AEAS-7000 Ultra-precision 16 bit Gray Code Absolute Encoder Module Data Sheet Description Features The encoder IC consists of 13 signal photo diode channels Minimum mechanical alignment during installation and 1 monitor photo diode channel and is used for the Two Sine/Cosine true diff erential outputs with 1024 optical reading of rotary carriers (i.e., discs). The photo- periods for unit alignment diodes are accompanied with precision amplifi ers plus Integrated highly collimated illumination system additional circuitry. 11 digital tracks plus 2 sin/cos tracks generate precise The monitor channel is used to drive a constant current 16 bit Gray code source for the highly collimated IR illumination system. Ultra fast, 1 s cycle for serial data output word equals 16 MHz Functional Description On-chip interpolation and code correction Background MSB can be inverted for changing the counting The 13 signal channels are set up as: direction 1. Two precision defi ning signals (A0, A09), which are Internally built-in monitor track for tracking the light two 90 electrical shifted sine, cosine signals. These level of the LED. signals are conditioned to be compensated for off set Watch dog with alarm output and gain errors. After conditioning they are on chip 25C to +85C operating temperature interpolated 2. 11 analog (A1-A11) channels which are directly digitized Applications by precision comparators with hysterisis tracking. The Rotary application up to 16 bit/360 absolute position digitized signals are called D1-D11. Linear positioning system An internal correction and synchronization module allows the composition of a true 16 bit Gray code by merging Cost eff ective solution for direct integration into OEM the data bits of (1) and (2) by still keeping the code systems monotonic. There is a Gray code correction feature for this encoder. This Gray code correction can be disabled/enabled by the pin KORR. The gain and off set conditioning value of the sine and cosine signals are preloaded on-chip by factory. This will compensate for mechanical sensor misalignment error.Signal-Channels A1-A11 LSB Gray Code Correction (Pin KORR) The photocurrent of the photo diodes is fed into a trans- This function block synchronizes the switching points for impedance amplifi er. The analog output of the amplifi er the 11 bit Gray code of the digital signals D1 to D11 with has a voltage swing of (dark/light) about 1.3 V. Every output D0 and D09 (digitized signal of A0 and A09). is transformed by precision comparators into digital signals This Gray code correction only works for the 12 bit MSB (D1-D11). The threshold is at VDD/2 (=Analog-reference), (4096 steps per revolution). regulated by the monitor channel. The correction is not for the 4 excess interpolated bits of Monitor Channel with LED Control at Pins LEDR and LERR the 16 bit Gray code. The analog output signal of the monitor channel is Gray code correction can be switched on or off by putting regulated by the LED current. An internal bipolar transis- the pin KORR =1(on) or =0(off ). tor sets this level to VDD/2 (control voltage at pin LEDR). Thus the signal swing of each output is symmetrical to MSBINV and DOUT Pins VDD/2 (=Analog-reference) The serial interface consists of a shift register. The most The error bit at pin LERR is triggered if the Ve of the internal signifi cant bit, MSB (D11) will always be sent fi rst to DOUT. bipolar transistor is larger than VDD/2. The MSB can be inverted (change code direction) by using pin MSBINV. Signals Channels A0, A09 with Signal Conditioning and DIN and NSL Pins Calibration The serial input DIN allows the confi guration as ring These two channels give out a sine and cosine wave, register for multiple transmissions or for cascading 2 or which are 90 degree phase shifted. These signals have more encoders. DIN is the input of the shift register that amplitudes which are almost constant due to the LED shifts the data to DOUT. current monitoring. Due to amplifi er mismatch and mechanical misalignment, the signals have gain and The NSL pin controls the shift register, to switch it between off set errors. These errors are eliminated by an adaptive load (1) or shift (0) mode. Under load mode, DOUT will signal conditioning circuitry. The conditioning values are give the logic of the MSB, i.e., D11. on-chip preprogrammed by factory. The analog output Under shift mode (0), coupled with the SCL, the register signals of A0 and A09 are supplied as true-diff erential will be clocked, and gives out the serial word output bit by voltage with a peak to peak value of 2.0 V at the pins A09P, bit. As the clock frequency can be up to 16 MHz, the trans- A09N, A0P, A0N. mission of the full 16 bit word can be done within 1 s. Interpolator for Channels A0, A09 Valid data of DOUT should be read when the SCL clock is low. Please refer to timing diagram (Figure 3). The interpolator generates the digital signals D0, D09 and D-1 to D-4. The interpolated signals D-1 to D-4 extend the 12 bit Gray code of the signals D11.D0 to form a 16 bit Gray code. D0 and D09 are digitized from A0 and A09. The channels A0-A11 and A09 have very high dynamic bandwidth, which allows a real time monotone 12 bit Gray code at 12000 RPM. The interpolated 16 bit Gray code can be used up to 1000 RPM only. At more than 1000 RPM, only the 12 bit Gray code from the MSB side can be used. 2