National LM1800
The LM1800 is a second generation integrated FM Stereo Demodulator using phased lock loop techniques to regenerate the 38kHz subcarrier. The numerous features integrated in the chip's die enables the reproduction of high fidelity sound in inexpensive variety of home and automotive stereo receivers. In addition to separating the left and right signal information from the detected IF output, the LM1800 features automatic stereo/monaural switching, 45dB power rejection, and a 100mA stereo indicator lamp driver. Particularly attractive is the low external part count and total elimination of troublesome tuning coils. A single inexpensive potentiometer performs all tuning requirements.

There is a National application note describing the LM1800 in detail, AN-81, dated June 1973, co-authored by T.D. Isbell and David S. Mishler. Mr. Mishler, who still works at National, said that him and Mr. Isbell wrote the AppNote at approximately the same time the LM1800 came out into the market in 1973. The device was developed upon request from AC Delco as a product improvement from Motorola's LM1310 series. The added feature provides a smooth transition from stereo mode to mono blending of the audio signal. The last year in which the LM1800 was listed in National's data book was in 1990, possibly the last year it may have remained in the suppliers' inventory. The AppNote has since been made inactive from circulation, although we still have it in hardcopy at National's data library.

Further research revealed that the LM1800 has been replaced in today's market by UA758, which is a pin-for-pin copy of the LM1800. The lower limit for Theta JC is also improved to -40C. The UA758 is manufactured and distributed by Rochester Electronics, Inc. They may be accessed at