02139-DSH-001-D

Mindspeed Technologies

®

3

Mindspeed Proprietary and Confidential

1.0 Product Specification

1.1

Description of Key Specifications

1.1.1

Input Referred Noise

In the design of a Transimpedance Amplifier, the primary goal is to minimize the input referred noise of the

amplifier. This achieves the best S/N ratio for optimum bit error rate performance of the incoming optical data

stream. The noise performance of a TIA is a key specification for meeting the stringent optical sensitivity

requirement. In general, the input referred noise calculations for a TIA are identical to those in other conventional

amplifiers. The input referred noise can be determined from several methods. Traditionally at Mindspeed, TIA noise

is obtained from dividing the output RMS voltage noise of the TIA by the transimpedance. The small signal

transimpedance of the TIA can be calculated by applying a known p-p input current and then measuring the p-p

below. The TIA output RMS noise can be measured conveniently by using a wide band oscilloscope (or by using a

power meter and converting the noise power to noise voltage).

1.1.2

Optical Input Sensitivity

TIA input sensitivity can be calculated from the optical sensitivity equation directly based on the input referred

noise, photodiode responsivity and transmitter extinction ratio information. Note that the Signal to Noise (S/N) must

exceed 14.1 to achieve a system bit error rate (BER) of 1x10

Where:

Sensitivity = Input sensitivity expressed in average power

S/N = 14.1(for 10

ER = Extinction Ratio = 10 (typically)

ρ = Photodiode Responsivity = 0.9 (typically)