6.1.1 Predriver for External Class-D Amplifier

The external class-D amplifiers provide a stereo signal on terminals PreD.LEFT and PreD.RIGHT to drive the external class-D amplifier. These terminals are available if a stereo, single-ended, ac-coupled headset is used.

6.1.1.2 External Components and Application Schematics

Figure 6-2 is a simplified schematic for the external class-D predriver.

Input resistor (R_PR or R_PL) sets the gain of the external class D. For TPS2010D1, the gain is defined according to the following equation:

Gain (V/V) = 2*150*10³/(R_PR or R_PL)

R_PR or R_PL > 15 kΩ

Figure 6-2 Predriver for External Class D

NOTE

For other component values, see Table 5-48.

6.1.2 Vibrator H-Bridge

A digital signal from the pulse width modulated generator is fed to the vibrator H-bridge driver. The vibrator H-bridge is a differential driver that drives vibrator motors. The differential output allows dual rotation directions.

6.1.2.2 External Components and Application Schematics

Figure 6-3 is a simplified vibrator H-bridge schematic.

Figure 6-3 Vibrator H-Bridge

NOTE

For other component values, see Table 5-48.

Example of ferrite: BLM 18BD221SN1.

6.1.3 Carkit Output

The USB-CEA carkit uses the DP/DM pad to output audio signals (see the CEA-936–Mini-USB Analog Carkit specification).

Figure 6-4 shows the carkit output downlink full path characteristics for audio and USB.

Figure 6-4 Carkit Output Downlink Path Characteristics

Table 6-3 lists the USB-CEA carkit audio downlink electrical characteristics.

6.1.4 Digital Audio Filter Module

Figure 6-5 shows the digital audio filter downlink full path characteristics for the audio interface.

Figure 6-5 Digital Audio Filter Downlink Path Characteristics

The HPF can be bypassed. It is controlled by the MISC_SET_2 ARX_HPF_BYP bit set to address 0x49.

Table 6-4 lists the audio filter frequency responses relative to reference gain at 1 kHz.

6.1.5 Boost Stage

The boost effect adds emphasis to low frequencies. It compensates for a HPF created by the capacitor resistor (CR) filter of the headset (in ac-coupling configuration).

There are four modes. Three effects are available, with slightly different frequency responses, and the fourth setting disables the boost effect:

• Boost effect 1
• Boost effect 2
• Boost effect 3
• Flat equalization: The boost effect is in bypass mode.

Table 6-5 and Table 6-6 include the typical values according to the frequency response versus input frequency and F_S frequency.

6.2.1 Microphone Bias Module

A bias generator provides an external voltage of 2.2 V to bias the analog microphones (MICBIAS1 terminal). The typical output current is 1 mA.

6.2.1.1 Analog Microphone Bias Module Characteristics

Table 6-7 lists the characteristics of the analog microphone bias module.

Table 6-7 Analog Microphone Bias Module Characteristics With Bias Resistor

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNIT
Bias voltage		2.15	2.2	2.25	V
Load current				1	mA
Output noise	P-weighted 20 Hz to 6.6 kHz			1.8	μVRMS
External capacitor		0		200	pF
Internal resistance		50	60	70	kΩ

NOTE

If the external capacitor is higher than 200 pF, the analog microphone bias becomes unstable. To stabilize it, add a serial resistor.

Table 6-8 lists the characteristics of the analog microphone bias module with a bias resistor.

Table 6-8 Analog Microphone Bias Module Characteristics With Bias Resistor

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNIT
RSB	CB < 200 pF	0			Ω
	CB = 100 pF	300
	CB = 1 μF	500
RB + RSB			2.2 to 2.7		kΩ

Figure 6-6 and Figure 6-7 show the external components and application schematics for the analog microphone.

Figure 6-6 Analog Microphone Pseudodifferential

NOTE

For other component values, see Table 5-48.

