Published online by Cambridge University Press: 05 March 2013
What is a high-speed digital output driver?
High-speed digital output drivers can be regarded as very broadband, DC- or AC-coupled power amplifiers which operate in switching (or limiting) mode and transmit high-speed digital signals off chip to the outside world. In wireline applications, the output signal is sent into a 50Ω transmission line on a board, or to a coaxial cable. In fiber-optic systems, the signal (voltage or current, rather than power) from the output driver modulates the bias current of a laser diode or the bias voltage of an electro-optical modulator. As illustrated in Figure 12.1, the data input is typically differential and operates with signal levels in the 50mVpp to 1.5Vpp range, while the data output can be either differential or single-ended. In some standalone laser or modulator drivers, the data are retimed using an external clock input before being amplified and re-shaped.
Like tuned PAs, high-speed digital output drivers have widely varying requirements and typically impose the toughest demands on semiconductor technologies in terms of breakdown voltage and transistor speed. As a result, linear-mode operation is avoided because it is very costly and very difficult to accommodate.
There has been a growing trend towards introducing flexibility in the shape of the output signal. Control over the output waveform is often needed to overcome imperfections in the response of wireline channels or of optical devices such as lasers and modulators. Initially, because of power consumption constraints and bandwidth requirements, all waveshape control functions were realized with analog techniques.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.