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Application NoteAnalog Microphone and ADC System in Far-field
ApplicationSungjin Max Roh
ABSTRACTFar-field audio applications such as AI speakers and sound bars, AI TVs, and other voice-activated products
need the following:•••••

Wide DR (Dynamic Range)
High AOP (Acoustic Overload Point)
Low THD (Total Harmonic Distortion) even for very loud signal
Low equivalent input noise
Small form factor with low power consumption

All of these electrical specifications have led to the voice commander getting precise voice command recognition
without any unexpected errors. This application report discusses and shows the benefits and strengths of analog
microphones with Texas Instruments TLV320ADC51x0/PCM51x0-Q1 system in far-field audio application.

Table of Contents
1 Near-Field and Far-Field.........................................................................................................................................................2
1.1 Definition............................................................................................................................................................................ 22 Constituents in the Far-Field Application.............................................................................................................................23 Understanding of Digital and Analog Microphone.............................................................................................................. 3
3.1 Digital PDM Microphone System....................................................................................................................................... 3
3.2 Analog Microphone with ADC System............................................................................................................................... 34 Quantization Noise Density for Each Microphone...............................................................................................................45 Dynamic Range in Far-Field...................................................................................................................................................5
5.1 DR...................................................................................................................................................................................... 5
5.2 DR in Microphone.............................................................................................................................................................. 5
5.3 DRE in the TLV320ADC5140/PCM5140-Q1...................................................................................................................... 5
5.4 DRE Performance in TLV320ADC5140/PCM5140-Q1...................................................................................................... 66 Design of Any Microphone with the TLV320ADC51x0/PCM51x0-Q1................................................................................. 7
6.1 Structure of the TLV320ADC51x0/PCM51x0-Q1............................................................................................................... 77 Conclusion.............................................................................................................................................................................. 98 Revision History......................................................................................................................................................................9Trademarks
All trademarks are the property of their respective owners.

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Near-Field and Far-Field

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1 Near-Field and Far-Field
1.1 Definition
Near-field and far-field are components of the physical distance from the sound source, as shown in Figure 1-1.
It depends on how far away a listener is from the sound-projecting object. At different distances, the acoustic
energy the wavelength emits is heard differently. It is a major issue to comprehend these differences and design
measurements precisely. Figure 1-1 implies that up to the second wave length is near-field, while from thesecond wave length is a range of far-field.

SoundSource

Near Field
0 ~ 2 wavelength

Far Field
2 wavelength ~ infinity

Figure 1-1. Near-Field and Far-Field from Sound Source
The essential idea within the range of a far-field is that 6 dB of sound pressure decreases for each doublingof distance away from the sound source. For the most of the voice recognition system, the commander stands
within the range of a far-field.

2 Constituents in the Far-Field Application
For a more accurate voice-activated system, far-field applications must obtain these elements, especially whenused for a voice recognition application.
Table 2-1 explains constituents that must be used for a better voice recognition system.
Table 2-1. Constituents of Far-field Application
APPLICATION NEEDED••2

SYSTEM SPECIFICATION NEEDEDCrystal clear
Distortion-free for audio capture

Wide dynamic range microphone and ADC

Microphone close to speakers in loud, noisy environments••

High AOP (Acoustic Overload Point)
Low THD (Total Harmonic Distortion even for very loud signal)

Far-field recording

Low EIN (Equivalent Input Noise)

Portability••

Small form factor
Low power consumption

Analog Microphone and ADC System in Far-field Application
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Understanding of Digital and Analog Microphone

3 Understanding of Digital and Analog Microphone
A microphone is a kind of transducer that converts sound pressure into electrical signal. There are two kinds ofmicrophones in collection with the sound waves. One of them is digital type, and the other is known as analog
type. This section contains the representing format of microphones, a digital PDM (Pulse Density Modulation)
microphone, and an analog microphone with ADC.

