An impedance calibration circuit for bidirectional transmission of high-speed interface circuits

In the high-speed serial interface with bidirectional transmission function, the two resistors at the transmitter's output have a great impact on the performance of the circuit. In order to improve the performance of the circuit in complex environment, impedance calibration is required. The traditional impedance calibration has the drawbacks of high power consumption, large area, large system error and long convergence time. To solve the above problems, this paper designs an impedance calibration circuit for two-way transmission of high-speed serial interface. By sharing current sources, the area and power consumption of the impedance calibration circuit are effectively reduced, and the system error caused by current source mismatch is eliminated. A comparator with misalignment elimination is introduced, and the system error of the calibration circuit is reduced by optimizing the leakage of the switch tube and the clock feed-through in the comparator. Successive Approximation Register (SAR) logic is also used to find the best resistance calibration control code, which reduces the convergence time. A high precision, low power consumption impedance calibration circuit is implemented in SMIC 40 nm process, which can adjust two resistors separately. The two resistors to be calibrated are analyzed by Monte Carlo, and the impedance calibration 3σ values are 201.76 mΩ and 198.80 mΩ, respectively. The overall power consumption of the impedance calibration circuit is 4.205 mW.