ISD8101
ISD8101 Datasheet Rev. 1.8 - 15 - Nov, 2012
7.3
D
IFFERENTIAL
I
NPUT FOR
A
NALOG OR
PWM
The following application example is for reference, and is only to give a general idea how to use the
ISD8101. Each end-product design must be optimized in its own system for the best performance on
voice quality, power consumption, functionality, and all other issues.
Figure 8-2 ISD8101 Application Diagram
DESIGN SUGGESTIONS
1.) Choose the desired Gain or amplification factor: G = R3/(R1+Rg) and then calculate the value for
Rg = R3/G - R1 and use R1=5.5k-ohm and R3=55k-ohm. Both Rg parts should be the same value.
2.) Choose the desired low-pass frequency: Fc = 1/(6.28*Req*Ceq) where Ceq = 2*Cf and Req = R1
|| Rg to calculate the value of Cf. For a PWM circuit, Fc should be about one-half the audio sample
rate.
3.) Choose the desired high pass-frequency: Fc = 1/(6.28*Rin*Cin) and then calculate the value for
Cin = 1/(6.28*Rin*Fc) and use Rin=Rg+R1 and Fc = high-pass frequency in Hz. Cin value is Farads.
It is best to choose Cin as small as possible and both Cin parts should be the same value. This will
minimize cost and any pop/click sound.
4.) Choose the value for Cref. Note that Cref does not generate any pop/click timing and that the
main use for Cref is to filter any supply voltage noise. So, if the power supply noise is not a big
concern, then Cref can be small. Typical values for Cref can be between 0.1uF and 10uF, and a
recommended value for general applications is from 1uF to 4.7uF. In general, it is best if Cref is at
least 3x larger in value than Cin. This can help minimize the first-time power-on pop noise. After the
first-time power-on, the Cref value has no effect on pop/click performance.
5.) Choose the value for Cbulk. This value will depend on the both the physical layout (size and
length of PCB traces/wires) and the power supply properties. The suggested value for Cbulk is
100uF and is recommending to put close to the device . If the power supply is far away or weak,
then Cbulk may need to be a larger value. If the power supply is close and has high current capacity,
then it may be possible to use a smaller value for Cbulk. If Cbulk is too small, the system can be
unstable and may oscillate.
