原创 ACAM TDC:TDC-GPX精度可调举例

Q:  I’m planning to use the device in a specified temperature range, e. g. between –20 °C to +50 °C. So what resolution should be selected, in order to be sure that the device stays locked within the whole temperature range?

A: In this case there are two items that mainly have to be considered. First the intrinsic resolution of the device that slightly varies from chip to chip, and secondly the temperature range that is specified in your application.

At 3.3V Vddc and 25 °C junction temperature the intrinsic resolution of the TDC-GPX ranges typically between 68ps to 89 ps.Additionally, the above specified environmental temperature range of your application introduces an additional timing variation. Basically the resolution degrades at rising and improves at lower temperatures, but the dependencies are described in detail in the “General Timings & Resolution”-Section of the TDC-GPX datasheet. The following two extremes have to be considered:

• At -20°C the resolution of the devices, that are specified with 68ps resolution increases to 0.923 x 68ps = 60 ps.
• At +50 °C the timing of the devices with 89ps decreases to 1.043 x 89 = 92.8 ps.

Or in order words, without resolution adjust the GPX resolution may vary between 60ps to about 93ps for the above specified temperature range. This has to be compensated by regulating the supply voltage of the measurement core’s hardmacro (Vddcc-h).

The maximal adjustment range lies between 2.3 V and 3.6 V, so we again have to consider the following limitations:

• With Vddc-h = 2.3V the 60ps resolution can be degraded to 60ps x 1.4 = 87.8ps
• With Vddc-h = 3.6V the 92.8ps resolution can be improved to 92.8ps x 0.93 = 86.3 ps.

In other words again: The timing of the devices with 60ps resolution can be degraded to 87.8ps by decreasing Vddc-h to 2.3 V. The timing of the devices with 92.8ps resolution can be improved to 86.3ps by increasing Vddc-h to 3.6 V. Selecting a resolution between 87.8 and 86.3ps now ensures that the TDC-GPX stays locked within -20°C to +50 °C.