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Si4831/35 AM/FM/SW TUNER

FREQUENTLY ASKED QUESTIONS

Si4831/35 FAQ

SI4831/35 AM/FM/SW TUNER—FREQUENTLY ASKED QUESTIONS

Table of Contents

What's the advantage of using PVR tuning instead of PVC? . . . . . . . . . . . . . . . . . . . . . . . . . . 4

PVR tuning stable under different environmental conditions? . . . . . . . . . . . . . . . . . . . . . . . . . 5

What do I need to change on the appearance of my existing model if using Si4831/35? . . . . 6

How is the tuning feel of PVR with Si4831/35, is it easy to tune exactly to a station? . . . . . . . 6

How is the frequency display accuracy of Si4831/35 PVR tuning

compared with PVC tuning? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Why are some of my Si4831/35 models occasionally unable to power up

after quick power off/on cycles? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Why is the measured SNR and Sensitivity often better when using an audio analyzer

than when using a multimeter? 9

If my application is mono audio, how should I use Si4831/35? . . . . . . . . . . . . . . . . . . . . . . . . 9

When switching on the power supply, there is a small but audible power on pop noise.

How can this pop noise be mitigated? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Why is the narrow FM AFC range not a problem in the Si4831/35? . . . . . . . . . . . . . . . . . . . 10

How do I minimize the frequency display position hysteresis with PVR tuning? . . . . . . . . . . 10

Si4831/35 FAQ

4 Rev. 0.1

Q: What's the advantage of using PVR tuning instead of PVC?

Keyword(s): PVR, PVC, resistance ratio

Device(s): Si4831/35

HW Rev(s): All

A: PVR tuning has the following advantages compared with PVC tuning:

1. Cost saving

Material cost: PVR is $0.05 vs. PVC for $0.12 for the same quantity and quali ty

Labor cost

2. Reliable life time and endurance (test proven) is better than PVC

Test Method: 100,000 PVR full ra nge rotations

SINAD, SNR, sensitivity at three freq uency points remain unchanged before and after rotation test

PVR value and the frequency display mark stay within spec:

After 10K times rotations, PVR value stays the same, frequency/di s play alignment unchanged

After 100K times rotations, PVR value changes less than10%, no visible chan ge to frequency/display

alignment. This is because Si4831/35 uses resistance ratio, not the absolute resistance value, for tuning

to ensure display accuracy

Figure 1. PVR Resistance Ratio

FM Test

Points(MHz)

Before Test After Test

SINAD

(dB) S/N (dB) Sensitivity

(dBµV) SINAD

(dB) S/N (dB) Sensitivity

(dBµV)

88.1 57 58 2 57 58 2

98.1 57 58 2 57 58 2

107.9 56 57 3 56 57 3

Si4831/35 FAQ

Rev. 0.1 5

Q: PVR tuning stable under different environmental conditions?

Keyword(s): PVR tuning, environmental conditions

Device(s): Si4831/35

HW Rev(s): All

A. Yes, PVR tuning frequency stays stable at various conditions while PVC tuning frequency drifts. Reliability

test results proved the following:

Testing platform: Si4835-DEMO with R121 PVR and Sony clock radio ICF-C218 with PVC

Tuned frequency is determined at maximum SINAD and S/N point

Tests Settings Si4831/35 PVR SONY–ICF-C218 PVC

Hot temp / Humidity

Room(start) 98.1 MHz 98.1 MHz

T:45 °C,H:80% 98.1 MHz 98.14 MHz

Room(end) 98.1 MHz 98.1 MHz

Cold

Room(start) 98.1 MHz 98.1 MHz

T:–10°C 98.1MHz 98.17MHz

Room(end) 98.1 MHz 98.17 MHz

Long term high temp / humidity

(T = 60° C/H = 90%/10 0 Ho ur )

Room(start) 98.1 MHz 98.1 MHz

Room(end) 98.1 MHz 98.28 MHz

Short term high temp /humidity

(T = 60° C/H = 80%/6 Hour)

Room(start) 98.1 MHz 98.1 MHz

Room(end) 98.1 MHz 97.98 MHz

Short term cold

(T = –25° C/6 Hour)

Room(start) 98.1 MHz 98.1 MHz

Room(end) 98.1 MHz 98.1 MHz

Hot /cold cycle test

(T = 70° C/T = –10° C/5 cycles)

Room(start) 98.1 MHz 98.1 MHz

Room(end) 98.1 MHz 98.06 MHz

Si4831/35 FAQ

6 Rev. 0.1

Q: What do I need to change on the appearance of my existing model if using Si4831/35?

