Dual Tone Multi-Frequency (DTMF) signalling (also known as Touch-Tone, Tel-Touch,etc.) has gained importance in the world of telecommunications (telephony, answering machines, remote control, credit cards, etc) at the expense of dial-pulse signalling due to its more efficient and higher reliability for transmission of signals.
This paper presents a high performance DTMF receiver able to operate in the range of 3V-5V of voltage supply with a low current consumption (<1mA) that is virtually fixed. In addition, on-chip test facilities for the analog part have been incorporated into the chip, in particular: a) a modified opamp (called sw-opamp) has been used to provide external accessing to inputs and outputs of the main analog blocks for off-line test purposes and, b) a Built-In-Self-Test strategy based on converting the analog part into an oscillator (the so-called oscillation-based-test) to perform a structural testing of the architecture. An integrated prototype has been designed and integrated in a 0.6μm technology. The price paid for such on-chip test facilities is very low; concretely, just an extra pin is used, power consumption during normal operation is not penalized and the area overhead is in the order of 7%. The experimental results demonstrate the good performance of the design and the feasibility of the testing approaches.