Syncronizing a data acquisition device with a host
First Claim
1. In a data acquisition pod of the type having a signal sampling A/D converter that is coupled to a host system via a data communication link, apparatus for synchronizing a host-derived reference clock signal with a clock signal in the data acquisition pod that operates the A/D converter, so that the A/D converter provides samples to the data communication link at the same rate as the rate at which the host system requests the samples, comprising:
- a decoder having an input coupled to the data communication link for extracting from communication received from the host a host reference signal having a host reference frequency;
a clock signal source for developing an A/D reference clock signal having a frequency that is offset a predetermined amount from the frequency of the host reference frequency;
an A/D converter of the oversampling type having an A/D converter clock signal input; and
a pulse modifying digital phase-locked loop (PLL) responsive to the A/D reference clock signal and the host reference signal for developing an A/D clock signal in which one of its clock periods is periodically modified, said A/D reference clock signal being coupled to said A/D converter clock signal input, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples.
5 Assignments
0 Petitions
Accused Products
Abstract
Apparatus for synchronizing a reference clock signal received from a host system with an A/D converter clock signal generated in a data acquisition pod. The pod includes a decoder responsive to communication received from the host for extracting a host reference signal, and a clock signal source for developing an A/D reference clock signal having a frequency that is different from the frequency of the host reference signal. A pulse modifying digital phase-locked loop (PLL) is responsive to the A/D reference clock signal and the host reference signal for developing an A/D clock signal for an A/D converter in which one of its clock periods is periodically modified, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples. In a preferred embodiment the pod also includes a signal detector for detecting a specified alignment in time of the readiness of the A/D converter to provide a given sample with a host system request for that given sample, and upon such detection, selectively providing an enable signal to the PLL, thereby enabling operation of the PLL and synchronizing the host and pod clock rates, as well as locking in a given alignment the providing to the host of the samples developed by the A/D converter with the host system requests for those samples.
-
Citations
19 Claims
-
1. In a data acquisition pod of the type having a signal sampling A/D converter that is coupled to a host system via a data communication link, apparatus for synchronizing a host-derived reference clock signal with a clock signal in the data acquisition pod that operates the A/D converter, so that the A/D converter provides samples to the data communication link at the same rate as the rate at which the host system requests the samples, comprising:
-
a decoder having an input coupled to the data communication link for extracting from communication received from the host a host reference signal having a host reference frequency; a clock signal source for developing an A/D reference clock signal having a frequency that is offset a predetermined amount from the frequency of the host reference frequency; an A/D converter of the oversampling type having an A/D converter clock signal input; and a pulse modifying digital phase-locked loop (PLL) responsive to the A/D reference clock signal and the host reference signal for developing an A/D clock signal in which one of its clock periods is periodically modified, said A/D reference clock signal being coupled to said A/D converter clock signal input, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
-
-
12. A method for synchronizing a reference clock signal that operates a host system with a clock signal developed in a data acquisition pod that operates an A/D converter in the pod, so that the A/D converter provides samples to a data communication link connecting the host and pod at the same rate as the rate at which the host system requests the samples, the method comprising:
-
decoding communications received over the data communication link from the host system for extracting a host reference signal having a host reference frequency; providing a clock signal source for an A/D reference clock signal having a frequency that is different from the host reference frequency; developing a sequence of a plurality of digital samples of at least one analog input signal using an oversampling type of A/D converter having an A/D converter clock signal input; and developing an A/D clock signal that is synchronized with the host reference signal by using a pulse modifying phase-locked loop (PLL) responsive to the A/D reference clock signal and the host reference signal, said PLL causing one of the clock periods of the A/D clock signal to be periodically modified, said A/D reference clock signal being coupled to said A/D converter clock signal input, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
-
Specification