3.1 Digital PDM Microphone System
A digital PDM microphone works 1-bit stream as output with the direct output of the Sigma-delta modulator.
The sample rate of the PDM is typically between a few hundred kHz to 3.072 MHz. This Sigma-delta modulator
needs a decimation filter so that the PDM data can process further. The decimation filter is implanted in either
the codec, or the DSP where the PDM microphone is connected. This output from the filter sends out data ata lower sample rate of 16 and 48 kHz. This is a weaker point than an analog microphone with an ADC system
shown in Section 3.2. However, a PDM microphone does have some advantages over an I2S microphone. The
PDM microphone typically requires only two signal lines (PDM clock and PDM data) for audio interface, while
I2S requires three or four lines (bit clock, word clock, audio data, and occasionally master clock). This leads to abeneficial idea where the hardware engineers are easily able to minimize the physical interface line.

Modulator Clock3.072 MHz

MIC

1-bit
ADC

PGA

1-bit
PDMOutputPDMInterface

Figure 3-1. Digital PDM Microphone for 1-bit Output

3.2 Analog Microphone with ADC System
An analog microphone with an ADC system based on Texas Instruments’ TLV320ADC51x0/PCM51x0-Q1 uses
multi-bit modulation ADC to project audio data with a range higher than 24-bit, along with I2S (or PCM, TDM,DSP) interface, as shown in Figure 3-2. This is unlike the PDM microphone, which uses the 1-bit modulation
with PDM interface. For the analog microphone with ADC to project as shown in Figure 3-2, the I2S audio
signal of ADC output requires one or two more interface lines than the two of the PDM signals. The analog
microphone has advantages in in-band (20 Hz to 20 KHz) and out-of-band (above 20 KHz) for quantization noisecharacteristics (further explained in Section 4). This is because while the digital PDM microphone uses a 1-bit
ADC modulator with a 3.072 MHz clock, an analog microphone with ADC (Texas Instruments’ TLV320ADC51x0/
PCM51x0-Q1) uses multi-bit architecture with a modulator clock of 6.144 MHz, which allows it to have superior
qualities in quantization noise density.
Modulator Clock6.144 MHzDRE

MICPGA

Multi-bit
ADC

DigitalFilters> 24-bits
I2S/PCM/
TDM/DSPOutput

Figure 3-2. Analog Microphone with ADC for Multi-bit Output

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Quantization Noise Density for Each Microphone

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4 Quantization Noise Density for Each Microphone
The 1-bit modulator in the digital PDM microphone has architecturally high quantization noise that limits the PDM
microphone SNR and dynamic range compared to what can be achieved with an analog microphone along withmulti-bit ADC. The TLV320ADC51x0/PCM51x0-Q1 uses a multi-bit modulator which has in-band quantizationnoise up to 15 times lower, and better, than the typical 1-bit modulator. Moreover, the total quantization noiseof the TLV320ADC51x0/PCM51x0-Q1 multi-bit modulator is 30 times lower than the total typical quantizationnoise of a 1-bit PDM modulator. The high quantization noise in in-band has worse voice recognition, and every
6 dB improvement in microphone and system performance can be improved by the record distance and doubledsensitivity.
The higher total quantization noise of a 1-bit PDM modulator drastically limits the maximum high amplitude
signal that it can record with low distortion compared to a multi-bit ADC. This limitation makes the digital
microphone the incorrect choice to be used for sound bars, HDTVs, professional speakers, and so forth, where
the microphone is required to record very loud speaker output with low distortion so that the echo cancellation
can be achieved with good quality, and voice command detection successfully is enabled.
Figure 4-1 shows the typical quantization noise density difference in all bands for the 1-bit PDM modulator andmulti-bit analog modulator.

Figure 4-1. Quantization Noise Density

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Dynamic Range in Far-Field

5 Dynamic Range in Far-Field
5.1 DR
Dynamic range (also defined as DR, DNR, or DYR) describes the ratio between the level at which the greatest
sound converted with very low distortion to the softest sound in the system. In other words, the audio fielduses dynamic range to depict the ratio of the softest sound to the loudest sound level in the musical instrumentsystem. Therefore, dynamic range works as the SNR (Signal-to-Noise Ratio) for the case when the signal is theloudest possible in the system.

5.2 DR in Microphone
As shown in Section 5.1 for dynamic range, better SNR, lower THD (Total Harmonic Distortion), and better
AOP (Acoustic Overload Point) create high dynamic range. Here, AOP is the point at which the microphone
can record the loud sound with distortion as high as 10%. The microphone equivalent input noise (EIN) is used
to define microphone SNR to the point at which the microphone no longer effectively projects the difference
between the actual sound signal level and microphone self-noise level. It no longer works effectively as a soundpressure sensor at this point.

