peak-to-peak detector of fig. 16 is now inside the

broken line 1 while the system which allows a di-

namic resistance varying with the DC voltage

level (i.e. inversely proportional to the op-amp

output signal),is inside the broken line 2.

It should be noted that the generator resistance

Ri

has no influence on the controlled voltage

value Vc, although its value should be between 1

and 47 Kohm.

The lower limit is determined by the minimum dy-

namic resistance

of 10 ohm and therefore to

have a control range of 40 dB for the input signal,

Ri must be greather than 1.5 Kohm.

The upper limit results from the necessity to limit

the attenuation of the signal by the input imped-

ance of the op-amp.

Switches

Two DC-controlled switches are also included in

the chip (fig. 20 )

Fig. 19 shows the typical application circuit of the

TDA7284 utilizing the equalization switch for nor-

mal or chrome tape playback equalization.The

advantage is the components can be placed near

to the IC, while the tape selector switch can be at

a remote location, hence reduce the chances of

noise and oscillation due to components layout.

Another advantage is that only one pole is

needed for the tape selector switch as compared

to the two poles needed by conventional circuits

(one separate pole for each channel).

Fig. 22 shows the use of the switches to obtain

the mute function.

Figure 20

Figure 21: Application Circuit with DC Switching of Normal/Chrome Tape Equalization

TDA7284

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