DS8907 Datasheet | National Semiconductor

Description The DS8907 is a PLL synthesizer designed specifically for use in AM FM radios It contains the reference oscillator a phase parator a charge pump a 120 MHz ECL I2L dual modulus programmable divider and an 18-bit shift register latch for serial data entry The device is designed to operate with a serial data controller generating the necessary division codes for each frequency and logic state information for radio function inputs outputs The Colpitts reference oscillator for the PLL operates at 4 MHz A chain of dividers is used to generate a 500 k Hz clock signal for the external controller Additional dividers generate a 25 k Hz reference signal for FM and a 10 k Hz reference signal for AM One of these reference signals is selected by the data from the controller for use by the phase parator Data is transferred between the frequency synthesizer and the controller via a 3 wire bus system This consists of a data input line an enable line and a clock line When the enable line is low data can be shifted from the controller into the frequency synthesizer When the enable line is transitioned from low to high data entry is disabled and data present in the shift register is latched From the controller 20-bit data stream the first 2 bits address the device permitting other devices to share the same bus Of the remaining 18-bit data word the next 13 bits are used for the PLL divide code The remaining 5 bits are connected via latches to output pins These 5 bits can be used to drive radio functions such as gain mute FM AM and stereo only These outputs are open collector Bit 16 is used internally to select the AM or FM local oscillator input and to select between the 10 k Hz and 25 k Hz reference A high level at bit 16 indicates FM and a low level indicates AM The PLL consists of a 13-bit programmable I2L divider an ECL phase parator an ECL dual modulus (p p a 1) prescaler and a high speed charge pump The programmable divider divides by (N a 1) N being the number loaded into...