LC074146LP

No.A0906-25/31

• Video driver

Either 6dB or 12dB can be selected as the total gain of the video amplifier using the internal register setting

(VD_GAIN). When the input sync level is within the -12.5mV to 162.5mV range, the output sync level can be adjusted

to 0.1V using the internal register settings (VD_CTL1 [2:0] and VD_CTL2 [1:0]).

Description of ALC/Limiter (automatic level control) operation

Note: [xxxx] denotes a register name, and whatever is contained inside the parentheses “

” is applicable in the

PB-ALC mode.

The amplifier gain “digital volume value” of the PGA (programmable gain amplifier) is automatically adjusted so that

the A/D converter output audio level “digital volume output” is set to the ALC value [ALC_VAL [2:0]]. The PGA

“digital volume” gain can be varied in the -14dB to +34dB range. The maximum value [ALC_VMAX [5:0]] can be

set in this variable range.

=> If [ALC_VMAX [5:0]] is set to the maximum value of +34dB, the ALC functions can be used to the maximum.

=> If [ALC_VMAX [5:0]] is set to +0dB, it will no longer be possible to increase the gain in the “+” direction so

the ALC function will work in the same way as a limiter.

• ALC settings

(a) Power-saving function

When [PGA_PDX] is 0, the ALC circuit and PGA circuit are set to power down mode.

(b) Manual function

When both [REC_ALC] and [PB_ALC] are 0, manual mode is established.

In the REC_ALC mode, the PGA gain is fixed at the manual mode value [ALC_GAIN [5:0]].

In the PB_ALC mode, the digital volume level is fixed at [EVR_GAIN [6:0]].

(c) System operation

ALC is performed by feeding back the A/D converter “digital volume” data. Accordingly, configure the settings as

shown in the table below in order for the ALC functions to be activated.

REC-ALC

PB-ALC

PGA_PDX

1

0

ALCOFF

0

0

ADC_PDX

1

x

DAC_PDX

x

1

REC_ALC

1

0

PB_ALC

0

1

VIN Sync DC

(-12.5mV to 162.5mV)

(12.5mV/step) is adjustable to

VOUT Sync DC (100mV)

75

Ω

0V

LPF

ATT

VIN

VOUT

REG

-6dB/0dB

0dB

VREF1

12dB

CTL

(VD_GAIN )

VREF2