8/16

● Ci

This is a DC cut-off input coupling capacitor for the amp input pin.

This includes an Ri and a high-pass filter.

The cut-off frequency is calculated as follows.

[Hz]

Capacitors of a certain size are required for coupling without attenuation of low frequencies, but in most cases

of speakers used in portable equipment, it is nearly impossible to reproduce signals in the 100 to 200 Hz range or

below.

Even when a larger capacitor is used instead, it may not improve system performance.

Also, pop sounds can affect the capacitance (Ci) of the capacitor.

A larger coupling capacitor requires a greater charge to reach the bias DC voltage (normally 1/2 VCC).

Because this charge current is supplied from the output due to routing of feedback, pop sounds occur easily at

startup.

Consequently, pop sounds can be minimized by selecting the smallest capacitor that still has the required

low-frequency response.

● Ri

This is inverting input resistance, which sets the closed loop gain in conjunction with Rf.

● Rf

This is feedback resistance, which sets closed loop gain in conjunction with Rf.

The amp gain is set using the

following formula.

Gain = 20log

[dB]

● Cf

This is a feedback capacitor, which is used to cut high frequencies.

This includes Rf and a low-pass filter.

The cut-off frequency is calculated as follows.

[Hz]

1

2π×Ri×Ci

Ci-Frequency characteristic

-10

-8

-6

-4

-2

0

2

4

10

100

1k

10k

100k

Frequency[Hz]

Ci:0.22uF

Ci:0.1uF

Ci:0.047uF

Ci – Low Frequency Characteristics

Rf

Ri

1

2π×Ri×Ci