Hình 6,41 cho thấy một sơ đồ đơn giản của giai đoạn GaAsFET VGA báo cáo trong [78]. Giai đoạn khác biệt này là một phần của một bộ khuếch đại AGC bốn giai đoạn, trong đó có một băng thông là 18 GHz và được thực hiện trong một công nghệ GaAsHFET 0,3 pm với các thiết bị chế độ nâng cao và sự suy giảm. | DRIVER SPECIFICATIONS 261 temperature and end-of-life conditions. A typical range seen in commercial and 10-Gb s drivers for uncooled lasers is IM 10. 100 mA. Similarly the bias current range must be large enough to cover the threshold current Ith of a high-threshold laser under high-temperature and end-of-life conditions. A typical range seen in commercial and 10-Gb s drivers for uncooled lasers is IB 0. 100mA. Output Voltage Range Laser Drivers Although the laser driver s primary function is to generate the laser current i its output voltage Vo also must be considered see Fig. a . The proper operation of the driver is guaranteed only if the output voltage stays in the permitted output voltage range also called the compliance voltage. If the output voltage becomes too small Vo . the laser driver typically produces large pulse-width distortions and jitter because its output transistors are pushed into saturation BIT or the linear regime FET . Furthermore the modulation and bias currents may drop below their programmed values. If the output voltage becomes too large Vo VO max. the output devices may break down. The output voltage range constrains the laser loads that can be driven. If the load causes a large voltage drop the lower limit may be violated. Conversely some AC coupling schemes use a pull-up inductor and require that the output voltage can swing above the supply voltage which may conflict with the upper limit of the voltage range. We discuss the impact of DC- and AC-coupled lasers on the output voltage in Section . A laser driver that can operate at a small output voltage also has the advantage that the supply voltage for the load and with it the power dissipation can be kept small. Typical Values. The minimum permissible output voltage of a laser driver relative to the negative supply voltage typically is in the range . V. The maximum permissible output voltage usually is in the vicinity of the .
