Over time, the use model of portable device audio amplification circuits has been greatly developed. For example, when the main function of a cellular phone is simply to reproduce speech from a speaker close to the ear, the earpiece requires very little power. In addition, audio quality such as total harmonic distortion (THD), noise, and signal-to-noise ratio (SNR) are rarely considered.
Speech is generally composed of high crest factor, low duty cycle signals, so speech requires very low average power, and efficiency is not a concern. Since RF and display functions are a major part of the total power consumption of cellular phones, most efficiency issues involve non-audio electronic components.
But recently, cell phones and other portable electronics have integrated handsets, headphone speakers, and near-field speakers (for hands-free operation). In addition, reproducing music (MP3 files) and movie channels also impose a heavy burden on the audio channel. As a result, the power consumption of the audio channel is no longer a branch problem, but becomes the main channel for power leakage. Moreover, low-fidelity sound reproduction has become a thing of the past, and today's audio transmission requires a signal-to-noise ratio of 100 dB or more and a total harmonic distortion of less than 0.1%.
Headphone Amplifier
Acoustic audio power amplifiers are generally divided into two types of operation: headphone amplifiers (HPA) and speaker amplifiers (SPA). Headphone amplifiers must drive 32Ω or 16Ω speakers up to 30mW and maintain very high audio quality (typically 105dB SNR, 0.01% THD and 20kHz bandwidth). However, for headset applications, 30mW is a very high output power that is high enough to cause pain. Typical listening levels are between 100μW and 1mW.
Producing 30mW of power on a 32Ω load requires a peak signal swing of 1.4V, while also preparing an extra margin for the IR drop. Therefore, a supply voltage of ±1.8V is usually used to achieve an output power of 30mW.
A typical headphone cable consists of three: two for the left and right drive signals and the other for the common return ground. In addition, additional lines may need to be added for volume control, mute, or microphone output. In this configuration, the stereo headphone amplifier must have a single-ended output.
However, if the power supply uses a single voltage rail, this will result in a large DC offset problem. To avoid the use of large AC-coupling capacitors, most headphone amplifiers are powered by a separate power supply, which typically uses an on-chip inverter charge pump to generate a negative voltage rail.
Most headphone amplifiers use linear amplifiers (for example, variants of the A/B type of output stage) to achieve the high quality audio performance required by headphone amplifiers. The traditional A/B class amplifier consists of Class A and Class B operating modes. These amplifiers are typically designed to operate primarily in Class A at low output power. Class A states provide the best audio performance due to the low crossover distortion.
The Class B mode of operation is effective at high output levels, when it has higher efficiency than Class A. However, the Class B mode of operation has higher crossover distortion. In summary, Class A/B amplifiers can achieve very low total harmonic distortion because most of the crossover distortion can be attenuated by closed loop feedback.
Under constant supply conditions, the A/B class amplifier efficiency is proportional to the output voltage swing. In order to recover the efficiency loss at low output power, the "G-type operating mode" technique can be used to reduce the voltage rail value at low level signals.
A circuit is needed to detect the input signal level. If the level exceeds a predetermined threshold, the voltage rail can be raised to a higher value as needed. Most Class G amplifiers have two voltage rail values: one for the high rail value of the large signal swing (VDD) and one for the low level signal with only a small portion of VDD (such as 1/2 of VDD). Low track value. Thus, the signal efficiency at full scale output power 1/4 is approximately equal to the efficiency of the full scale power signal.
A variant of the Class G operating mode is named "Class H Operating Mode", in which case the power rail continuously changes as the peak signal is required. This maximizes the efficiency of all signal level points. However, due to circuit design and process limitations, the minimum voltage rail value for Class H operating modes is limited.
Some manufacturers apply the term "Class H" to actually operate on a Class G headphone amplifier. True Class H operating modes are rarely seen in current IC headphone amplifiers.
8 Inch Tablet
Today let`s talk about 8 inch tablet with android os or windows os. There are many 8 inch tablets on sale you can see at this store. 8 inch Android Tablet is absolutely the No. 1 choice if you are searching a student online learning project. 8 inch windows tablet is more welcome when clients are looking tablet for business application. The most welcome parameters level is 2 32Gb with 4GB lite, 4000mAh, android 11 only around 60usd, price will be much competitive if can take more than 1000pcs. 7 Inch Tablet wifi only, android tablet 10 inch, Amazon 8 inch tablet is also alternative here. Except tablet, Education Laptop, Gaming Laptop, 1650 graphics card laptop, Mini PC and All In One PC are the other important series.
Therefore, you just need to share the configuration, application scenarios, quantity, delivery time, and other special requirements, then will try our best to support you.
Any other thing in China we can do, you can also feel free to contact us.
You will find that cooperating with us is the best choice, not only save time and energy, but also save much cost.
8 Inch Tablet,8 Inch Android Tablet,Amazon 8 Inch Tablet,8 Inch Tablets On Sale,8 Inch Windows Tablet
Henan Shuyi Electronics Co., Ltd. , https://www.shuyipc.com