PMB2308

The PMB 2308, PMB 2309 are Phase Locked Loop (PLL) synthesizers with programmable frequency dividers for use in mobile communication equipment. It is fabricated using Siemens B6HF silicon bipolar process.

The circuit of PMB2308 consists of high speed dual modulus divider, shift register, programmable counter (A-, N- and R-counter),phase detector with charge pump and a control logic block.

Since the high speed dual modulus divider is able to handle frequencies of up to 1.25 (2.5) GHz, there is no need to add a dedicated external prescaler. The switching signals for the dividing ratio 16/17 (32/33) is generated by the A-counter.

The A-counter and the N-down-counter of PMB2308 are programmable via the 3-wire bus. They are clocked by the dual modulus divider output signal. The carry output of the N-counter is connected to the frequency input of the phase detector and is controlling the loading of the programmed A-/N-counter start values.

The 11 bit R-counter of PMB2308 is also programmable and is serving as reference frequency divider. Its carry output is connected to the reference frequency input of the phase detector and is controlling the loading of the programmed counter start value.

The phase detector of PMB2308 is of PFD-type (phase and frequency sensitive). It has a linear output characteristic in the 0°phase error region.

The control logic handles phase detector output polarity,charge pump output current of PMB2308 and software-generated powerdown (all circuit parts except the shift registers and data latches).