Note:

In case FCL is kept the same for calculation, It must be taken in account that the 1st order high-pass filter on the

input and the 1st order high-pass filter on the output create a 2nd order high-pass filter in the audio signal path

with an attenuation 6 dB on FCL and a roll-off 40 db⁄ decade.

5.4

Higher cut-off frequency

In the high-frequency region, you can limit the bandwidth by adding a capacitor Cfeed in parallel with Rfeed. It

forms a low-pass filter with a -3 dB cut-off frequency FCH. Assuming that FCH is the highest frequency to be

amplified (with a 3 dB attenuation), the maximum value of Cfeed is:

FCH= 1

2π⋅Rfeed⋅Cfeed

(14)

Figure 77. Higher cut-off frequency vs. feedback capacitor

0.01

0.1

1

10

100

100

1k

10k

100k

Rfeed=40kΩ

Rfeed=80k Ω

Rfeed=20k Ω

Cfeed (μF)

Rfeed=10kΩ

5.5

Gain settings

In the flat frequency response region (with no effect from Cin, Cout, Cfeed), the output voltage is:

VOUT=VIN⋅ −RfeedRin =VIN⋅AV

(15)

The gain AV is:

AV=−RfeedRin

(16)

5.6

Decoupling of the circuit

Two capacitors are needed to properly bypass the TS488, a power supply capacitor Cs and a bias voltage bypass

capacitor Cb.

Cs has a strong influence on the THD+N in the high frequency range (above 7 kHz) and indirectly on the power

supply disturbances. With 1 µF, you can expect THD+N performance to be similar to the one shown in the

datasheet. If Cs is lower than 1 µF, the THD+N increases in the higher frequencies and disturbances on the power

supply rail are less filtered. On the contrary, if Cs is higher than 1 µF, the disturbances on the power supply rail are

more filtered.

TS488

Higher cut-off frequency

DS4579 - Rev 8

page 22/32