TPA6132A2 positive phase single-ended amplifier circuit design

The TPA6132A2 provided by TI has been widely used in mobile devices such as mobile phones because of its high signal-to-noise ratio of 100dB, low distortion of 0.01%, excellent ability to eliminate POP sound, and extremely high cost performance.

As the integration of mobile device chips increases, more and more chipsets choose single-ended connection as the output of the headphone channel.

TPA6132A2 provides both differential and single-ended inverting amplification connection methods. However, some applications, such as the need to be used with other playback devices, have strict requirements on the output phase, so it is necessary to connect TPA6132A2 in the forward single-ended amplifier connection method.

This article will discuss the connection method of the TPA6132A2 forward single-ended amplifier and the things that need to be paid attention to.

 

1.TPA6132A2 Introduction

TPA6132A2 is a stereo headphone amplifier from TI's DirectPath series. With its integrated Charge Pump, it provides a negative power supply and is therefore able to output a ground-referenced DC-free output waveform, eliminating the need for a large output DC-blocking capacitor.

As a fully differential input headphone amplifier, the TPA6132A2 provides extremely high common-mode rejection ratio and power supply rejection ratio, thus achieving extremely low noise output levels.

For single-ended connection, INL+ and INR+ can be simply grounded, and the input signal is connected through INL- and INR-. At this time, TPA6132A2 forms an inverting amplifier circuit, and the input DC bias is 0V, which is directly supplied by INL/R+, so a pair of coupling capacitors can be saved. And because the left and right channels of the headphones refer to each other during playback, the two channels that are inverted at the same time maintain the same direction. Therefore, in the manual of TPA6132A2, TPA6132A2 uses the inverting amplifier circuit as an example.

In actual applications, there are some scenarios where there is a non-independent reference phase. At this time, the sound waves will have a certain cancellation phenomenon in space. Therefore, some designs, even when using headphones, hope to use the original phase of the DAC output. Therefore, this article discusses and provides the correct connection method of the positive phase amplifier.

Figure 1: TPA6132A2 single-ended inverting amplifier

2. TPA6132A2 positive-phase amplifier principle

a. TPA6132A2 internal principle

TPA6132 integrates the feedback network of the amplifier circuit. According to the configuration of G0 and G1 pins, different feedback network resistance values ​​can be enabled to obtain different amplification factors. SGND is used to connect the FM inductor shared by the left and right channels of the headphones to eliminate the crosstalk caused by the left and right channel ground current on the inductor impedance.

Figure 2 TPA6132A2 internal feedback network structure

b.TPA6132A2 positive-phase amplifier connection method

Because the headphones are too sensitive to the DC component of the amplifier and HPVSS is not completely symmetrical with VBAT, DC feedback is needed to reduce the DC component of the output. Therefore, INL- and INR- need to be grounded through a DC feedback capacitor.

Since the output of the front-end chip generally has a high DC component, it is necessary to connect DC blocking capacitors to the INL+ and INR+ terminals.

Figure 3 TPA6132A2 single-ended positive-inverting amplifier

Since the impedance of the positive input pin and the negative input pin are equal, the DC blocking capacitor and the DC feedback capacitor can be selected with the same capacity, which is equal to: where fc is the system's corner frequency, which is generally less than 20Hz, and Rin can refer to the resistance value in the table below.

Table 1 Resistance of Rin at different gains

3. Notes on using a positive-phase single-ended amplifier

a. Selection of input capacitor and feedback capacitor and noise suppression

Because the capacitive reactance of the input capacitor and the feedback capacitor at low frequencies will be included in the feedback network, the mismatched capacitors will reduce the common-mode rejection
ratio of the corresponding frequency band. Therefore, in practical applications, you can choose:

1. Use high-precision capacitors as input and feedback capacitors, so that the capacitive reactance can be greatly close, reducing the impact on the common-mode rejection ratio;

2. Use capacitors with larger capacitance as input and feedback capacitors. Even if the capacitance of the two capacitors is different, the impact on the common-mode rejection ratio can be reduced because the capacitive reactance is lower than that of the feedback resistor network.

b. Grounding point of DC feedback capacitor

Due to the high integration of mobile devices, it is difficult to plan strict return current, so the impact of return current on the circuit needs to be considered in the actual wiring. Generally, the analog grounding point of the previous chip is selected as the grounding point of the DC feedback capacitor, because the input signal and feedback can refer to the same ground, so the noise picked up on the ground line can be eliminated by the common mode suppression of the amplifier.