M02139 Datasheet, PDF (3/18 Pages) M/A-COM Technology Solutions, Inc. – 1G/10G Gbps TIA with AGC and Rate Select

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
differential output voltage. The equations used for I_N (Input Referred Noise) and G_TIA (Transimpedance) are shown
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).
I_N = (Vout_RMS / G_TIA)
G_TIA = (Vout_PP/ I_input_PP), where:
I_N = Input referred noise in RMS
G_TIA = TIA small signal transimpedance
I_input_PP= p-p input current
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^-12.
Sensitivity = 10log {((S/N x I_N x (ER + 1)) / (2 x ρ x (ER – 1))) x 1000} dBm
Where:
Sensitivity = Input sensitivity expressed in average power
S/N = 14.1(for 10^-12 BER)
I_N = Input Referred Noise in RMS
ER = Extinction Ratio = 10 (typically)
ρ = Photodiode Responsivity = 0.9 (typically)
02139-DSH-001-D
Mindspeed Technologies^®
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