Provided are a CIS circuit that does not increase an initial voltage charge time allocated by a CDS even if a pixel size is reduced and a method of providing an initial charge to the CIS circuit. The CIS circuit may include an APS block, a current source block and a charge supply block. The APS block may output APS signals from APS output terminals in response to sensed image transfer signals, pixel select signals and pixel reset signals. The current source block may control currents flowing from the APS output terminals to a power supply in response to a bias voltage. The charge supply block may provide a quantity of charges to the APS output terminals in response to a representative reset signal and a pre-resent signal.