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AD9660

PIN DESCRIPTIONS

Function

OUTPUT

Analog laser diode current output. Connect to anode of laser diode, cathode connected to GROUND externally.

BIAS LEVEL

Analog voltage input, VREF to VREF + 1.6 V. Bias current is set proportional to the BIAS LEVEL during calibra-

tion as follows:

MONITOR =

BIAS LEVEL − VREF

1.85

× R

GAIN + 50 Ω

()

BIAS CAL

TTL/CMOS compatible, Bias loop T/H control signal. Logic HIGH enables calibration mode, and the bias loop

T/H immediately goes into track mode. Logic LOW disables the bias loop T/H and immediately places it in hold

mode. WRITE PULSE should be held logic LOW while calibrating. Floats logic HIGH.

BIAS HOLD

External hold capacitor for the bias loop T/H. Approximate droop in the bias current while BIAS CAL is logic

LOW is: ±∆IBIAS =

×10

–9

BIAS HOLD

. Bandwidth of the loop is: BW =

π (550 Ω)C

BIAS HOLD

WRITE PULSE

TTL/CMOS compatible, current control signal. Logic HIGH supplies IMODULATION to the laser diode. Logic

LOW turns IMODULATION off. Floats logic HIGH.

WRITE CAL

TTL/CMOS compatible, write loop T/H control signal. Logic HIGH enables calibration mode; before enabling

calibration the bias loop should be calibrated and OFFSET PULSE driven to an appropriate state. In calibration

mode, 13 ns after the WRITE PULSE goes logic HIGH, the write loop T/H goes into track mode (there is no de-

lay if WRITE PULSE is HIGH before WRITE CAL transitions to a HIGH level). The write loop T/H immedi-

ately goes into hold mode when the WRITE PULSE goes Logic LOW. WRITE CAL LOW disables the write

loop T/H and places it in hold mode. Floats logic HIGH.

WRITE LEVEL

Analog voltage input, VREF to VREF +1.6 V. Write current is set proportional to the input voltage during calibra-

tion as follows: IMONITOR =

WRITE LEVEL − V REF

1.85

× (R

GAIN + 50 Ω)

WRITE HOLD

External hold capacitor for the write loop T/H. Approximate droop in IMODULATION current while WRITE CAL is

logic LOW is: ±∆IMODULATED =

×10

−9

WRITE HOLD

. Bandwidth of the loop is:

π (550 Ω) C

BIAS HOLD

SENSE IN

Analog current input, IMONITOR, from PIN photo detector diode. SENSE IN should be connected to the cathode

of the PIN diode, with the PIN anode connected to GROUND or a negative voltage. Voltage at SENSE IN var-

ies slightly with temperature and current, but is typically 4.0 V.

GAIN

External connection for the feedback network of the transimpedance amplifier. External feedback network, RGAIN

and CGAIN, should be connected between GAIN and POWER MONITOR. See text for choosing values.

POWER

Output voltage monitor of the internal feedback loop. Voltage is proportional to feedback current from photo

MONITOR

diode.

OFFSET

Set resistor connection for the offset current source. Resistor between OFFSET CURRENT SET and +VS

CURRENT SET determines offset current level. The input voltage at this node varies slightly with temperature and current, but is

typically 1.4 V. See curves. Can also be driven with a current out DAC.

OFFSET

TTL/CMOS compatible, OFFSET current control signal. Logic HIGH adds IOFFSET to IOUT. Logic LOW

PULSE

turns off IOFFSET. Floats logic HIGH.

DISABLE

TTL/CMOS compatible, current output disable circuit. Logic LOW for normal operation; logic HIGH disables

the current outputs to the laser diode, and drives the voltage on the hold capacitors close to VREF (minimizes the

output current when the device is re-enabled). DISABLE floats logic HIGH.

VREF

Analog Voltage Output, internal bandgap voltage reference, ~1.75 V, provided to user for power level offset.

+VS

Positive Power Supply. Nominally +5 V, pin connections should be tied together externally.

GROUND

Ground Reference. All grounds should be tied together externally.

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