AEAS-7500

AEAS - 7500 Ultra-Precision 16 bit Gray Code Absolute Encoder Module Data Sheet Description The encoder IC consists of 13 signal photo diode channels and 1 monitor photo diode channel and is used for the optical reading of rotary or linear code carriers (i.e. discs or scales). The photodiodes are accompanied with precision amplifiers plus additional circuitry. The monitor channel is used to drive a constant current source for the highly collimated IR illumination system. Functional Description Background The 13 signal channels are set up as: 1. Two precision defining signals (A0, A09), which are two 90° electrical shifted sine, cosine signals. These signals are conditioned to be compensated for offset and gain errors. After conditioning they are on-chip interpolated and computed to a combined absolute 16 bit Gray code, together with signal channels A1-A11. 2. 11 analog (A1-A11) channels, which are directly digitized by precision comparators with hysteresis tracking. The digitized signals are called D1-D11. 3. An internal correction and synchronization module allows the composition of a true 16 bit gray code by merging the data bits of (1) and (2) by still keeping the code monotonic. 4. There is a Gray code correction feature for this encoder. This Gray code correction can be disabled/enabled by the pin KORR. 5. The gain and offset conditioning value of the sine and cosine signals are preloaded on-chip by factory. This will minimize mechanical sensor misalignment error. Features • Two Sine/Cosine true differential outputs with 1024 periods for unit alignment • Integrated highly collimated illumination system • 11 digital tracks plus 2 sin/cos tracks generate precise 16 bit Gray code • Ultra fast, 1µs cycle for serial data output word equals 16MHz • The 12 bits MSB is functionable up to 12000 RPM, 16 bit up to 1000RPM • MSB can be inverted for changing the counting direction • Monitor track for tracking the light level of the LED • Watch dog with alarm output pin LERR • -25 °C to + 85 °C operating temperature Benefits • No battery or capacitor required for position detection during power failure • Immediate position detection on power up Applications • Rotary application up to 16 bits / 360° absolute position • Cost effective solution for direct integration into OEM systems • Linear positioning system Signal-channels A1-A11 The photocurrent of the photodiodes is fed into a transimpedance amplifier. The analog output of the amplifier has a voltage swing of(dark/light) about 1.3V. Every output is transformed by precision comparators into digital signals (D1-D11). The threshold is at VDD/2(=Analog-reference), regulated by the monitor channel. LSB gray code Correction (Pin KORR) This function block synchronizes the switching points for the 11 bit gray code of the digital signals D1 to D11 with D0 and D09 (digitized signal of A0 and A09). The accuracy of the complete 12 bit gray is defined by the precision of the signals D0/D09. As these two signals are generated by the gain and offset conditioned analog signals A0 and A09, they are very precise. This Gray code correction only works for the full 12 bit (4096 steps per revolution). The correction is not for the 4 excess interpolated bits of the 16 bit Gray code. Gray code correction can be switched on or off by putting the pin KORR =1(on) or =0(off ). Monitor Channel with LED Control at pins LEDR and LERR The analog output signal of the monitor channel is regulated by the LED current. An external bipolar transistor(to be connected by user) sets this level to VDD/2 (control voltage at pin LEDR). Thus the signal swing of each output is symmetrical to VDD/2(=Analog-reference) The error bit at pin LERR is triggered if the Ve of the internal bipolar transistor is larger than VDD/2 MSBINV and DOUT pins The serial interface consists of a shift register. The most pin MSBINV. Signals Channels A0, A09 with signal conditioning and cali- significant bit, MSB(D11) will always be sent first to DOUT. The MSB can be inverted (change code direction) by using bration These two channels give out a sine and cosine wave, which are 90 degree phase shifted. These signals have amplitudes, which are almost constant due to the LED current monitoring. Due to amplifier mismatch and mechanical misalignment the signals have gain and offset errors. These errors are eliminated by an adaptive signal conditioning circuitry. The conditioning values are on-chip preprogrammed by factory. The analog output signals of A0 and A09 are supplied as true-differential voltage with a peak to peak value of 2.0V at the pins A09P, A09N, A0P, A0N. DIN and NSL pins The Serial input DIN allows the configuration as ring register for multiple transmissions or for cascading 2 or more encoders. DIN is the input of the shift register that shifts the data to DOUT. The NSL pin controls the shift register, to switch it between load (1) or shift(0) mode. Under load mode, DOUT will give the logic of the MSB, i.e. D11. Under shift mode (0), coupled with the SCL, the register will be clocked, and gives out the serial word output bit by bit. As the clock frequency can be up to 16 MHz, the transmission of the full 16 bit word can be done within 1 µs. Valid data of DOUT should be read when the SCL clock is low. Please refer to timing diagram Figure 4. Interpolator for Channels A0,A09 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 12Bit Gray code at 12000 RPM. The interpolated 16 bit Gray code can be used up to 1000RPM only. At more than 1000RPM, only the 12 bit Gray code from the MSB side can be used.  Package Dimensions C L Radial + Tangential+ Z+ Z− Notes: 1. 3rd Angle Projection 2. Dimensions are in millimeters 3. Unless specified otherwise, the tolerances are: XX. – ±0.5; XX.X – ±0.2; XX.XX – ±0.03 4. Note: Codewheel and readhead mounting tolerances for radial, tangential and Z gap are: Radial : ± 50 um Tangential : ± 40um Z Gap : ± 50um Figure 1. Package Dimensions Device Selection Guide 1 Part Number AEAS-7500-1GSG0 Resolution 16 bit Operating Temperature (°C) -25 to 85 Output SSI + 1024 Sine/Cosine Incremental Output Code Gray Code DC Supply Voltage (V) +4.5 to +5.5 Notes: 1. For other options of absolute encoder module, please refer to factory.  Absolute Maximum Ratings 1, 2 Parameter DC Supply Voltage Input Voltage Output Voltage Moisture Level (Non-Condensing) Operating Temperature Storage Temperature Symbol VD Vin Vout %RH TA TS Limits -0.3 to + 6.0 -0.3 to +VD +0.3 -0.5 to +VD +0.3 85 -25 to 85 - 40 to 100 Units V V V % °C °C Notes: 1. Stresses greater than those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. 2. Exposure to absolute maximum rating conditions for extended periods may affect reliability. Recommended Operating Condition Values Parameter DC Supply Voltage Operating Temperature Input High Level Input Low Level Symbol VD TA VIH VLH Min. + 4.5 - 25 0.7*VD 0 Typ. + 5.0 25 Max. +5.5 +85 VD 0.3*VD Units V °C V V Notes 1 Notes: 1. Voltage ripple of supply voltage, Vripple, should be within 100mVpp or less for improved accuracy. Electrical Characteristics Electrical Characteristics over Recommended Operating Range, typical at TA=25 °C and VD = 5V Values Parameter Total Operating Current Digital Input-Pull Down Current Digital Input-Pull Up Current Digital Ouput-H-Level Digital Ouput-L-Level SCL Clock Frequency Duty Cycle SCL Clock Accuracy within one revolution1, 2, 3 Symbol Itotal Ipd Ipu VOH VOL fSCL TLH Condition Min Typ. 25 Max Units mA -20 30 IOH = 2 mA IOL = - 2 mA VD -0.5 V 0 -5 160 VD 0.5 16 mA mA V V MHz TLH = H/(L+H) fSCL = 5MHz RPM =80 Vripple