TI's TPA6132A2 is 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 high cost performance. Due to the increased integration of mobile device chips, more and more chipsets have chosen a single-ended connection as the output of the headphone channel. The TPA6132A2 provides both differential and single-ended inverting amplification connections. However, some applications, such as the need to use with other playback devices, have strict requirements on the phase of the output, so the TPA6132A2 needs to be connected in a forward single-ended amplifier. This article will discuss the connection method of the TPA6132A2's forward single-ended amplifier, as well as matters needing attention.
1. Introduction to TPA6132A2
The TPA6132A2 is TI's DirectPath series of stereo headphone amplifiers. With the integrated Charge Pump, it provides a negative power supply, so it can output a DC-free output waveform of the reference ground, so that the amplifier no longer needs a large output DC blocking capacitor.
The TPA6132A2 acts as a fully differential input headphone amplifier that provides a very high common-mode rejection ratio and power supply rejection ratio, resulting in extremely low noise output levels.
For single-ended connections, INL+ and INR+ can be simply grounded and the input signal is connected by INL- and INR-. At this time, the TPA6132A2 constitutes an inverting amplifying circuit. The input DC bias is 0V, which is directly supplied by INL/R+, so a pair of coupling capacitors can be saved and the left and right channels of the headphones are mutually referenced during playback, so they are simultaneously inverted. The two channels remain in the same direction. So in the TPA6132A2 manual, the TPA6132A2 uses an inverting amplifier circuit as an example. In actual applications, there are some scenes, and there are non-independent reference phases. At this time, the sound waves will have some offset in space. Therefore, some designs, even if headphones are used, hope to use the original phase of the DAC output. This article therefore discusses and provides the correct connection for a positive phase amplifier.
2.TPA6132A2 positive phase amplifier principle
a. Internal principle of TPA6132A2
The TPA6132 integrates the feedback network of the amplifying circuit. According to the configuration of the G0 and G1 pins, different feedback network resistance values ​​can be obtained to obtain different amplification factors. SGND is used to connect the FM inductor shared by the left and right channel grounding of the earphone to eliminate the interference caused by the grounding current of the left and right channels on the inductive impedance.
b.TPA6132A2 positive phase amplifier connection method
Because the headphone is 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 front-end chip output generally has a high DC component, it is necessary to connect the DC blocking capacitors at the INL+ and INR+ terminals.
The impedances of the positive input pin and the inverting input pin are equal, so the DC blocking capacitor and the DC feedback capacitor can select the same capacity.
3. Precautions for the use of positive phase single-ended amplifiers
a. Input capacitor and feedback capacitor selection and noise suppression
Because the input capacitance and feedback capacitance are accounted for in the feedback network at low frequency, the unmatched 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 close, reducing the influence on the common mode rejection ratio;
2. A larger capacity capacitor acts as an input and feedback capacitor, so that even if there is a difference in capacitance between the two capacitors, the effect on the common mode rejection ratio can be reduced because the capacitive reactance is lower relative to the feedback resistor network.
b. Grounding point of DC feedback capacitor
Due to the high integration of mobile devices, it is difficult to plan a strict return current, so in the actual wiring, it is necessary to consider the influence of the return current on the circuit. Generally, the analog ground point of the preamplifier is selected as the grounding point of the DC feedback capacitor. Since the input signal and the feedback can refer to the same ground, the noise picked up on the ground line can be eliminated by the amplifier common mode rejection.
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