The present invention relates in one aspect to a microphone circuit assembly for an external application processor such as a programmable Digital Signal Processor. The microphone circuit assembly comprises a microphone preamplifier and analog-to-digital converter generate microphone signal samples at a first predetermined rate. A speech feature extractor is configured for receipt and processing of predetermined blocks of the microphone signal samples to extract speech feature vectors representing speech features of the microphone signal samples. The microphone circuit assembly additionally comprises a speech vocabulary comprising a target word or target phrase of human speech encoded as a set of target feature vectors and a decision circuit is configured to compare the speech feature vectors generated by the speech feature extractor with target feature vectors to detect the target speech word or phrase. A controller is configured to generate a recognition signal on an externally accessible output terminal of the microphone circuit assembly in response to a recognized target word or phrase in the microphone signal samples. Additional aspects of the invention relates to Digital Signal Processing Systems comprising the microphone circuit assembly.