Codec Testing Using Synchronized Analog And Digital Signals

Five methods for verifying coder/decoder operation in telecommunications PC boards provide the engineer optimal fault coverage with minimal test time. All methods support a dual-purpose testing strategy: (1) to conduct an in-circuit board test to detect assembly errors before a functional test and (2) to conduct a functional test in which stress is applied to detect marginal performance. All methods involve the use of synchronized analog and digital signals with optional IEEE-488 instruments for detail inspection. The first two methods, coder testing and decoder testing, are appropriate techniques for traditional in-circuit testing. The next two methods, analog loopback testing and digital loopback testing, are considered quasi-functional tests. The test signal path between stimulus and response may traverse a number of different ICs but not dynamically test complete board operation. The last method, functional instruments testing, allows detailed performance parameters specific to the device being tested to be verified. Sample test programs are presented for each method.