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APPLICATION INFORMATION

FULLY DIFFERENTIAL AMPLIFIER

Advantages of Fully Differential Amplifiers

BOOST CONVERTER

Boost Terms

TPA2013D1

SLOS520 – AUGUST 2007

The TPA2013D1 is a fully differential amplifier with differential inputs and outputs. The fully differential amplifier

consists of a differential amplifier with common-mode feedback. The differential amplifier ensures that the

amplifier outputs a differential voltage on the output that is equal to the differential input times the gain. The

of the common-mode voltage at the input. The fully differential TPA2013D1 can still be used with a single-ended

input; however, the TPA2013D1 should be used with differential inputs when in a noisy environment, like a

wireless handset, to ensure maximum noise rejection.

• Input-coupling capacitors not required:

–

The fully differential amplifier allows the inputs to be biased at voltage other than mid-supply. The inputs of

the TPA2013D1 can be biased anywhere within the common mode input voltage range listed in the

Recommended Operating Conditions table. If the inputs are biased outside of that range, input-coupling

capacitors are required.

• Midsupply bypass capacitor, C

–

The fully differential amplifier does not require a bypass capacitor. Any shift in the midsupply affects both

positive and negative channels equally and cancels at the differential output.

• Better RF-immunity:

–

GSM handsets save power by turning on and shutting off the RF transmitter at a rate of 217 Hz. The

transmitted signal is picked-up on input and output traces. The fully differential amplifier cancels the signal

better than the typical audio amplifier.

The TPA2013D1 consists of a boost converter and a Class-D amplifier. The boost converter takes a low supply

The two main passive components necessary for the boost converter are the boost inductor and the boost

capacitor. The boost inductor stores current, and the boost capacitor stores charge. As the Class-D amplifier

depletes the charge in the boost capacitor, the boost inductor charges it back up with the stored current. The

The following is a list of terms and definitions used in the boost equations found later in this document.

C

L

Boost inductor

Switching frequency of the boost converter.

Current pulled by the Class-D amplifier from the boost converter.

Average current through the boost inductor.

R1 and R2

Resistors used to set the boost voltage.

Boost voltage. Generated by the boost converter. Voltage supply for the Class-D

amplifier.

Supply voltage to the IC.

Ripple current through the inductor.

ΔV

Copyright © 2007, Texas Instruments Incorporated

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