How To Filter Audio Hum With Magnets
Solution Guide
Solution guide to the employ of noise suppression filters in audio lines – Outline
In the absence of any measures, electromagnetic dissonance is emitted from the wiring in smartphone speakers also equally the audio lines of headphones. Since this noise interferes with the built-in antenna and causes a drop in reception sensitivity, generally chip beads are inserted as a dissonance suppression measure out. However, even though chip beads are effective for noise suppression, they also have a problem considering they cause voice distortion when used for sound lines. As a solution for this problem, TDK has adult the MAF series of noise suppression filters for sound lines using a new production concept. Since these filters take an fantabulous noise attenuation effect in the cellular band, use of these filters results in corking improvement in reception sensitivity, and solves the problem of degradation in dissonance quality found in the parts which have been used and so far for noise suppression. They are extremely effective in reducing harmonic distortion in Form-D amplifiers which are existence used in smartphones.
Guide to the MAF series of dissonance suppression filters for audio lines
| Type ＼ Size L × W mm | 1005mm(0402inch) | 1608mm(0603inch) |
|---|---|---|
| G type (to ensure cellular reception sensitivity) | MAF1005G | MAF1608G |
| F type (to suppress harmonic distortion in Class-D amplifiers) | ― | MAF1608F |
1．Background of the development of the MAF serial of racket suppression filters for audio lines
Why is noise suppression of import for audio lines?
Figure 1 shows a block diagram of the audio lines in a smartphone. In a smartphone, a Course-D amplifier, which is a digital amplifier, is used as the power amplifier for the speakers. A Course-D amplifier is as well known as a switching amplifier, and information technology is a arrangement that uses PWM (pulse width modulation) applied science using switching elements (MOSFET, etc.) to convert audio input signals into pulse signals, and after amplifying them, reconverts them to analog signals and sends the output to the speakers. However, since pulse signals take many harmonic distortion components, in the absenteeism of cosmetic measures, the wiring connecting the Grade-D amplifier and the speakers becomes an antenna, causing electromagnetic noise emission, which interferes with the congenital-in antenna, and leads to deposition of reception sensitivity. In other words, it is the problem of "self-poisoning". A Form-D amplifier is compact and has excellent power efficiency, and it is used to amend the time for which the bombardment lasts, even if it is by a modest amount, in multi-functional devices with high ability consumption such as smartphones. This trouble of deposition of reception sensitivity also arises due to racket from the headphone line.
Further, noise suppression measures used so far in audio lines resulted in the problem of voice baloney caused by baloney in the audio signal waveform. With increasing interest in Hullo-Fi audio available in smartphones and headphones supporting "Hi-Res", it has become necessary to discover solutions to the problems of degradation of reception sensitivity and vocalisation distortion in audio lines.
Effigy 1: Block diagram of the sound lines in a smartphone, and the problems of "cocky-poisoning" and vocalization baloney
Problems when scrap beads are used for noise suppression
In order to suppress the noise emitted from sound lines, chip beads are by and large inserted in the output stage of Course-D amplifiers. These are chip components consisting of a coil inserted into a ferrite body using a lamination procedure. Chip bead impedance is expressed as the reactance component and AC resistance component of the gyre. In the low frequency region, it is mainly the reactance component which functions to reflect dissonance, and in the high frequency region, it is mainly the Air conditioning resistance component which functions to absorb noise and convert it into heat. It is the ferrite which largely determines the characteristics of the chip chaplet. In the power supply system through which large current flows, chip beads with a large Ac resistance component are used. Relatively large current also flows through the speaker lines in a smartphone. Withal, for chip chaplet which take a large AC resistance component, the vocalism distortion tends to increase, and in the existing scrap beads manufactured using ferrite, it was difficult to eliminate noise and simultaneously minimize the phonation baloney.
Noise suppression filter manufactured using TDK's proprietary low distortion ferrite material
Figure 2: Comparing of the characteristics of the MAF series of dissonance suppression filters with chip beads
In society to overcome the problems which are difficult to resolve when chip beads are used, we at TDK have used our accumulated fabric design engineering science to develop a new ferrite cloth which achieves low distortion while retaining its noise elimination characteristics. And, based on a new product concept, we have created multilayer chip components exclusively for noise suppression in the audio lines of devices such every bit smartphones. This is how the MAF series of noise suppression filters for audio lines was built-in. Incidentally, the name MAF is an acronym formed from the 3 words M (Multilayer), A (Hi-Fi Sound), and F (Noise suppression Filter).
Figure 2 shows a comparing of the characteristics of the MAF serial of racket suppression filters with chip chaplet. From this comparison, it is clear that the MAF series of dissonance suppression filters is a uniquely positioned product which combines the characteristics of first-class noise elimination and low distortion.
