TDA7316 Datasheet, PDF (4/10 Pages) STMicroelectronics – FOUR BANDSDIGITAL CONTROLLED GRAPHIC EQUALIZER

TDA7316
DEVICE DESCRIPTION
The TDA7316 is a four 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 four
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:
fo = center frequency
Gv = gain/loss at the center frequency f_o
Gv = 20log(Av)
Q
=
f₂
f_o
−
f₁
where f₂, f₁ = 3dB Bandwidth limits.
Av
=
(R2
⋅
C2 )
(R2
+ (R2
⋅ C1 )
⋅ C1 )
+ (R2
+ (R1
⋅ C2 )
⋅
C1
)
Q
=
√(R1⋅C1⋅R2⋅ C2)
(R2 ⋅C1 ) + (R2 ⋅ C2 )
fo
=
2π
⋅
1
√(R1⋅R2⋅C1⋅ C2)
If C1 is fixed, then:
C2
=
A_v
Q²
−1−
Q²
⋅
C1
R2
=
2
π
⋅
C1
⋅
f_o
1
⋅ ^{(Av −1}
(A_v − 1
)⋅Q
− Q²)
R1
=
(A_v
A_v −
−
1
1)²
− Q²
⋅
R2
Likewise, the components values can be deter-
mined byfixing one of the other three parameters.
Referring to fig. 1 the suggested R2 value should
be higher than 2KΩ in order to have a good THD
(internal op. amp. current limit).
Viceversa the R1 value should be equal or lower
than 51KΩ in order to keep the ”click”(DC step)
very low.
A typical application is shown by fig. 2
Fig. 1
x = band number
y = left or right
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