A fully differential type using CP2296 replace traditional Class AB Audio Power Amplifie

Handheld media playback device in the multi-speaker audio power amplifier for the class AB amplifier, divided into traditional and fully differential structure of type two. Fully differential-type structure shows superior noise immunity, so are more and more users. This paper presents a fully differential type replace traditional Class AB amplifier solution.

Class AB speaker amplifier

Class AB audio power amplifier speaker for its mature technology, audio performance, application of simple and low prices

Advantage has been low-power audio amplifiers occupy the mainstream market. Handset speaker amplifier, the maximum output power of about 1W (8. Load), such a bridge-tied load amplifier mostly BTL output, that is, without coupling capacitors, the output can be connected directly with the speaker. Currently on the market BTL Class AB audio amplifier output mainly traditional architecture and fully differential two kinds.

Traditional architecture

Will be the same with the output VO + lead back after a inverting amplifier, inverting the output by VO-, together with the output as a BTL.

Fully differential-type structure (Full differential)

Fully symmetrical circuit architecture, the input stage, output stage is true differential circuit.

A fully differential type using CP2296 replace traditional Class AB Audio Power Amplifier

Figure 1 traditional Class AB amplifier

A fully differential type using CP2296 replace traditional Class AB Audio Power Amplifier

Figure 2 Class AB fully differential amplifier type

Phone audio noise

More and more cell phones with music player functionality, compared to other music devices, mobile applications on the audio amplifier has more stringent requirements, mainly because of mobile phone electromagnetic environment is complex, may produce a variety of audio noise, affect the user use.

Phone motherboard, display, camera, memory and other equipment, high-speed data lines, address lines criss-cross, plus all types of RF signal line, may interfere with the audio amplifier, audio amplifier, once picked up to such Zaosheng, After amplification it is possible to achieve the degree of the user can hear. On the other hand GSM phone communicate with the base station, according to the time slot allocated to send data, time slot interval frequency is 217Hz. As the RF power amplifier power launched in the moment, taken from a large battery current (peak current can Daan Pei-level), leading to power supply ripple greatly, this ripple interference (frequency of 217Hz or so) will be from into the audio amplifier and power supply are reflected in the output (in most applications, the audio amplifier is battery powered directly). If this power reaches a certain level of interference, the human ear will clearly aware of the "buzzing" noise, namely the so-called TDD Noise (TDMA time slot noise).
When the phone transmitting power level (PCL) is high, the RF power amplifier peak current drawn larger, resulting

Interference has become even more apparent. In some specific situations, "humming" noise might be heard more easily by users. Case 1: Customer select a prelude to the soothing music as ringtones and mobile phones at a higher PCL level (such as PCL = 5, GSM900), happens in a moment a call comes in, ring volume according to the largest player, because then the low tone loudness "buzzing" noise will be relatively obvious. Case 2: SMS beep when the sound is very short because it is easy to expose the background "hum" noise. Case 3: user in a quiet environment for hands-free calls, "buzzing" sound would become particularly evident in the sound caused by the user's offensive, severe and even affect the normal call!

Shape structural limitations for mobile phones, speakers may be placed at a distance close to the location of mobile phone antennas; or speaker audio amplifier is very far away from the middle by a long lead or FPC for connection; or phone PCB layout is too tight, not audio good wiring circuit protection, and noise suppression filter components placed. These are common in the actual product design may lead to restrictions on serious RF interference and increase a "buzzing" noise possibilities.

Fully differential-type structure provides excellent anti-jamming capability

Fully differential structure of the amplifier, with the phase from the input side and look into the RP side of the circuit is completely symmetrical, and therefore provides excellent CMRR, PSRR, Click-POP noise suppression. PSRR indicators reflect the amplifier power supply noise rejection of the traditional architecture of the AB class amplifiers typically-62dB PSRR, while the fully differential amplifier is very easy to achieve-80dB or better performance. Visible, fully differential amplifier to the RF noise rejection capability is superior to the traditional class AB amplifiers.

