SI4713-B30-GMR【PDF 22/42 页】IC TX FM RADIO RPS/RDS 20UQFN

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录57

18页 19页 20页 21页 [22页]23页 24页 25页 26页

Si4712/13-B30

Rev. 1.1

5.3.1. Stereo Encoder

Figure 14 shows an example modulation level

breakdown for the various components of a typical MPX

signal.

The total modulation level for the MPX signal shown in

Figure 14, assuming no correlation, is equal to the

arithmetic sum of each of the subchannel levels

resulting in 102.67 percent modulation or a peak

frequency deviation of 77.0025 kHz (an instantaneous

frequency deviation of 75 kHz corresponds to 100

percent modulation). Frequency deviation is related to

the amplitude of the MPX signal by a gain constant,

VCO

, as given by the following equation:

where 攆 is the frequency deviation; K

VCO

is the

voltage-to-frequency gain constant, and A

is the

amplitude of the MPX message signal. For a fixed

VCO

, the amplitude of all the subchannel signals within

the MPX message signal must be scaled to give the

appropriate total frequency deviation.

Figure 14. MPX Encoder

Figure 14 shows a conceptual block diagram of an MPX

encoder used to generate the MPX signal. L(t) and R(t)

denote the time domain waveforms from the left and

right audio channels, and RDS(t) denotes the time

domain waveform of the RDS/RBDS signal.

The MPX message signal can be expressed as follows:

m(t) = C

[L(t) + R(t)] + C

cos(2?/SPAN>19 kHz)

+ C

[L(t) R(t)] cos(2?/SPAN>38 kHz)

+ C

RDS(t) cos(2?/SPAN>57 kHz)

where C

, C

, and C

are gains used to scale the

amplitudes of the audio signals (L(t) ?R(t)), the 19 kHz

pilot tone, and the RDS subcarrier respectively, to

generate the appropriate modulation level. To achieve

the modulation levels of Figure 14 with

VCO

= 75 kHz/V, C

would be set to 0.45; C

would be

set to 0.1, and C

would be set to 0.0267 giving a peak

audio frequency deviation of 0.9 x 75 kHz = 67.5 kHz, a

peak

pilot

frequency

deviation

0.1 x 75 kHz = 7.5 kHz, and a peak RDS frequency

deviation of 0.0267 x 75 kHz = 2.0025 kHz for a total

peak frequency deviation of 77.0025 kHz.

In the Si4712/13, the peak audio, pilot, and RDS

frequency deviations can be programmed directly with

the Transmit Audio, Pilot, and RDS Deviation

commands with an accuracy of 10 Hz. For the example

in Figure 14, the Transmit Audio Deviation is

programmed with the value 6750, the Transmit Pilot

Deviation with 750, and the Transmit RDS Deviation

with 200, generating peak audio frequency deviations of

67.5 kHz, peak pilot deviations of 7.5 kHz, and peak

RDS deviations of 2.0 kHz for a total peak frequency

deviation of 77 kHz. The total peak transmit frequency

deviation of the Si4712/13 can range from 0 to 100 kHz

and is equal to the arithmetic sum of the Transmit

Audio, Pilot, and RDS deviations. Users must comply

with local regulations on radio frequency transmissions.

Each of the individual deviations (transmit audio, pilot,

and RDS) can be independently programmed; however,

the total peak frequency deviation cannot exceed

100 kHz.

The Si4712/13 provides an overmodulation indicator to

allow the user to dynamically set the maximum

deviation level. If the instantaneous frequency exceeds

the

deviation

level

specified

the

TX_AUDIO_DEVIATION property, the SQINT interrupt

bit (and optional interrupt) will be set.

攆

VCO

57 kHz

MPX Encoder

m(t)

RDS(t)

Frequency

Doubler

Frequency

Tripler

L(t)

R(t)

38 kHz

19 kHz

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式