Figure 6-7 Analog Microphone Differential

NOTE

For other component values, see Table 5-48.

NOTE

To improve the rejection, ensure that MICBIAS_GND is as clean as possible. This ground must be shared with AGND of the TPS65920 or TPS65930 device and must not share with AVSS4, which is the ground used by RX class AB output stages.

In differential mode, adding a low-pass filter (made by R_SB and C_B) is highly recommended if coupling between RX output stages and the microphone is too high (and not enough attenuation by the echo cancellation algorithm). The coupling can come from:

• The internal TPS65920/TPS65930 coupling between MICBIAS.OUT voltage and RX output stages
• Coupling noise between MICBIAS.GND and AVSS4

In pseudodifferential mode, the dynamic resistance of the microphone improves the rejection versus MICBIAS.OUT:

PSRR = 20*log((R_B + R_{Dyn_mic})/R_B).

6.2.1.2 Silicon Microphone Module Characteristics

Based on silicon micro-electrical-mechanical system (MEMS) technology, the new microphone achieves the same acoustic and electrical properties as conventional microphones, but is more rugged and exhibits higher heat resistance. These properties offer designers of a wide range of products greater flexibility and new opportunities to integrate microphones.

The silicon microphone is the integration of mechanical elements and electronics on a common silicon substrate through microfabrication technology.

The complementary metal oxide semiconductor (CMOS) MEMS microphone is more like an analog IC than a classical microphone, or electric condenser microphone (ECM). It is powered as an IC with a direct connection to the power supply. The on-chip isolation between the power input and the rest of the system adds power supply rejection (PSR) to the component. This makes the CMOS MEMS microphone inherently more immune to power supply noise than an ECM and eliminates the need for additional filtering circuitry to keep the power supply line clean.

Table 6-9 lists the characteristics of the silicon microphone module.

Table 6-9 Silicon Microphone Module Characteristics

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNIT
Bias voltage			2.2		V
Load current				1	mA
Output noise	P-weighted 20 Hz to 6.6 kHz			1.8	μVRMS

Figure 6-8 is a schematic for the silicon microphone.

Figure 6-8 Silicon Microphone

NOTE

For other component values, see Table 5-48.

6.2.2 FM Radio/Auxiliary Input

The auxiliary input AUXR/FMR can be used as FM radio input. The amplification stage output is connected to the ADC input. The FM radio input can also be output through an audio output stage.

6.2.2.1 External Components

Figure 6-9 shows the external components on the auxiliary input.

Figure 6-9 Audio Auxiliary Input

NOTE

For other component values, see Table 5-48.

6.2.3 Uplink Characteristics

Figure 6-10 shows the uplink amplifier. Table 6-10 lists the uplink characteristics.

Figure 6-10 Uplink Amplifier

6.2.4 Microphone Amplification Stage

The microphone amplification stages perform the single-to-differential conversion for single-ended inputs. Two programmable gains from 0 dB to 30 dB can be set:

• Automatic level control for main microphone input. The gain step is 1 dB.
• Level control by register for line-in or carkit input. The gain step is 6 dB.

The amplification stage outputs are connected to the ADC input (ADC left and right).

6.2.5 Carkit Input

The USB-CEA carkit uses the DP pad to input the audio signal.

Figure 6-11 shows the uplink carkit full path uplink characteristics for audio and USB.

Figure 6-11 Carkit Input Uplink Path Characteristics

Table 6-11 lists the USB-CEA carkit audio electrical characteristics.

6.2.6 Digital Audio Filter Module

Figure 6-12 shows the digital audio filter uplink full path characteristics for the audio interface.

Figure 6-12 Digital Audio Filter Uplink Path Characteristics

The high-pass filter (HPF) can be bypassed. It is controlled by the MISC_SET_2 ATX_HPF_BYP bit set to address 0x49.

Table 6-12 lists the audio filter frequency responses relative to reference gain at 1 kHz.