1. A microphone circuit assembly for connection to an external application processor, comprising: a microphone preamplifier comprising an input terminal for receipt of a microphone signal, an analog-to-digital converter configured for receipt of an output signal of the microphone preamplifier and generation of corresponding microphone signal samples at a first predetermined sample rate, a speech feature extractor 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, a speech vocabulary comprising a target word or target phrase of human speech encoded as a set of target feature vectors, a controller comprising a decision circuit configured to compare the speech feature vectors generated by the speech feature extractor with the target feature vectors to detect the target speech word or phrase, the controller being configured to generate a recognition signal on an externally accessible output terminal in response to a recognized target word or phrase in the microphone signal samples.