Semiconductor device

1 . A semiconductor device comprising:

a transmission circuit configured to output an analog signal; and

a receiving circuit configured to receive an input signal which is transmitted from a target object in response to the analog signal,

wherein the semiconductor device operates by alternately repeating a transmission period that to transmit the analog signal and a reception period that to receive the input signal,

wherein the receiving circuit comprises a gain control circuit configured to sample the input signal during the reception period, and to control a gain of the receiving circuit based on the sampled input signal during the transmission period,

wherein the gain control circuit comprises:

a gain adjustment circuit configured to amplify the input signal according to the gain, and

an analog-to-digital converting circuit configured to analog-to-digital convert the amplified input signal,

wherein the gain adjustment circuit comprises:

a threshold detection circuit configured to detect an amplitude information related to an amplitude of the input signal;

a setting control circuit configured to set the gain during the transmission period; and

an output circuit configured to output the gain set by the setting control circuit, and

wherein the threshold circuit comprises:

a holding circuit configured to hold the amplitude information during the reception period; and

a reset circuit configured to reset the amplitude information when the reception period finishes.

2 . The semiconductor device according to claim 1 , wherein the threshold detection circuit and the gain adjustment circuit are disposed near the receiving circuit than the analog-to-digital conversion circuit in the gain control circuit.

3 . The semiconductor device according to claim 1 ,

wherein the analog-to-digital conversion circuit comprises a sample-and-hold circuit and a voltage comparation circuit, and is activated while the amplitude information is held during the reception period.

4 . The semiconductor device according to claim 1 , wherein the analog-to-digital conversion circuit comprises a plurality of sample-and-hold circuits and a plurality of voltage comparation circuits,

wherein the plurality of the sample-and-hold circuit sample the amplified input signal at different timings, and

wherein the analog-to-digital conversion circuit is activated while the gain is not adjusted during the transmission period.

5 . The semiconductor device according to claim 1 ,

wherein the analog-to-digital conversion circuit comprises a plurality of sample-and-hold circuits and a plurality of voltage comparation circuits, and

wherein the plurality of the voltage comparation circuits inputs a reference voltage, and are configured to control an amplitude or its absolute value of the reference voltage based on the amplitude information.