Head unit and liquid ejection apparatus

A liquid ejection apparatus comprising:

• a transport mechanism;
• and
• a head unit, wherein
• the head unit includes
• a piezoelectric element displaced according to a driving signal to cause a liquid to be ejected,
• a driving signal generation unit that generates the driving signal,
• a residual vibration signal generation circuit that outputs a change in an electromotive force of the piezoelectric element according to residual vibration, in a pressure chamber in communication with a nozzle, that occurs after supply of the driving signal, as a residual vibration signal,
• an analog differential residual vibration signal generation circuit that converts the residual vibration signal into an analog differential residual vibration signal,
• a demodulation circuit that demodulates the analog differential residual vibration signal and outputs a demodulated signal,
• an AD converter that converts the demodulated signal into a digital signal, and
• a determination unit that determines, based on the digital signal, a state in the pressure chamber.