PRELIMINARY DATA SHEET - Rev 2

08/2001

ATA01502

6

C

The C

path to a surface mount capacitor of at least 56pF

(additional capacitance can be added in parallel with

the 56 pF or 220 pF capacitors to improve low

frequency response and noise performance).

Referring to the equivalent circuit diagram and the

typical bonding diagram, it is critical that the

connection from C

bond wires for low inductance, since any high

frequency impedance at this node will be fed back to

the open loop amplifier with a resulting loss of

transimpedance bandwidth. Two pads are provided

for this purpose.

Sensitivity and Bandwidth

In order to guarantee sensitivity and bandwidth

performance, the TIA is subjected to a

comprehensive series of tests at the die sort level

performance and the high frequency performance

(i.e. adequate |S21|) of the amplifier. Acceptably high

|S21| of the internal gain stages will ensure low

amplifier input capacitance and hence low input

referred noise current. Transimpedance sensitivity

and bandwidth are then guaranteed by design and

correlation with RF and DC die sort test results. In

applications that require - 41 dBm sensitivity, a low

capacitance (< 0.5pF) and high responsitivity (> 0.95)

photodiode must be used.

Indirect Measurement of Optical Overload

Optical overload can be defined as the maximum

optical power above, which the BER (bit error rate)

ATA01502D1C is 100% tested at die sort by a DC

measurement, which has excellent correlation with

a PRBS optical overload measurement. The

measurement consists of sinking a negative current

(see V

the point of output voltage collapse. In addition, the

input node virtual ground during “heavy AGC” is

checked to verify that the linearity (i.e. pulse width

distortion) of the amplifier has not been

compromised. As a final test, a DC transfer curve is

performed on every die at the wafer level to ensure

excellent overload performance.

Measurement of Input Referred Noise Current

The “Input Noise Current” is directly related to

sensitivity. It can be defined as the output noise

voltage (V

MHz lowpass filter at the output of the TIA) divided by

the AC transresistance.

V

V

V

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

- 40

10

60

C

C

1

10

100

1000

Frequency (MHz)

8

7

6

5

4

3

2

1

1502

R

F

C

T

50

Ω

Figure 9: Input Offset Voltage vs. Temperature

Figure 10: Input Referred Noise Spectral Density