Apparatus and method for locking onto a psuedo-noise code in an IS-95 spread spectrum communications system

An apparatus for locking onto a received pseudo-noise code, the apparatus comprising:

• a pseudo-noise generator, coupled to receive a timing adjust signal and in response generate an early pseudo-noise signal delayed by less than one-half of a chip interval relative to an on-time pseudo-noise signal, and
• a late pseudo-noise signal advanced by less than one-half of a chip interval relative to the on-time pseudo-noise signal;
• an adder for subtracting the late from the early pseudo noise signal to generate a difference signal,
• a correlator, coupled to the adder for receiving the difference signal and a received spread spectrum signal, and for multiplying the received spread spectrum signal with the difference signal to generate a resulting product signal,
• an integrator to integrate the resulting product signal,
• a decimator for decimating the integrated resulting product signal,
• a loop filter to shape the decimated, integrated product signal, and
• an interpolator for interpolating the shaped, decimated and integrated product signal, and
• a numerical controlled oscillator for receiving the interpolated, shaped, decimated and integrated product signal and generating said timing adjust signal,
• wherein a loop is created in which the received spread spectrum signal tracks the pseudo-noise code.