpolation VH detection circuit,
• wherein the inter-channel interpolation VL detection circuit detects a low-voltage signal among the plurality of baseband signals, and outputs the low-voltage signal to the difference average midpoint voltage calculation circuit,
• the inter-channel interpolation VH detection circuit detects a high-voltage signal among the plurality of baseband signals, and outputs the high-voltage signal to the difference average midpoint voltage calculation circuit,
• the difference average midpoint voltage calculation circuit outputs, to the switching elements, a midpoint voltage based on the output of the inter-channel interpolation VL detection circuit and the output of the inter-channel interpolation VH detection circuit,
• the switching elements output the midpoint voltage to the bias adding circuits in accordance with inputs from the frame detection circuits, and
• the bias adding circuits add the midpoint voltage to a bias voltage for biasing the baseband signal.