Product range consisting of the G type and F type optimized for various applications
The MAF series of noise suppression filters for sound lines from TDK is commercially available with the post-obit options: G type and F type in the 1608 size (L1.6 x W0.viii mm), and the G type in the 1005 size (L1.0 x W0.5 mm) (as of Baronial 2016). The G type is a product having high attenuation characteristics in major cellular bands (700MHz to 2GHz) such as LTE, and by inserting it into the speaker line and headphone line, the reception sensitivity can be considerably improved. The F type is for the speaker line, and when it is inserted in the output stage of a Course-D amplifier, it proves to be extremely effective in elimination of harmonic racket.
2．Guide for application to an audio line
1 Solution ①
Comeback in reception sensitivity and improvement in THD+N characteristics
The excellent features of the MAF series of noise suppression filters for audio lines are explained below with specific examples of their application. Effigy 3 is a block diagram showing the use of MAF1608F and MAF1608G in the speaker line, and the use of MAF1608G in the receiver (headphone/earphone) line.
Figure 3: Example of the use of /1608F in MAF1608G of the sound line in a smartphone
Starting time, the effect of using MAF1608G, which has high attenuation characteristics in the cellular band, is shown in Figure 4. The effigy shows the reception sensitivity - frequency characteristics:
◆When there is no filter
●When MAF1608G is inserted.
This is a measurement example of the 900MHz band. Compared to the example when there is no filter, the measurement reading shows an comeback which is as loftier equally 8dB when using MAF1608G. This is because, as y'all can conspicuously encounter from the insertion loss - frequency characteristics in Figure 5, the pattern has been optimized so that in this frequency ring, there is big insertion loss (＝ high impedance).
Figure 4: Result of insertion of MAF1608G into the speaker line (improvement in reception sensitivity) (1)
Reception sensitivity – Frequency characteristics
Effigy 5: Result of insertion of MAF1608G into the speaker line (comeback in reception sensitivity) (two)
Insertion loss – Frequency characteristics
Thus, it can be seen that the application of MAF1608G to audio lines is extremely effective as a solution to the problem of deposition of reception sensitivity in smartphones. Just what about the trouble of voice distortion acquired by insertion?
Voice distortion in audio lines is by and large expressed as a numeric value represented by THD+Due north (Total Harmonic Distortion + Noise). This is a ratio (Unit of measurement: [%]) representing the share of harmonic baloney and other noise components (Total Harmonic Distortion + Dissonance) in the source betoken component, and the lower this number, the better is the audio quality.
Figure 6: THD+N characteristics for MAF1608G
Effigy 6 is a graph which compares the THD+Due north characteristics versus the output of scrap chaplet (TDK MPZ1608D) and MAF1068G (Measured at a frequency of 1kHz, and load of RL=8Ω+33μF). Since the output with chip beads is around 200mW, the THD+North value of a sudden increases. On the other hand, even at an output of 1000mW, MAF1608G has most the same characteristics as when in that location is no filter. This means that even when it is inserted in the speaker line, it volition not cause voice distortions which is a problem in the case of chip chaplet. Also, the rated current of MAF1608G is as large every bit 1.6A, and information technology is platonic for speaker lines which require big current.
The DC resistance (RDC) is also an important characteristic. This is because, if the DC resistance is high, the ability consumption increases, and the signal level also drops. MAF1608G has accomplished a low resistance of 0.06Ω (typical value). As a result, the drib in sound volume due to insertion is pocket-sized, and it also contributes to a longer time for which the battery lasts.
two Solution ②
Application of MAF1608F to the speaker line
MAF1608F has even more than hitting THD+N characteristics. Effigy vii is a graph which compares the THD+Due north characteristics versus the output of fleck chaplet (TDK MPZ1608S) and MAF1068F (measured at a frequency of 1kHz, and load of RL=8Ω+33μF).
In case of the MPZ1608S chip beads, the THD+Northward value is stable at approximately 1[%], while the MAF1608F retains excellent characteristics until it approaches effectually 1000mW.
In MPZ1608S, Southward represents the ferrite material used, and S material is the standard type of material having frequency - impedance characteristics similar to ordinary ferrite.
The newly-adult low-distortion ferrite material used in the MAF series has contributed to extremely low THD+N characteristics, as tin be seen in the graph.
Figure eight shows the suppression issue of the racket emission from a Class-D amplifier by using MAF1608F. Since MAF1608F has been designed to show a high impedance value in the 100 to 400MHz frequency band, it is extremely constructive in racket suppression in this frequency band.
Figure 7: Issue of insertion of MAF1608F into the speaker line (1) Comparison of the THD + N characteristics versus output
Figure 8: Event of insertion of MAF1608F into the speaker line (two)
Upshot of suppression of racket emission in Class-D amplifiers past using MAF1608F
3 Solution ③
Application to headphone lines
Figure ix is an case of the application of MAF1005G for headphone lines. Figure x shows the comparison of the reception sensitivity with the instance when there is no filter in the 900MHz band (The last three digits in the product code represent the impedance). Compared to the case when there is no filter, there is an improvement of 6dB in the reception sensitivity.
