School of Electronics and Information, Information and Communication System-on-chip (SoC) Research Center, Kyung Hee University, Yongin 17104, Korea.
Sensors (Basel). 2018 Nov 15;18(11):3948. doi: 10.3390/s18113948.
Herein, we present a low-power cyclic Vernier two-step time-to-digital converter (TDC) that achieves a wide input range with good linearity. Since traditional approaches require a large area or high power to achieve an input range >300 ns, we solve this problem by proposing a simple yet efficient TDC suitable for time-of-flight (TOF) sensors. In previous studies using the cyclic structure, the effect of startup time on the linearity of the TDC is not described. Thus, the achievable linearity has been limited when the TDC is used for applications requiring a high input range. We solve this problem by using a simple yet effective technique to compensate. The proposed technique is realized using (1) digitally-controlled oscillators (DCOs) that have dual frequency control and matched startup time; (2) an alignment detector that performs startup time correction by proper timing control; and (3) a fully symmetric arbiter that precisely detects the instant of edge alignment. To achieve a fine resolution for the cyclic Vernier TDC, we design two closely-matched DCOs with dual frequency control. The alignment detector performs the critical task of cancelling startup time via timing control. The detector is delay-compensated by using a dummy to provide matched loading for the two DCOs. To enhance the detection speed under low power, a current-reuse approach is employed for the arbiter. The TDC is fabricated using a 0.18 μm complementary metal⁻oxide⁻semiconductor (CMOS) process in a compact chip area of 0.028 mm². Measured results show a dynamic range of 355 ns and a resolution of 377 ps. When the result is applied for TOF sensing, it corresponds to a distance range of 53.2 m and a resolution of 5.65 cm. Over a relatively large input range, good linearity is achieved, which is indicated by a DNL of 0.28 LSB and an INL of 0.96 LSB. The result corresponds to root mean square (RMS) error distance of 5.42 cm. The result is achieved by consuming a relatively low power of 0.65 mW.
本文提出了一种低功耗循环游标两步时间数字转换器（TDC），该转换器具有较宽的输入范围和良好的线性度。由于传统方法需要较大的面积或较高的功率才能实现 >300ns 的输入范围，因此我们通过提出一种适用于飞行时间（TOF）传感器的简单而高效的 TDC 来解决此问题。在以前使用循环结构的研究中，并未描述启动时间对 TDC 线性度的影响。因此，当 TDC 用于需要高输入范围的应用时，其可实现的线性度受到限制。我们通过使用一种简单而有效的技术来解决此问题进行补偿。该技术通过以下方式实现：（1）使用具有双频控制和匹配启动时间的数字控制振荡器（DCO）；（2）通过适当的定时控制执行启动时间校正的对准检测器；（3）精确检测边沿对准瞬间的全对称仲裁器。为了实现循环游标 TDC 的精细分辨率，我们设计了两个具有双频控制的紧密匹配的 DCO。对准检测器通过定时控制执行关键的启动时间消除任务。通过使用虚拟元件为两个 DCO 提供匹配的负载，来对检测器进行延迟补偿。为了在低功率下提高检测速度，采用了电流复用方法来实现仲裁器。该 TDC 使用 0.18μm 互补金属氧化物半导体（CMOS）工艺在 0.028mm²的紧凑芯片面积上制造。测量结果显示，动态范围为 355ns，分辨率为 377ps。当将结果应用于 TOF 感测时，它对应于 53.2m 的距离范围和 5.65cm 的分辨率。在相对较大的输入范围内，实现了良好的线性度，其表现为 0.28LSB 的 DNL 和 0.96LSB 的 INL。结果对应于均方根（RMS）误差距离为 5.42cm。通过消耗相对较低的 0.65mW 功率来实现此结果。
