ak4145 AKM Semiconductor, Inc., ak4145 Datasheet - Page 24

• Manufacturer Part Number: ak4145
• Description: Digital Stereo Btsc Encoder
• Manufacturer: AKM Semiconductor, Inc.

1. Grounding and Power Supply Decoupling
The AK4145 requires careful attention to power supply and grounding arrangements. AVDD, DVDD and TVDD are
usually supplied from analog supply in system. If AVDD1, AVDD2, DVDD1, DVDD2 and TVDD are supplied
separately, the power up sequence is not critical. VSS of the AK4145 must be connected to analog ground plane.
System analog ground and digital ground should be connected together near to where the supplies are brought onto the
printed circuit board. Decoupling capacitors should be as near to the AK4145 as possible, with the small value ceramic
capacitor being the nearest.
2. Voltage Reference Inputs
The voltage of AVDD sets the DAC analog output range. VCOM is signal ground of analog output signal. FILT pin is
Loop filter pin for internal PLL. An electrolytic capacitor 10μF parallel with a 0.1μF ceramic capacitor attached between
the VCOM pin and VSS pin eliminate the effects of high frequency noise. An 4.7nF capacitor should be attached between
the FILTM pin and VSS pin. No load current may be drawn from these VCOM pin, FILT pin. All signals, especially
clocks, should be kept away from the AVDD, VCOM and FILT pins in order to avoid unwanted coupling into the
AK4145.
3. Analog Video Input
In case of composite video input mode (VCLK bit = “0”), the AK4145 receives the analog video input through the
CV27M pin using a 0.1μF ceramic capacitor in series. This video signal is used for the synchronization between the video
sync and the pilot frequency on composite audio output. The video input mode is NOT available only when the TVDD is
lower than 2.7V. In case of 27MHz clock input mode (VCLK bit = “1”), input the 27MHz clock directly without using the
0.1uF capacitor.
4. Analog Composite Audio Output
The analog output is single-ended and centered on around the VCOM voltage. The output signal range scales with the
supply voltage and nominally 2.2 x AVDD/3.3 Vpp at CA pin. DC offsets on analog outputs are eliminated by AC
coupling. The modulation level of sound intermediate frequency (SIF) at RF modulator can be adjusted by the internal
volume control of AK4145 (04H D7-0 ATT7-0 bits). The stereo separation can be maximized by tuning the modulation
level. If the output level of AK4145 (typ: 2.2Vpp) is not sufficient for the RF modulator device, the external gain stage
can be used for the extra gain.
Rev. 0.3
AK4145
CA
Figure 17. External Gain Stage Example (if required).
10u
47k
47k
Vop
22k
0.1u 10u
- 24 -
Vop
10u
RF Modulator
[AK4145]
2007/11