5.3 DRE in the TLV320ADC5140/PCM5140-Q1
The TLV320ADC5140/PCM5140-Q1 device integrates an ultra-low noise front-end PGA with 120 dB dynamic
range performance with a low noise, low-distortion, multi-bit delta-sigma (ΔΣ) ADC with a 108 dB dynamicrange. The dynamic range enhancer (DRE) is a digitally assisted algorithm to boost the overall channelperformance. The DRE monitors the incoming signal amplitude and adjusts the internal PGA gain accordingly
and automatically. The DRE achieves a complete channel dynamic range as high as 120 dB. At a systemlevel, the DRE scheme enables far-field, high-fidelity recording of audio signals in very quiet environments, andlow-distortion recording in loud environments. This algorithm is implemented with very low latency (a few µs looptime), and all signal chain blocks are designed to minimize any audible artifacts that can occur resulting fromdynamic gain modulation.
The block diagram in Figure 5-1 describes the complete signal chain performance with a high-performance
analog microphone.
As shown in Figure 5-1, if the system uses the high performance analog microphone with effective dynamic
range performance as high as 114 dB, along with a low-cost, 108 dB ADC without DRE, then the overall signal
chain dynamic range gets limited to 106.8 dB (114 dB–7.20 dB) due to the 108 dB ADC. However, once the DRE
scheme of the TLV320ADC5140 is enabled, an overall signal chain dynamic range of 112.97 dB (114dB–1.03dB)
can be achieved in a very economical manner, even after using a low-cost, 108 dB ADC.
Mic SNR = 70 dB
Mic 1% THD = 138dBSPL
Mic DR = 114 dB wrt
2Vrms
Mic o/p noise = 4 µVrms

PGA SNR = 120 dB wrt
2Vrms
PGA Gain = 0 dB
PGA i/p referred noise =2 µVrms

Mic + PGA noise =4.46 µVrms

ADC SNR = 108 dB wrt
2 Vrms
ADC noise = 7.96 µVrms

Mic + PGA + ADC noise =9.12 µVrms

Digital Gain = 0 dB
Final o/p noise = 9.12 µVrms
SNR degradation = -7.20 dB

V2 n-PGA_IN™¨Modulator

MIC
V2 n-Mic

DigitalFilters

PGADREPGA SNR = 120 dB wrt
2Vrms
PGA Gain = 24 dB
PGA i/p referred noise =2 µVrms

Mic + PGA noise =70.61 µVrms

ADC SNR = 108 dB wrt
2 Vrms
ADC noise = 7.96 µVrms

Mic + PGA + ADC noise =71.06 µVrms

Digital Gain = -24 dBFinal o/p noise =4.48 µVrms
SNR degradation = -1.03 dB

Figure 5-1. DRE Block Diagram

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Dynamic Range in Far-Field

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5.4 DRE Performance in TLV320ADC5140/PCM5140-Q1
Figure 5-2 and Figure 5-3 show the THD+N measurement results with and without DRE. The measurement
graph with DRE enabled (DRE threshold set to -36 dB) shows DR improvement of 12 dB and it also improves
the record distance and sensitivity by four times.
-60-70Channel-1 : DRE enabled
Channel-2 : DRE enabled
Channel-3 : DRE enabled
Channel-4 : DRE enabled

THD+N (dBFS)-80-90-100-110-120-130-130-115-100-85-70-55-40-25-10

Input Amplitude (dB)0
THD+Figure 5-2. THD+N Performance Measurement with DRE Enabled-60-70Channel-1 : DRE disabled
Channel-2 : DRE disabled
Channel-3 : DRE disabled
Channel-4 : DRE disabled

THD+N (dBFS)-80-90-100-110-120-130-130-115-100-85-70-55-40-25-10

Input Amplitude (dB)

0THD+Figure 5-3. THD+N Performance Measurement with DRE Disabled

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Design of Any Microphone with the TLV320ADC51x0/PCM51x0-Q1

6 Design of Any Microphone with the TLV320ADC51x0/PCM51x0-Q1
6.1 Structure of the TLV320ADC51x0/PCM51x0-Q1
Texas Instruments’ TLV320ADC51x0/PCM51x0-Q1 is four analog microphones, eight digital microphones, ora combination of both that an audio analog-to-digital converter can design as the input with four internal
Sigma-delta ADCs and eight digital microphone interfaces. This enables the hardware designer to have accessto flexible design structures, especially supporting the microphone array design.

