Frequency synthesis loop having controlled loop gain

#1. Fields of the Invention

#The invention relates generally to frequency shift key (FSK) signal generators and more particularly to an FSK generator having high speed automatic calibration loops for determining phase gain and phase preemphasis correction coefficients and then using feedforward compensation for providing precisely shaped frequency transitions between modulation states in a burst mode modulated signal. The invention also relates particularly to a frequency hopping signal generator using phase gain coefficients for stabilizing loop gain of a frequency synthesis loop. The invention also relates particularly to an apparatus and a method for dynamic measurement of phase error of a modulated signal.

#2. Description of the Prior Art

#FIG. 1 is a block diagram of a Gaussian minimum frequency shift key (GMSK) transmitter of the present invention;

#FIG. 2 is a block diagram of a frequency synthesizer of the transmitter of FIG. 1;

#FIG. 3 is a block diagram of a feedforward converter of the transmitter of FIG. 1;

#FIG. 1 is a block diagram of a Gaussian minimum shift key (GMSK) signal generator or transmitter referred to by the general reference number 10 for providing a radio frequency (RF) GMSK frequency modulated output signal. The GMSK transmitter 10 is described herein as adapted for the Global System for Mobile Communications (GSM). However, the idea of the GMSK transmitter 10 of the present invention can be applied to other systems where the accuracies of the modulation states and the paths of the transitions between the modulation states is important. GSM is also known as Groupe Speciale Mobile.

#The GMSK transmitter 10 includes a Gaussian input data shaper 12, an input mode switch 14, an output mode switch 16, a frequency synthesizer 20, a phase coefficient memory 22, a feedforward converter 30, a phase gain compensator 40, a phase preemphasis compensator 50, a phase quantizer 60, and a switched loop phase detector 70.

#The GMSK transmitter 10 has two modes: a calibration mode where compensation coefficients are determined and an on-line operation mode where the compensation coefficients are used to improve the precision of the modulation for transmitting communication data. An initial or full calibration is used when the GMSK transmitter 10 is turned on or by request from system software, and a burst calibration is used during designated burst time slots interspersed with the burst time slots of on-line operation. For a calibration (initial or burst) the mode switch 14 first selects a fixed level, preferably 0, and then a pseudorandom binary sequence (PRBS). For on-line operation, the mode switch 14 selects on-line binary data to be transmitted. The mode switch 14 passes the selection to the Gaussian shaper 12.