A microcircuit tone generator for push-button dialing

A new microcircuit tone generator fabricated with tantalum thin film and a custom IC in a dual-in-line plastic pack is described. Novel designs of filter, amplifier, and amplitude limiting have been used that enable operation over a wide frequency range, wide supply voltage range, and wide temperature range while maintaining excellent stability. Interfacing of the tone generator is very flexible enabling it to be used in most telephone and data systems. Frequency selection switches with up to 150-/spl Omega/ resistance are permissible, without pulling effects, so that low-cost conductive rubber push-button pads and electronic switching can be used directly. The feedback filter configuration used in the oscillator design is gain insensitive so that only frequency has to be trimmed, making rapid automatic trimming possible in manufacture. The primary applications for this device is for telephone systems, but it is also useful in the general purpose low-frequency oscillator area.