LM1310N — National Semiconductor
PLL FM Stereo Demodulator
The LM1310N is a monolithic integrated circuit manufactured by National Semiconductor, designed to demodulate the composite MPX (Multiplex) signal in FM stereo receivers. It uses a PLL (Phase-Locked Loop) technique to separate the left (L) and right (R) channels from the composite signal, eliminating the need for external tuned coils and filters: tuning is performed with a single potentiometer that sets the internal VCO frequency.
The device also integrates automatic stereo/mono switching and drive for the stereo indicator lamp, reducing the number of external components required in the receiver design.
Key Features
- PLL stereo demodulation, no tuning coils required
- Automatic stereo/mono switching
- Built-in stereo indicator lamp driver
- Wide supply voltage range
- 14-pin DIP package
Electrical Specifications (typical)
| Parameter | Value |
|---|---|
| Supply voltage (Vcc) | 8 – 14 V |
| Supply current (Icc) | 13 mA |
| Max input voltage | 1 V rms |
| Typical output voltage | 485 mV rms |
| Total harmonic distortion (THD) | 0.3 % |
| Channel separation | 40 dB |
| Junction temperature (Tj) | -20 °C … +125 °C |
| Package | DIP-14 |
Pinout (DIP-14)
| Pin | Function |
|---|---|
| 1 | Vcc |
| 2 | Composite (MPX) signal input |
| 3 | Amplifier output |
| 4 | Left channel output (L) |
| 5 | Right channel output (R) |
| 6 | Stereo indicator lamp |
| 7 | Ground (GND) |
| 8, 9 | Switching filter |
| 10 | 19 kHz (pilot) output |
| 11 | Modulator input |
| 12, 13 | PLL loop filter |
| 14 | VCO oscillator RC network |
Equivalents / Second Sources
The LM1310N belongs to a widely second-sourced family of devices from the 1970s-80s, produced with the same architecture and pinout by multiple manufacturers:
- MC1310 / MC1310P — Motorola (pin-compatible)
- CA1310 — RCA Solid State ("RC Phase Lock Loop Stereo Decoder")
- µA1310 — Fairchild
- XR1310 — Exar
- BA1310 — Rohm
Its direct predecessor is the MC1309 (Motorola), while the more advanced successor is the MC1310N/MC1310E in a 16-pin DIP package with extended functionality.
Typical Applications
- FM stereo radio receivers
- Car radios
- Stereo cassette recorders
- Hi-Fi tuners