Keyword(s): Existing model

Device(s): Si4831/35

HW Rev(s): All

A. The traditional PVC frequency display is non-linear; however, the Si4831/35's advanced tuning algorithm

makes the tuned frequency linear with the PVR turning angle, so Si4831/35 offers more accuracy to estimate

the frequency from the analog display marking. To use Si4831/35 for existing PVC models, you only need to

change the frequency marking and make it linear.

Figure 2. PVC PVR Frequency Display

Q: How is the tuning feel of PVR with Si4831/35, is it easy to tune exactly to a station?

Keyword(s): Tuning feel

Device(s): Si4831/35

HW Rev(s): All

A: Compared with Si4830/34-A20, the Si4831/35 uses a new tuning algorithm that allows the user to hear one

station across a larger frequency range . At the same time, the user can easi ly feel or tell if the tuned position is

the best by the sound. The new tuning algorithm was added to improve the tuning feel and has been well

received in the mark etplace . The algo rithm was care fully op tim ize d such that sele ctivity was not compromised;

therefore, weak station is still easy to tune.

Q: How is the frequency display accuracy of Si4831/35 PVR tuning compared with PVC tuning?

Keyword(s): Frequency display accuracy

Device(s): Si4831/35

HW Rev(s): All

A: Si4831/35 PVR tuning frequency display accuracy is not any worse than traditional analog radios. The

tuning position inaccuracy has most to do with the PVR itself, but this is not unique to PVR. PVC will also have

some position inaccuracy. Traditional PVC tuning analog radio has a much more severe tuned position drifting

problem than Si4831/35, and for a longer term. PVR tuning position accuracy of the Si4831/35 is better; refer

to the second question for more information.

Si4831/35 FAQ

Rev. 0.1 7

Q: Why are some of my Si4831/35 models occasionally unable to power up after quick power off/on

cycles?

Keyword(s): Power off/on cycles, power up, reset, reset pulse

Device(s): Si4831/35

HW Rev(s): All

A: Sometimes, when the power switch is turned off/on quickly, or the power plug is plugged in/out quickly, the

Si4831/35 can't be powered up properly and it can't go into normal working mode. The reason for this is that,

during this type of fast power off/on process, the chip occasionally is not reset properly.

Si4831/35 is digital in nature—an MCU and a DSP are integrated inside the chip. To power up properly, the

chip needs a proper negative reset pulse during the quick power off/on cycle. As shown in Figure 3, the

needed pulse width of tSRST is several ms. Because there are large filtering capacitors in the power supply

circuit, the dc supply voltage VCC to tuner is still present (even though the main plug is disconnected) and falls

down slowly. Accordingly, the RST pin voltage falls down slowly, so there is no needed reset pulse generated.

Figure 5 shows a typical VCC and RST volt age chan ge curve during a power of f /on cycle. In this case, the RST

voltage level doesn 't drop below 0.3 VCC, so the chip is not reset properly and can't be powered up and go into

normal working mode.

Figure 3. Reset Pulse for Si4831/35

Figure 4. RC Reset Circuit of Si4831/35

70%

30%

tSRST

RST

GND

C19

0.1µ

VCC

RST

100k

Si4831/35 FAQ

8 Rev. 0.1

Figure 5. VCC (green) and RST (yellow) Change During Power Off

Figure 6. Typical Power Supply Circuit

Figure 6 shows the typical power supply circuit of a tuner; the solution to the power up issue is:

1. Add a discharge resistor at the output of tuner power supply to speed up the discharge process when the power is

off.

2. Optimize the filtering caps capacity to a small value. Si4831/35 consumes only around 20 mA current in normal

working mode, so the power supply circuits do not need to contain a large value of filtering caps; normally, no

more than 47 µF is recommended.

Si4831/35 FAQ

Rev. 0.1 9

Q: Why is the measured SNR and Sensitivity often better when using an audio analyzer than when using

a multimeter?

Keyword(s): Audio analyzer, multimeter, SNR, Sensitivity

Device(s): Si4831/35

HW Rev(s): All

A: Normally, there are two kinds of instruments used for measuring SNR and Sensitivity: one is a professional

audio analyzer and another is a multime ter or voltmeter, which can be a trad iti ona l ne edle d isplay type or mor e

modern digital display type. The voltmeter is low cost and is widely used by many audio customers. A typical

voltmeter model is TVT-322.

