ULA1145

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

9 of 10

www.unisonic.com.tw

QW-R106-006.a



SOFT MUTE CHARACTERISTICS

1. Control

The S/N setting (C/N) for weak inputs and the -3dB limiting sensitivity can be controlled by obtaining the proper

value for the un-soft muted input/output signal characteristic. However, usable sensitivity cannot be controlled as this

is determined by the front end and IF design which are unrelated to soft muting.

2. Soft mute setting

Soft mute operation depends on the S-meter circuit voltage and the hole detection circuit voltage. As shown in the

graph on the right, the degree of soft muting correlates with the mute drive voltage, V15. The control signal line of

the mute drive voltage switches before and after the 10dBμ ANT divergence point.

When adjusting the soft mute with a weak signal which does not affect the S-meter, first adjust it using the hole

detection input signal. However, as the S-meter output will readjust the soft mute level, also adjust the soft mute

using the S-meter output. At this point, the hole detection output adjusts the gain up to the IF input, causing a

variance. Also, the S-meter output is varied by the value of R16.

Hole detector

S-meter

(Adjust R4, R5)

ANT input level (dBµ)

3. Soft mute transition response characteristic

The degree of soft muting automatically varies according to the change in input field strength. Omitting the

influence of the front end wideband AGC circuit, the UTC ULA1145’s response speed is dependent on the time

constant at pins 16 and 17.