As with many sectors that are based on well-defined topologies, each can be shown to have its own strengths and weaknesses, while still remaining a valid choice for a particular application type.
For example, push-pull Class B amplifiers were designed to be more efficient than the foregoing Class A topology, but Class B suffered with linearity issues due to the way that they switched. This was then addressed in the later Class AB topology, which switched in the linear region of the transistor.
Moving into the digital domain, Class D amplifiers incorporated a train of PWM pulses that were filtered and boosted to produce a faithful signal. The main advantage of this approach was efficiencies that exceeded 90% at loads above 25% of full load and 50% at very light loads.
The most recent topology is Toshiba’s Class TB (Tied BTL) amplifier for which a patent is in progress. This approach matches the efficiency of Class D at low power levels and delivers a huge 80% saving over Class AB designs. This level of efficiency can have a marked impact on improving vehicle efficiency and, by running cooler, less thermal management is required allowing designs to be realised in a much smaller space.
Class TB has a similar Bill-of-Material (BoM) count as Class AB, yet comprises less than half the components of a comparable Class D amplifier. The low-pass filter present in all Class D amplifiers causes a roll-off at 20kHz. As there is no LC filter in Class TB, they reproduce linearly up to 120kHz, thereby delivering far superior sound than is possible with Class D.
Toshiba’s TCB701FNG audio power amplifier IC is based upon Class TB, delivering all of the benefits in a simple, easy-to-use integrated package.
Toshiba has created a detailed white paper looking at in-vehicle audio technology and the associated challenges. To download the white paper, please click here: