3

Rev. 5/14/03

SP8034A APC Amplifier with Integrated Photodetector

© Copyright 2003 Sipex Corporation

PIN DESCRIPTION

PIN NUMBER

NAME

FUNCTION

Supply Voltage

2

GAIN

GAIN Select

4

GND

Power Ground

Gain Adjust 1(Gain Select = LOW)

Gain Adjust 2 (Gain Select = HIGH)

Reference Voltage

Output Voltage

The SP8034A is an Automatic Power Control

(APC) circuit for pick-up head applications.

The part consists of a photo-detector that con-

verts the light (780nm or 650nm) into current,

and active circuitry (transimpedance amplifier

and buffer) to convert the current into voltage.

The overall transfer characteristics are therefore

represented by a Voltage per Watt curve.

There are three pins for gain adjust, using two

separate external resistors for two separate gain

modes. This allows different adjust for a DVD

and a CD mode.

The two resistors are each tied from the corre-

sponding RG pin (pin 5 or 6, depending on the

mode) to the common gain pin (pin 3).

The gain adjust is proportional to the external

resistance and is done by means of an analog

duplication circuit that translates the resistance

value in an active feedback circuit at the

transimpedance amplifier. The fact that the exter-

nal resistor is not in the signal path ensures a better

signal quality and immunity to the parasitic ca-

pacitance/inductance on the pins 3,5 and 6.

In dark condition, the output of the circuit will

2.3V). When light (650nm or 780nm) is re-

output swing is guaranteed to be at least 1.5V

output can swing at least as low as 0.5V (abso-

lute).

Figure 2. Sensitivity vs. Gain Resistor (Absolute)

Gain (dB)

Sensitivity (mV/mW)

Regain (

Ts(nS) 1%

BW (MHz)

Pin(uW)

+6

4

950

13

61

380

02

400

12

79

750

-3

1.4

250

11

87

1070

-6 *

1

150

10

93

1500

Table 1. Target Gain Set Points for the System.

Figure 3. System Bandwith versus Gain Resistor,

V

0.0

200

400

600

800

1.0K

100M

95.0M

90.0M

85.0M

80.0M

75.0M

70.0M

65.0M

60.0M

55.0M

50.0M

45.0M

THEORY OF OPERATION

* V

0

1000

1500

2000

2500

3000

3500

4000

4500

5000

0

100

200

300

400

500

600

700

800

900

1000

Gain Adjust Resistor (Ω)