A circuit for converting a triangular waveform into a sinusoidal waveform using the non-linear transfer characteristic of a first transistor differential amplifier. Second and third differential amplifiers are parallel-connected to said first differential amplifier with the slopes of their transfer characteristics in opposite sense thereto and having their operating points shifted on their transfer characteristics in opposite directions with regard to each other and symmetrically to the operation point of said first differential amplifier so that the resulting overall transfer characteristic of said first, second and third differential amplifiers has zero slope at the extremal amplitudes of said triangular waveform.
Apparatus (20) for generating a sine shaped output signal at an output (Sn, Sp). The apparatus (20) comprises a first transistors (M1) and a second transistor (M2) being arranged as differential pair (22). The differential pair (22) has two input nodes (Tp, Tn) allowing a triangular input signal (V.sub.in(t)) with a given amplitude (A) to be applied between a gate (Tp) of the first transistor (M1) and a gate (Tn) of the second transistor (M2). The differential pair (22) further comprises a node (X) where a source of the first transistor (M1) and a source of the second transistor (M2) is connected. The sine wave shaped signal is provided between a drain (Sp) of the first transistor (M1) and a drain (Sn) of the second transistor (M2). A current mirror (21) is employed for feeding a predefined tail current (I.sub.ss) into/out of the node (X) of said differential pair (22). The differential pair (22) allows the first transistor (M1) and the second transistor (M2) to be operated in the saturation region such that the sine wave shaped output signal (I.sub.o; V.sub.out) is a nonlinear function of the triangular input signal (V.sub.in(t)).
The invention relates to the forming of a control pulse for the transmitter in a GSM radio telephone system. A cos.sup.2 pulse is formed by means of an analog circuit from a rectangular pulse which is first shaped into a triangular pulse which may be somewhat clipped at its peak. The triangular pulse is further shaped into a cos.sup.2 pulse. The circuit also includes the selection of the abruptness of the triangular pulse and, thereby, the abruptness of the cos.sup.2 pulse.
A burst mode digital communications system which is unique in that it modulates a sinusoidal carrier with discrete cosine segments. The discrete cosine segments may contain different time and amplitude values. The discrete cosine segments may be combined with each other or with zero slope level segments in order to effectively modulate the sinusoidal carrier. Rather than employing the use of filters for controlling instantaneous voltage changes, the present communications system forces the bit edges of the discrete cosine segments to occur at the zero slope points of a cosine wave, where no voltage changes occur. The communications system utilizes direct digital synthesis in order to create a carrier signal which closely represents sinusoidal carrier signal. The present communication system may be used in conjunction with various conventional methods such as phase-shift keying and amplitude-shift keying. A device is also disclosed for demodulating the carrier signal in order to recover the original base band signal. The burst mode digital communications system may also demodulate data by employing adaptive templates for more accurately determining received digital symbols.
