Sinusoidal incremental encoders are different from the normal ones being the available outgoing signals not square waves ones (digital), but of sinusoidal type (analogue).
These transducers are particularly suitable for motors with feedback sensor function. They ensure an improvement of dynamic performances compared to normal systems. In order to ensure high engine steering performances from the converter, the encoder feedback has to supply a great number of pulses, mostly in case of low engine feedback speed.
The use of traditional incremental encoders with high pulses is a problem because of the difficulty in transmitting and treating the digital signal when the motor whirls at high speed, for example 6000 rpm, in this case the band width required by the engine to treat the encoder signals at 18000 rpm, would largely exceed the MHz threshold.
The use of sinusoidal analogue signals allows a considerable limitation of the above mentioned problem by successfully simulating a high pulses encoder. This is possible by interpolating the analogue signals of two sinusoids desynchronised each other of 90 electrical degrees (sine and cosine) to calculate the rotation angle.
You can easily achieve high multiplications of the basic sinusoids obtaining for example more than 100000 pulses/round from a 1024 sinusoid /round encoder. A little more than 100 kHz is the sufficient band width necessary to the signal reception, for example 6000 rounds.
The signals outgoing from the encoder, consist of two sinusoids desynchronised of 90 electrical degrees, usually called sine and cosine, and of a zero signal balanced between the two sinusoidal signals.
The shape of  the zero signal, being analogue too, is similar to a sinusoid semi period and it can be easily squared in order to produce a referring pulse with a opening angle being variable according to the “trigger” level previously set.
In sinusoidal encoders, it is possible to integrate two sinusoidal signals with a period equal to 360 mechanical degrees = 1 sinusoid per round having the function of commutating signals in case of employment on brushless engines. 
The outputs with 1 sinusoid/round are useful as it is possible to obtain from them the absolute angular position of the encoder using it as a resolver.
All outputs of ELCIS sinusoidal encoders are provided with complementary sinusoids so that the User can easily treat signals and for a better protection against disturbs in the signal transmission.
The precision of these sinusoidal encoders is given by the quality of the sinusoids which must have the lowest quantity of harmonics (low distortion) and a good linearity on the entire rotation.
A further important factor is the extension stability and the absence of offsets of the sinusoids at any change of the speed (rpm) and at any change of temperature and input tension.
ELCIS sinusoidal encoders, thanks to sophisticated technologies, grant a distortion of sinusoids ≤1,5% and a width variation within 3 dB until an outgoing frequency equal to 160 kHz with void cc offset in the entire temperature interval from 0÷70° C.
We remind that:

Encoder frequency [Hz] = (rpm shaft engine/60)   * nr. sinusoids round