A 16-bit D/A converter formed on a single monolithic chip and having two cascaded stages each including a 256-R resistor string DAC. The analog output voltage of the first stage is coupled to the second stage by two buffer amplifiers each formed by a non-epitaxial process using a P-type substrate. The...http://www.google.de/patents/US4678936?utm_source=gb-gplus-sharePatent US4678936 - MOS-cascoded bipolar current sources in non-epitaxial structure
