DEVICE DESCRIPTION

The TDA7317 is a five bands, digitally controlled

stereo Graphic Equalizer.

The device is intended for high quality audio ap-

plication in Hi-Fi, TV and car radio systems where

feature like low noise and THD are key factors. A

mixed Bipolar Cmos Technology allows:

Cmos analog switches for pop free commuta-

tions, high frequency op.amp. (GWB = 10MHz)

and high linearity polisilicon resistor for THD =

0.01 (at Vin = 1Vrms) and a S/N ratio of 102dB.

The internal Block Diagram is shown on page 1.

The first stage is a volume control. The control

range is 0 to -17.625dB with 0.375dBstep.

The very high resolution (0.375dB step) allows

the implementation of closed loop amplitude con-

trol system completely free from any acustical ef-

fect (stepping variation and pumping effect).

The volume control is followed by a serial five

bands equalizer. Each filtering cell is the biquad

cell shown in fig. 1

The internal resistor string is fixing the boost/cut

value while the buffer makes the Q (quality factor)

and central frequency, set by external compo-

nents, fully indipendent from the internal resistors.

Each filtering cell is realized using only 4 external

components (2 capacitors and 2 resistors) allow-

ing a flexible selection of centre frequency fo, Q

factor and gain. Here below the basic formulae

and the key features of each band pass filter are

reported:

Gv = 20log(Av)

Q

=

= (

R2

⋅ C2 )+(R2 ⋅ C1 )

(R2 ⋅ C1 )+ (R2 ⋅ C2 )

Q

= √

(R1

(R2 ⋅C1 )+ (R2 ⋅ C2 )

=

1

2

π ⋅√

If C1 is fixed, then:

C2

=

Q

2

R2

=

1

2

−1 ) ⋅ Q

R1

= (

− 1

⋅ R2

Likewise, the components’values can be deter-

mined by fixing one of the other three parameters.

Referring to fig. 1 the suggested R2 value should

be higher than 2K

Ω in order to have a good THD

(internal op. amp. current limit).

Viceversa the R1 value should be equal or lower

than 51K

Ω in order to keep the ”click”(DC step)

very low.

A typical application is shown by fig. 2

Fig. 1

TDA7317

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