HMP8170 datasheet(13/33 Pages) RENESAS

13 / 33 page

HMP8170

FN4284 Rev 6.00

Page 13 of 33

Sep 2003

Analog Outputs

The HMP8170 converts the video data into analog signals

using four 10-bit DACs running at the CLK2 rate. The DACs

output a current proportional to the digital data. The full scale

output current is determined by the reference voltage VREF

and an external resistor RSET. The full scale output current is

given by:

IFULLSCALE (mA) = 3.9 * VREF (V)/RSET (k)

(EQ 1.)

VREF must be chosen such that it is within the part’s operating

range; RSET must be chosen such that the maximum output

current is not exceeded.

If the VREF pin is not connected, the HMP8170 uses the

internal reference voltage. Otherwise, the applied voltage

overdrives the internal reference. If an external reference is

used, it must decoupled from any power supply noise. An

example external reference circuit is shown in the Applications

section.

The HMP8170 generates 1VP-P nominal video signals across

37.5

 loads, corresponding to doubly terminated 75 lines.

The encoder may also drive larger loads. The full scale output

current and load must be chosen such that the maximum

output voltage is not exceeded.

Output DAC Filtering

Since the DACs run at 2x the pixel sample rate, the sin(x)/x

rolloff of the outputs is greatly reduced, and there are fewer

high frequency artifacts in the output spectrum. This allows

using simple analog output filters. The analog output filter

should be flat to Fs/4 and have good rejection at 3Fs/4.

Example filters are shown in the Applications section.

Composite + Y/C Output Mode

The HMP8170 provides composite with S-video output mode.

When S-video outputs are selected, the encoder outputs the

luminance, modulated chrominance, and two copies of the

composite video signals. All four outputs are time aligned. The

output pin assignments are summarized in Table 12.

Composite + RGB Output Mode

When analog RGB video is selected, the HMP8170

transforms the filtered 8:8:8 YCbCr data into 8:8:8 RGB data.

The transform matrix uses different coefficients to generate

NTSC or PAL video levels.

The analog RGB outputs have a range of 0.3-1.0V with an

optional blanking pedestal. Composite sync information

(0.0-0.3V) may be optionally added to the green output. VBI

data is not included on the RGB outputs. The HMP8170 also

generates composite video when in RGB output mode. All four

outputs are time aligned.

The HMP8170 provides selectable pin outs for the RGB

outputs. When the SCART compatibility bit is cleared, the

analog composite video is output onto the NTSC/PAL 1 pin.

Red information is output onto the NTSC/PAL 2 pin, blue

information is output onto the C pin, and green information is

output onto the Y pin.

When the bit is set, the analog composite video is output onto

the Y pin. Red information is output onto the C pin, blue video

is output on the NTSC/PAL 2 pin, and the green signal is

output on the NTSC/PAL 1 pin. The output pin assignments are

summarized in Table 12.

Composite + YUV Output Mode

When analog YUV video is selected, the HMP8170 scales the

filtered YCbCr data to match the levels required by its DACs.

During the scaling, values less than 16 are clamped to 16.

The scaling factors for Cb and Cr are the same, but the CbCr

scaling factor is different from the Y scaling factor. The

encoder uses different sets of scale factors for NTSC and

PAL to accommodate their different black levels.

The analog YUV outputs have a range of 0.3-1.0V with an

optional blanking pedestal. Composite sync information

(0.0-0.3V) may be optionally added to the Y output. VBI data is

included on the Y output. The HMP8170 also generates

composite video when in YUV output mode. All four outputs

are time aligned. The output pin assignments are summarized

in Table 12.

Power Down Modes

To reduce power dissipation, any of the four output DACs may

be turned off. Each DAC has an independent enable bit. Each

output may be disabled in the host control register.

TABLE 12. OUTPUT PIN ASSIGNMENTS

PIN NAME

PIN #

OUTPUT MODE (SCART SELECT BIT)

COMP. WITH Y/C

(X)

COMP. W/ RGB

(0)

COMP. W/ RGB

(1)

COMP. W/ YUV

(X)

Luma

Green

Composite

Chroma

Blue

Red

NTSC/PAL 1

Composite

Green

NTSC/PAL 2

Composite

Red

Blue

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