GPIO18-channel Digital Microphone Filters

Multifunction Pins
(Digital Microphones Interface,Interrupt, PLL Input Clock)

IN1P_GPI1
IN1M_GPO1

ADC
Channel-1

PGA

IN1P_GPI2

PGA

ADC
Channel-2

IN1P_GPI3
IN1M_GPO3PGA

ADC
Channel-3

IN1P_GPI4
IN1M_GPO4PGA

ADC
Channel-4

IN1M_GPO2MICBIAS

Programmable
Microphone Bias

Audio Clock Generation
PLL(Input Clock Source ± BCLK,GPIOx, GPIx)

SDOUT
Digital Filters(Low Latency LPF
ProgrammableBiquads)

Audio SerialInterface(TDM, I2S, LJ)

andBCLK

Dynamic Range
Enhancer (DRE)FSYNC

I2C or SPI
ControlInterface

Regulators, Current Bias andVoltage Reference

SHDNZ

SDA_SSZ

SCL_MOSIADDR0_SCLKADDR1_MISO

IOVDD

Thermal Pad (VSS)

DREG

AREG

AVSS

AVDD

VREF

Figure 6-1. Internal Block Diagram of the TLV320ADC5140/PCM51x0-Q1
6.1.1 Design Example 1: Only Analog Microphone System
A differential analog microphone can be formed up to four multi-channels. In this case, the output signal changes
the front-end PGA into gain control, then uses high-performance, multi-bit sigma-delta AD to be converted byADC. After this process, it is sent to the decimation filter.

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Design of Any Microphone with the TLV320ADC51x0/PCM51x0-Q1

GPIO1

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8-channel Digital
Microphone Filters

Multifunction Pins
(Digital Microphones Interface,Interrupt, PLL Input Clock)

PGA

ADC
Channel-1

PGA

ADC
Channel-2

PGA

ADC
Channel-3

PGA

ADC
Channel-4

Figure 6-2. Analog Microphones System Block Diagram
6.1.2 Design Example 2: Only Digital Microphone System
The digital PDM microphone can be formed up to eight multi-channels. In this case, the PDM output from themicrophone goes through PDM interface to be sent to the decimation filter.

GPIO18-channel Digital
Microphone Filters

Multifunction Pins(Digital Microphones Interface,Interrupt, PLL Input Clock)

PDM mic
PDM mic

PGAADC
Channel-1

PDM mic
PDM mic

PGA

ADC
Channel-2

PDM mic
PDM mic

PGA

ADC
Channel-3

PDM mic
PDM mic

PGA

ADC
Channel-4

Figure 6-3. Digital PDM Microphones System Block Diagram
6.1.3 Design Example 3: Analog and Digital Microphone Combination System
The system can be formed as desired with analog and digital PDM microphones combined. In this case, each
input goes through design example 1 and 2, and is gradually sent to the decimation filter.

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Conclusion

GPIO18-channel Digital
Microphone Filters

Multifunction Pins
(Digital Microphones Interface,Interrupt, PLL Input Clock)

PGA

ADC
Channel-1

PGA

ADC
Channel-2

PDM mic
PDM mic

PGA

ADC
Channel-3

PDM mic
PDM mic

PGA

ADC
Channel-4

Figure 6-4. Combination Microphones System Block Diagram

7 Conclusion
By using the advantages of the analog microphones with Texas Instruments’ TLV320ADC51x0/PCM51x0-Q1system that brings in the far-field application, quantization noise density due to the modulation improves, whichbrings up the height to the DR system. This leads to the near perfection of the voice recognition system that
far-field application requires. The TLV320ADC51x0/PCM51x0-Q1 is an analog or digital microphone input used
for an audio analog-to-digital converter that can be designed to be accommodated as needed.

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9Revision History

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8 Revision History
Changes from Revision A (May 2022) to Revision B (December 2023)
Page• Added PCM51x0-Q1 throughout the document................................................................................................. 1
Changes from Revision * (June 2019) to Revision A (May 2022)
Page• Updated the numbering format for tables, figures, and cross-references throughout the document................. 2

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