Structure using traditional class AB amplifier in the event of a product RF noise (interference bands may be GSM900, they may also DCS1800), does not change the route in the case, only by adjusting the external components of several PF-level capacitance capacitor components, it is difficult to restrain noise. So more and more users from the traditional class AB amplifier to switch to Class AB fully differential amplifier type. According to many users experience, if you use fully differential amplifier
Follow the usual rules of placement and routing the audio circuit, usually no longer need to worry about interference (including radio frequency interference) caused by a variety of audible noise. This greatly simplifies system design and reduce risk.

CP2296 compatible with the traditional structure of AB type amplifier

Kai Pan Microelectronics (Chiphomer) launched a series of fully differential class AB type amplifier products to meet different application requirements. CP2296 Kai Pan Microelectronics (Chiphomer) features fully differential class AB amplifier products based products, its PSRR up to-85dB. CP2296 offers CSP9 package, the package of products compatible replacement market, the mainstream traditional class AB power amplifier architecture. When the user of the traditional class AB amplifiers are not satisfied with the performance, there is a new option - CP2296, no need to redesign the PCB, you can enjoy the fully differential class AB amplifier type superior performance.

A fully differential type using CP2296 replace traditional Class AB Audio Power Amplifier

Figure 3 CP2296 excellent PSRR rejection

CP2290 Kai Pan Microelectronics (Chiphomer) designed for a conventional class AB amplifier architecture, is fully compatible with the mainstream market, manufacturers of similar products. CP2290 and CP2296 are given the following compatible design program, which also applies to other vendors with traditional architecture class AB amplifier design compatible products.

Differential input mode compatible design

When the sound source to provide differential signal, CP2290/96 work in differential input mode, according to Figure 4 to design the circuit.

When using the CP2296, it will map the two Rf resistor NC, (CP2296 has built-in feedback resistor 40Ω).

When using the CP2290, the resistance in figure 2 Department paste 20kΩ resistor Rf. When using the CP2290, the proposed fixed Rf is 20kΩ, to change the gain by adjusting the Ri. This will replace the CP2296 CP2290, the gain remains the same (no need to change Ri), the software volume settings can be compatible. Can be seen in this mode, it can be a direct replacement for CP2290 to CP2296, no need to redesign the PCB.
Design of single-ended input mode compatible

When the source can only provide single-ended signal, CP2290/96 work in single-ended input mode, according to Figure 5, electrical design

Road. Be noted that, even in single-ended input mode, the fully differential type is still able to provide than traditional Class AB amplifiers superior performance. When using the CP2296, it will map the RS, Rf two resistors NC. When using the CP2290, the Department in the diagram labeled 20kΩ resistor Rf, RS Department paste 0Ω resistor, at the same time with terminal IN + with the Department of Ri and Ci of two components NC (Figure 5, red circle Office). Ibid reasons, fixed Rf is 20kΩ, by adjusting the IN-side of the Ri to change the gain.

Can be seen in the single-ended input mode, the only increase in the original design of a CP2290 for selected electrical 0Ω

Resistance RS, can be realized CP2290 and CP2296-compatible design, the changes brought about by the very small.

A fully differential type using CP2296 replace traditional Class AB Audio Power Amplifier

Figure 5CP2296 compatible with conventional single-ended mode class AB design

Two operating modes from the above replacement scheme can be seen, CP2296 can be very Fangbian replacement Chuan Tong Lei AB amplifier products, the use of Jianrongtidai program is very simple, the impact on Gaidongjixiao (differential input mode, or even no change) , but it can easily allow users to switch from traditional AB class amplifier for the fully differential type Class AB amplifier.


I recommend that users use in the new project design type AB fully differential audio amplifier, because it provides superior

Anti-jamming performance, greatly reduces the possibility of there various types of radio frequency noise and reduce the design difficulty and risk. If, for other considerations, still need to use the traditional class AB audio amplifier. The author recommends careful analysis and evaluation of new products in all kinds of interference that may exist, especially in radio frequency interference. Where necessary, should be considered a fully differential amplifier and the conventional class AB design compatible programs (such as the article mentioned CP2296), to avoid risks.

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