Calibrating jitter
View Patent ↗Calibrating jitter in a communication channel between test equipment and a connection for a device under test (DUT) includes sampling test data in the communication channel at about a point of the connection to produce sampled data, where the test data travels through the communication channel at a first rate, and where the test data is sampled at a second rate that is less than the first rate, determining a first amount of jitter in the sampled data relative to the test data, and determining a second amount of jitter at about the point of connection based on the first amount of jitter.
1. A method of determining jitter from a communication channel between test equipment and a connection for a device under test (DUT), the method comprising:
connecting a sampling device to the communication channel in lieu of connecting the DUT to the communication channel, the sampling device being connected to the communication channel at a point where the DUT would connect to the communication channel;
using the sampling device to sample test data in the communication channel at the point where the DUT would connect to the communication channel, wherein the test data travels through the communication channel at a fist rate, wherein the test data is sampled at a second rate that is less than the first rate, and wherein test data is output by test equipment to the point where the DUT would connect to the communication channel, jitter being introduced into the test data by passage of the test data through the communication channel and appearing at the point where the DUT would connect to the communication channel;
determining a first amount of jitter in the sampled data relative to the test data; and
determining a second amount of jitter at the point where the DUT would connect to the communication channel, the second amount of jitter comprising the jitter introduced by the passage of the test data through the communication channel.
2. The method of claim 1 , wherein determining the second amount of jitter comprises substantially removing effects of jitter from one or more other sources.
3. The method of claim 2 , wherein the jitter from one or more other sources comprises jitter introduced by the sampling device and jitter introduced by a strobe used to clock the sampling device.
4. The method of claim 2 , wherein the jitter from one or more other sources comprises jitter introduced by the sampling device.
5. The method of claim 1 , wherein the sampling device comprises a latched comparator.
6. The method of claim 1 , wherein the sampling device comprises a D flip-flop.
7. The method of claim 1 , further comprising:
the test equipment adding jitter to the test data, the jitter added by the test equipment comprising at least one of periodic jitter and deterministic jitter.
8. A system for determining jitter from a communication channel, comprising:
a sampling device connected to the communication channel in lieu of connecting a device under test (DUT) to the communication channel, the sampling device being connected to the communication channel at a point where the DUT would connect to the communication channel, the sampling device being configured to sample test data in the communication channel to produce sampled data, the sampling device being configured to sample the test data at the point where the DUT would connect to the communication channel, wherein the test data travels through the communication channel at a first rate, wherein the test data is sampled at a second rate that is less than the first rate, and wherein test data is output by test equipment to the point where the DUT would connect to the communication channel, jitter being introduced into the test data by passage of the test data through the communication channel and appearing at the point where the DUT would connect to the communication channel; and
a processing device to:
determine a first amount of jitter in the sampled data relative to the test data; and
determine a second amount of jitter at the point where the DUT would connect to the communication channel, the second amount of jitter comprising jitter introduced by passage of the test data through the communication channel.
9. The system of claim 8 , wherein determining the second amount of jitter comprises substantially removing effects of jitter from one or more other sources.
10. The system of claim 9 , wherein the jitter from one or more other sources comprises jitter introduced by the sampling device and jitter introduced by a strobe used to clock the device.
11. The system of claim 9 , wherein the jitter from one or more other sources comprises jitter introduced by the sampling device.
12. The system of claim 8 , wherein the sampling device comprises a latched comparator.
13. The system of claim 8 , wherein the sampling device comprises a D flip-flop.
14. The system of claim 8 , further comprising:
the test equipment to add jitter to the test data, the jitter added by the test equipment comprising at least one of periodic jitter and deterministic jitter.
15. The system of claim 8 , wherein the sampling device is configured to sample the test data in accordance with a clock signal; and
wherein the system further comprises:
a clock distribution device to receive the clock signal and to provide the clock signal to the sampling device.
16. The method of claim 1 , wherein determining the second amount of jitter comprises comparing the first amount of jitter to a total amount of jitter in a signal that has been reconstructed from the sampled data.
17. The system of claim 8 , wherein determining the second amount of jitter comprises comparing the first amount of jitter to a total amount of jitter in a signal that has been reconstructed from the sampled data.