Signal-channels A1-A11

The photocurrent of the photodiodes is fed into a tran-

simpedance amplifier. The analog output of the amplifier

hasavoltageswingof(dark/light)about1.3V. Everyoutput

istransformedbyprecisioncomparatorsintodigitalsignals

(D1-D11). The threshold is at VDD/2(=Analog-reference),

regulated by the monitor channel.

Monitor Channel with LED Control at pins LEDR and LERR

The analog output signal of the monitor channel is regu-

lated 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 theVe of the internal

bipolar transistor is larger than VDD/2

Signals Channels A0, A09 with signal conditioning and cali-

bration

Thesetwochannelsgiveoutasineandcosinewave,which

are90degreephaseshifted. Thesesignalshaveamplitudes,

whicharealmostconstantduetotheLEDcurrentmonitor-

ing. Due to amplifier mismatch and mechanical misalign-

ment the signals have gain and offset errors. These errors

areeliminatedbyanadaptivesignalconditioningcircuitry.

The conditioning values are on-chip preprogrammed by

factory. The analog output signals of A0 and A09 are sup-

plied as true-differential voltage with a peak to peak value

of 2.0V at the pins A09P, A09N, A0P, A0N.

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.

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

the16bitGraycode. Graycodecorrectioncanbeswitched

on or off by putting the pin KORR =1(on) or =0(off).

MSBINV and DOUT pins

The serial interface consists of a shift register. The most

significant bit, MSB(D11) will always be sent first to DOUT.

The MSB can be inverted (change code direction) by using

pin MSBINV.

DIN and NSL pins

The Serial input DIN allows the configuration as ring reg-

ister for multiple transmissions or for cascading 2 or more

encoders. DIN is the input of the shift register that shifts

the data to DOUT.

TheNSLpincontrolstheshiftregister,toswitchitbetween

load (1) or shift(0) mode. Under load mode, DOUT will give

the logic of the MSB, i.e. D11.

Undershiftmode(0),coupledwiththeSCL,theregisterwill

be clocked, and gives out the serial word output bit by bit.

As the clock frequency can be up to 16 MHz, the transmis-

sion 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.