ML6411 Просмотр технического описания (PDF) - Micro Linear Corporation

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ML6411

Programmable Video Digitizer with Selectable Gain and Clamps

Micro Linear Corporation 

FUNCTIONAL DESCRIPTION

GENERAL

The Universal Video Digitizer is a single-chip Video A/D

converter with an analog front end which is intended for

analog to digital conversion of 2V peak-to-peak (VP-P) or

1VP-P signals at rates up to 30 MSPS through a high

performance A/D with ±½ DNL performance. It forms a

complete solution for data conversion of dual CV and Y/C

signals including gain settings and clamp settings by

incorporating clamps, user selectable gain controls (UGC

and SGC), bias and clock generation.

The ML6411 consist of two video clamps, two sample and

hold amplifiers, two three-stage pipeline A/D converters,

digital error correction circuitry, selectable clamps,

programmable gain control, bias voltage generation and

clock generation. The operating power dissipation is

425mW typical.

INPUT FOR VARIOUS VIDEO MODES

The ML6411 can digitize various analog video inputs:

S-Video (Y/C), or composite video (CV). Again, for each

video channel, the gain and clamps can be selected.

A description of each of these modes is described

below. The Table 1 below provides a summary of the

various modes.

Dual Channel Composite Video (CV1 and CV2) Mode

The composite input channels are provided through the Y/

CV1 (A channel) and C/CV2 (B channel) pins. To activate

this mode, the CV/S_Mode Bit (Register D, Bit D3) must set

HIGH (D3=1). This mode is selectable via serial bus. In

this mode, the two S&H circuits for each channel can be

clocked up to 30MHz. Each CV channel can be then

scaled for a desired gain setting using the User Gain

Control (UGC). Standard gain selection can also be

chosen using the preset gain modes for 2VP-P signals only.

For 1VP-P signals, the preset gain selection mode is not

available; however the UGC functions can be used to

select gain values. The preset gain modes are for typical

NTSC or PAL composite video and are selectable via serial

bus through the STDA<1:0> and STDB<1:0> (Register B,

Bits B4, B3, B2, and B1) bits. When using the preset gain

mode, the output signals are enhanced by amplifying the

input signal by the value of GPRESET (see Table 2). In

addition, the clamp levels can be selected for either

channel for 16, 24, 64, and 128 binary levels (depending

on the channel) via the serial bus through the CLPA<1:0>

and CLPB<1:0> bits (see Table 3).

S-Video (Y / C) Mode

The input channels are provided through the Y/CV1 (A

channel) and C/CV2 (B channel) pins. To activate this

mode, the CV/S_Mode Bit (Register D, Bit D3) must be set

LOW (D3=0). This mode is selectable via serial bus. In this

mode, the two S&H circuits for each channel can be

clocked up to 30MHz. Each channel (Y and C) can be

then scaled for a desired gain setting using the User Gain

ML6411

Control (UGC). Standard gain selection can also be

chosen using the preset gain modes for 2VP-P signals only.

For 1VP-P signals, the preset gain selection mode is not

available; however the UGC functions can be used to

select gain values. The preset gain modes are for typical

NTSC or PAL S-Video and are selectable via serial bus

through the STDA<1:0> and STDB<1:0> (Register B, Bits

B4, B3, B2, and B1) bits. When using the preset gain

mode, the output signals are enhanced by amplifying the

input signal by the value of GPRESET (see Table 2). In

addition, the clamp levels can be selected for either

channel for 16, 24, 64, and 128 binary levels (depending

on the channel 24 not available for C-channel) via the

serial bus through the CLPA<1:0> and CLPB<1:0> bits (see

Table 3).

Input Voltage Selection

The ML6411 can support 1VP-P and 2VP-P input video.

Selection for the voltage input is programmed via control

register on the APEAK and BPEAK bits, A channel and B

channel, respectively (see Table 7).

GAIN SELECTION CONTROL (UGC AND SGC)

There are two separate control mechanisms that can be

used to scale gain settings for the incoming video format:

User Gain Control (UGC) and Sync-suppressed Gain

Control (SGC).

User Gain Control (UGC)

The user gain control function is achieved through a

variation of the full scale range of the A/D converters. This

will provide the user with approximately +/-3dB gain

variation as needed. Y reference and C reference are

supplied by two independent DACs. The user can adjust

the gain of each ADC independently providing the 6-Bit

code for the gain control through serial interface for each

A/D. Each step change can increment or decrement the

gain by 3% and allows for up to 64 different gain setting

levels per channel. The UGC can be used for both 1V and

2VP-P inputs. When using the UGC mode, the output

signals are enhanced by amplifying the input signal by the

value of GUGC. Table 4 provides a summary of the possible

incremental ranges. The gain accuracy of the UGC for

each of the 64 levels is +/-1.5%. The UGC gain settings

are selected via serial bus by programming Registers C, D,

and E on the GNA<5:0> bits for the A-channel and

GNB<5:0> bits for the B-channel.

Unity gain is set at default for GNA<5:0> = 100,000 and

GNB<5:0> = 100,000. For values of GNA<5:0> and

GNB<5:0> from 100,000 to 111,111, the gain increases

monotonically from 0dB (unity gain) to almost 3dB

(actually 1.48x), while from 100,000 to 000,000 the gain

decreases monotonically from 0dB (unity gain) to –3dB

(0.5x). Note that Table 4 provides only approximation of

gain values: actual gain values can vary from device to

device.

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