9/16

STA550

Gain without compression (G)

= 5

Max Attenuation ratio

= 26 dB

The following graph gives the representation of the Compressor activation status related to the Vthreshold and

the input voltage. The delimitation line between the two fields, compression or not, is expressed by the formula :

Where G is the preamplifier gain without compression.

In the compression region the gain of the preamplifier will be reduced

(G = 2·Vthreshold/Vin) to maintain at steady state the output voltage equal 2*|Vthreshold| .

Instead in the other region the compressor will be off (G = 5).

The delimitation line between the two fields can be related to the output voltage of the preamplifier: in this case

the formula is :

Figure 2. Compressor activation field

The relative attenuation introduced by the variable gain cell is the following :

The total gain of the stage will be:

Gdb = 20log5 + Attenuation

The maximum input swing is related to the value of input resistor, to guarantee that the input current remain

under Iin_Max value (1 mA).

V

in

2Vthresh ol d

⋅

G

-------------------------------------------

=

V

out

2Vthre sho ld

⋅

=

1

2

4

6

8

2345

G = 5

|Vthreshold|

COMPRESSION

G < 5

D01AU1264

Attenu atio n

20

2

5

---

log

V

th

V

in _peak

----------------------

⋅

=

R

i

V

in_peak

I

in_max

----------------------

>