Figure 9: Result of insertion of MAF1005G into the headphone line (1)
Effigy 10: Event of insertion of MAF1005G into the headphone line (two) Reception sensitivity – frequency characteristics
Figure eleven shows the THD+Due north value versus the output for the 1005 size (L1.0 x W0.5 mm) when compared to bit beads of the same size (TDK MMZ1005A). For scrap beads, 0.2mW is the limit, and increasing the output across this limit leads to a precipitous increment in the THD+N value. In other words, degradation of dissonance quality cannot exist avoided at high sound volume. On the other manus, MAF1005G has the same characteristics as when there is no filter fifty-fifty at a big output of several tens of mW.
Effigy 12 shows the FFT spectrum analysis of the THD+Northward characteristics versus output. In case of fleck chaplet, the harmonic baloney rises significantly at integral multiples of the measurement frequency (1kHz), and its THD+N value reaches 0.035%. On the other hand, in MAF1005G, the harmonic distortion is considerably suppressed, and the THD+N value is 0.00022%, which is almost zero.
Figure xi: THD+Northward characteristics for MAF1005G (1)
Comparison of the THD + N characteristics versus output
Figure 12: THD+Northward characteristics for MAF1005G (2)
Frequency spectrum analysis by an FFT analyzer
Summary
In mobile devices with communication functions such as smartphones and tablets, dissonance suppression components inserted into the audio lines of speakers, headphones/earphones, and microphones must meliorate reception sensitivity (by suppressing noise which is the cause of a drib in reception sensitivity) with minimal impact on the sound quality. The MAF serial of racket suppression filters for sound lines, which is a new product line from TDK, has high attenuation characteristics in the cellular band, and inserting information technology results in meaning improvement in the reception sensitivity. And, past using TDK's proprietary ferrite material with depression distortion, THD+N (Total harmonic distortion + Noise) , which is an indicator of voice distortion, is suppressed in the actual usage bandwidth until it is extremely close to zero, and this makes information technology an ideal noise suppression component for devices requiring high sound quality. They are too highly effective in reducing harmonic distortion in Class-D amplifiers which are being used in smartphones.
Thus, while the MAF series has excellent characteristics which cannot be implemented using fleck beads, in that location are also some points which tin can be handled using scrap beads in sound lines. Past appropriately using the MAF series of components in combination with chip beads, a diverseness of first-class solutions are offered non only for smartphones and tablets, but fifty-fifty for the audio lines of portable game consoles (Figure 13).
Figure thirteen: Recommended awarding of noise suppression components in a Hi-Fi audio line
《Master features and applications of the MAF series of noise suppression filters for sound lines》
【Main features】
- Compact noise suppression filters for audio lines and back up big current
- By using newly developed depression distortion ferrite material, there is considerable reduction in voice distortion during insertion into sound lines
- Since the resistance is depression, drop in audio book is small, and since they are able to suppress voice distortions, these filters are ideal for devices which require high audio quality
- Due to their high attenuation characteristics, they have proved to be highly constructive in suppressing degradation of reception sensitivity in the cellular band
【Main applications】
- Audio lines of smartphones and tablets (Speakers, headphones, microphone)
- Audio lines for portable game consoles
- Others
【MAF serial of noise suppression filters for audio lines】Product Data and Sample Buy
* Delight select the blazon/Part No. suitable for your applications to improve the reliability of your products.
Product Lineup: the MAF serial of noise suppression filters for audio lines (equally of August 2016)
| Function No. | Size [mm] | Impedance at 900MHz[Ω] typ. | DC resistance[Ω] typ. | Rated current [A] | THD+N[1W,1KHz]Resistor:8ohm | catalog |
|---|---|---|---|---|---|---|
| MAF1608GAD471C | 1608 | 470 | 0.06 | 1.6 | -86dB/0.005% | [157KB] |
| Part No. | Size [mm] | Impedance at 900MHz[Ω] typ. | DC resistance[Ω] typ. | Rated electric current [mA] | THD+N[10mW,1KHz]Resistor:32ohm | catalog |
|---|---|---|---|---|---|---|
| MAF1005GAD152A | 1005 | 1500 | 0.55 | 400 | -114dB/0.0002% | [178KB] |
| MAF1005GAD262A | 1005 | 2600 | ane.00 | 300 | -114dB/0.0002% | |
| MAF1005GAD352A | 1005 | 3500 | ane.30 | 270 | -114dB/0.0002% |
| Part No. | Size [mm] | Impedance at 100MHz[Ω] typ. | DC resistance[Ω] typ. | Rated current [A] | THD+N[1W,1KHz]Resistor:8ohm | catalog |
|---|---|---|---|---|---|---|
| MAF1608FAD121C | 1608 | 120 | 0.085 | ane.35 | -86dB/0.005% | [168KB] |
| MAF1608FAD151C | 1608 | 150 | 0.090 | 1.25 | -84dB/0.006% |
How To Filter Audio Hum With Magnets,
Source: https://product.tdk.com/en/techlibrary/solutionguide/suppression-filter_audio-line.html
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