UTC571

LINEAR INTEGRATED CIRCUIT

YOUW ANG ELECTRONICS CO.LTD

12

0

-100

-80

-60

-40

-20

0

VCA GAIN (0dB)

NOISE IN

20kHz BW

-40

-20

+20

110dB

90dB

MAXIMUM

SIGNAL LEVEL

Figure 12. Dynamic Range of UTC571

Figure 12 shows the noise performance of the DG cell. The maximum output level before clipping occurs in the

gain cell is plotted along with the output noise in a 20kHz bandwidth. Note that the noise drops as the gain is

reduced for the first 20dB of gain reduction. At high gains, the signal to noise ratio is 90dB, and the total dynamic

range from maximum signal to minimum noise is 110dB.

Control signal feedthrough is generated in the gain cell by imperfect device matching and mismatches in the

current sources, I 1 and I 2 . When no input signal is present, changing I G will cause a small output signal. The

distortion trim is effective in nulling out any control signal feedthrough, but in general, the null for minimum

feedthrough will be different than the null in distortion. The control signal

feedthrough can be trimmed

independently of distortion by tying a current source to the DG input pin. This effectively trims I . Figure 17 shows

such a trim network.

3.6V

R-SELECT FOR

TO PIN 3 OR 14

470k

100k

Vcc

Figure 13. control Signal Feedthrough