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. Due to the increased integration of mobile device chips, more and more chipsets have chosen single-ended connection as the output of the headset channel. The TPA6132A2 also provides differential and single-ended inverting amplifier connections. However, due to some applications, such as the need to cooperate with other playback devices, the output phase has strict requirements, so it is necessary to connect the TPA6132A2 with a positive single-ended amplifier connection. This article will discuss the connection method of the TPA6132A2 forward single-ended amplifier and the matters needing attention.
1. Introduction to TPA6132A2
TPA6132A2 is the DirectPath series stereo headphone amplifier launched by TI. Due to the integration of Charge Pump, which provides a negative power supply, it can output the output waveform of the reference ground without DC component, so that the amplifier no longer requires a large output DC blocking capacitor.
The TPA6132A2 is a fully differential headphone amplifier that provides extremely high common-mode rejection ratio and power supply rejection ratio, so it can achieve extremely low noise output levels.
For single-ended connections, you can simply ground INL + and INR +, and the input signal is connected by INL- and INR-. At this time, TPA6132A2 constitutes an inverting amplifier circuit, and the input DC bias is 0V, which is directly supplied by INL / R +, so it can save a pair of coupling capacitors and because the left and right channels of the headphones refer to each other during playback, they are inverted Keeps the two channels in the same direction. So in the manual of TPA6132A2, TPA6132A2 takes the inverting amplifier circuit as an example. In actual applications, there are some scenarios where there is a phase that is not independently referenced. At this time, the sound wave will have a certain cancellation phenomenon in space. Therefore, some designs, even if using headphones, also want to use the original phase of the DAC output. Therefore, this article discusses and provides the correct connection of the non-inverting amplifier.
2. The principle of TPA6132A2 normal phase amplifier
a. TPA6132A2 internal principle
The TPA6132 integrates the feedback network of the amplifier circuit. According to the configuration of the G0 and G1 pins, different feedback network resistances can be used to obtain different amplification factors. SGND is used to connect the FM inductor shared by the left and right channel grounds of the earphone, and is used to eliminate the interference caused by the return current of the left and right channels on the inductor impedance.
b. TPA6132A2 normal phase amplifier connection method
Because the headphones are too sensitive to the DC component of the amplifier, and HPVSS is not completely symmetrical to VBAT, it is necessary to introduce DC feedback to reduce the DC component of the output. Therefore, INL- and INR- need to be grounded through a DC feedback capacitor. Because the output of the front-end chip generally has a high DC component, it is necessary to connect a DC blocking capacitor at the INL + and INR + ends.
The impedance of the positive input pin and the inverting input pin are equal, so the DC blocking capacitor and DC feedback capacitor can choose the same capacity.
3. Precautions for use of normal phase single-ended amplifier
a. Selection of input capacitance and feedback capacitance and noise suppression
Because the input capacitance and feedback capacitance are included in the feedback network at low-frequency capacitive reactance, the mismatched capacitance will reduce the common-mode rejection ratio of the corresponding frequency band, so in practical applications, you can choose:
1. High-precision capacitors are used as input and feedback capacitors, so that the capacitive reactance can be greatly approached, reducing the impact on the common mode rejection ratio;
2. Capacitors with larger capacitances are used as input and feedback capacitors, so even if the capacitances of the two capacitors are different, since the capacitive reactance is lower than the feedback resistor network, it can also reduce the impact on the common mode rejection ratio.
b. Ground point of DC feedback capacitor
Due to the high degree of integration of mobile equipment, it is difficult to plan a strict ground return current, so the actual return wiring needs to consider the impact of the return current on the circuit. Generally, the analog ground point of the previous chip is selected as the ground point of the DC feedback capacitor. Because the input signal and feedback can refer to the same ground, the noise picked up on the ground line can be eliminated by the common mode suppression of the amplifier.
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