Using the audio analyzer, the measured SNR and sensitivity is normally better than when using a voltmeter for

the following reasons:

1. The frequency bandwidth of an audio analyzer is narrower than a voltmeter’s bandwidth. Audio analyzer

bandwidth is normally up to 22 kHz; this is the real audio signal band width. For the voltmeter, the frequency

bandwidth is much wider, and different models have different bandwidths, normally above 200 kHz. For the TVT-

322, the bandwidth is up to 1 MHz. Because of the wider frequency bandwidth, the voltmeter always measures a

higher noise level than the audio analyzer and therefore has a lower SNR value and Sensitivity value. But for true

audio measurement, the noise level above 22 kHz should not be counted as it is beyond the human ear frequency

audible range.

2. The audio analyzer is a more advanced instrument than the voltmeter; it can measure signal level and noise level

at the same time, and can directly calculate SNR data. For the voltmeter, SNR data can only be obtained by first

turning on modulation to get the signal level, then turning off modulation to get the noise level, and then calculating

SNR data as the delta. So for the voltmeter, the measured signal le vel and noise level do not occur at the same

time, hence it is not a true SNR me asurement.

Q: If my application is mono audio, how should I use Si4831/35?

Keyword(s): Mono Audio, Stereo Audio

Device(s): Si4831/35

HW Rev(s): All

A: The Si4831/35 is a stereo audio tuner wi th two stereo thresholds: 20 dBµV and 28 dBµV. When the input RF

level is below the selected stereo threshold, the chip outputs mono audio. When the input RF signal is above

the selected stereo threshold, it automatically outp ut s stereo audio . The following measures ar e recommended

for mono audio applications:

1. Choose the wanted FM band with stereo indication threshold of 28 dBµV.

2. Connect Lout and Rout together right after the AC coupling capacitors of 4.7 µF.

Q: When switching on the power supply, there is a small but audible power on pop noise. How can this

pop noise be mitigated?

Keyword(s): Pop noise

Device(s): Si4831/35

HW Rev(s): All

A. Compared with Si4830/34-A20, the Si4831/35 has greatly reduced the power on pop noise. To further

migrate the pop noise, the following measures are reco mmended:

1. The ac coupling capacitors in series with Lout and Rout of Si4831/35 must be no less than 4.7uF.

2. Normally, there is a large power supply filtering capacitor at th e power supp ly of audio AMP, put the capacitor as

close to the power supply pin of audio AMP as possible, and give this capacitor a large value, so that at power up,

audio AMP starts up more slowly than Si4831/35, this will make the power on pop noise smaller.

3. To completely remove the power on pop noise, adding a transistor + E-cap mu ting circuit as shown in Figure 7 to

Lout and Rout of Si4831/35 respectively.

Si4831/35 FAQ

10 Rev. 0.1

Figure 7. Power On Pop Noise Muting Circuit

Q: Why is the narrow FM AFC range not a problem in the Si4831/35?

Keyword(s): AFC Range, Traditional Analog FM tuner, Selectivity

Device(s): Si4831/35

HW Rev(s): All

A. For traditional analog FM tuners, the FM AFC range by standard measurement procedures is normally

between 150 and 500 kHz, but for Si4831/35, the tested AFC range is at 40–60 kHz based on the traditional

test method. The Si4831/35 has a digital architecture with an advanced tuning algorithm; therefore, it has

dynamic AFC range. When PVR is rotated during tuning, Si4831/35 broadens its AFC range to around

+/-500 kHz for easy station capturing a nd locking. When tuni ng is stoppe d, Si4831/35 auto matically narrows it s

AFC range to 40–60 kHz for excellent selectivity performance.

Q: How do I minimize the frequency display position hysteresis with PVR tuning?

Keyword(s): Position Hysteresis, Frequency Display, PVR tuning

Device(s): Si4831/35

HW Rev(s): All

A. The position hysteresis of the frequency display is caused by PVR itself and/or the mechanical structure of

the frequency display method. Si4831/35 itself has no frequency display hysteresis issue. PVRs are normally

used for volume control, where hysteresis is not an issue. Test results showed some PVRs have hysteresis

angles up to 4-5 degrees. Ask your PVR vendor to minimize the PVR position hysteresis. Most of the existing

mechanical structures for traditional analog radio frequency display method also fix the issue.

Si4831/35 FAQ

Rev. 0.1 11

NOTES:

Si4831/35 FAQ

12 Rev. 0.1

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