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Tuner Front End

M

Myauk

I have been studying the Tuner Front End Designs.
According to suggestions from previous discussions, I studied the
application notes and circuit diagrams of front end modules.
The following things are those that I am getting confused with:
1. According to my understanding, there are several allocated channels
for television according to CCIR, France, USA, or China Tables. Let's
say a tuner front end is connected to the antenna, the first thing it
needed to be done is to select a typical channel among the channels
available. I understand that 'tank circuit' is used with variable
capacitance to tune to the desired channel.

So I imagine that a tuning unit with varicap diode will do the
selection of channel. The capacitance is set by the voltage applied
(up to 33V range). And this voltage might be supplied by a typical DAC
and register where the values are set by I2C control.

But practically, when I studied the tuner application note, I found no
clue for setting the capacitance for tuner tank circuit.
What I found is something 'Charge Pump', Prescaler, Divider, 15 Bit
Counter, Phase Detector, Op-amp unit, detecting Local Oscillators,
(sorry if I presume wrongly) and the output VTU controls the tuning
part. (according to a tuner front end design using the IC: SN761678B
TV TUNER IC.
There I am confused!

Can anybody show me some links or explain to me about it so that I
could start learning?

Regards
 
F

Frank Raffaeli

I have been studying the Tuner Front End Designs.
According to suggestions from previous discussions, I studied the
application notes and circuit diagrams of front end modules.
The following things are those that I am getting confused with:
1. According to my understanding, there are several allocated channels
for television according to CCIR, France, USA, or China Tables. Let's
say a tuner front end is connected to the antenna, the first thing it
needed to be done is to select a typical channel among the channels
available. I understand that 'tank circuit' is used with variable
capacitance to tune to the desired channel.

So I imagine that a tuning unit with varicap diode will do the
selection of channel. The capacitance is set by the voltage applied
(up to 33V range). And this voltage might be supplied by a typical DAC
and register where the values are set by I2C control.

But practically, when I studied the tuner application note, I found no
clue for setting the capacitance for tuner tank circuit.
What I found is something 'Charge Pump', Prescaler, Divider, 15 Bit
Counter, Phase Detector, Op-amp unit, detecting Local Oscillators,
(sorry if I presume wrongly) and the output VTU controls the tuning
part. (according to a tuner front end design using the IC: SN761678B
TV TUNER IC.
There I am confused!

Can anybody show me some links or explain to me about it so that I
could start learning?

Regards

http://www.eetchina.com/ARTICLES/2006JUN/PDF/DTCOL_2006JUN26_RFR_TA_01.PDF

Frank Raffaeli
 
P

Phil Allison

"Myauk"
But practically, when I studied the tuner application note, I found no
clue for setting the capacitance for tuner tank circuit.



** TV and FM tuner modules typically have just one voltage control input
for adjusting the operating frequency.

That input connects to several internal varicaps, controlling tuned circuits
in the RF & local oscillator stages.

The design of the module ensures the RF and local oscillator tuned circuits
track as required.



........ Phil
 
J

Jan Panteltje

I have been studying the Tuner Front End Designs.
According to suggestions from previous discussions, I studied the
application notes and circuit diagrams of front end modules.
The following things are those that I am getting confused with:
1. According to my understanding, there are several allocated channels
for television according to CCIR, France, USA, or China Tables. Let's
say a tuner front end is connected to the antenna, the first thing it
needed to be done is to select a typical channel among the channels
available. I understand that 'tank circuit' is used with variable
capacitance to tune to the desired channel.

So I imagine that a tuning unit with varicap diode will do the
selection of channel. The capacitance is set by the voltage applied
(up to 33V range). And this voltage might be supplied by a typical DAC
and register where the values are set by I2C control.

But practically, when I studied the tuner application note, I found no
clue for setting the capacitance for tuner tank circuit.
What I found is something 'Charge Pump', Prescaler, Divider, 15 Bit
Counter, Phase Detector, Op-amp unit, detecting Local Oscillators,
(sorry if I presume wrongly) and the output VTU controls the tuning
part. (according to a tuner front end design using the IC: SN761678B
TV TUNER IC.
There I am confused!

Can anybody show me some links or explain to me about it so that I
could start learning?

Regards

Sometimes there is no 33V and a charce pump ciruit could be used
to make 33 from say 5V.
The osc frequency is deviced by the pre-scaler and compared to some reference..
The divider is often programmable so you can set the division rate for example via
i2c I do not know this chip you mention).
The opamp would amplify the 0-5V of a DA converter to 0-33V.
 
M

Myauk

http://www.eetchina.com/ARTICLES/2006JUN/PDF/DTCOL_2006JUN26_RFR_TA_0...

Frank Raffaeli- Hide quoted text -

- Show quoted text -

I have read the article.

According to the article, I learned about single conversion and double
conversion scheme.
But there is something I was not sure about.
While Selecting the desired channel among the frequencies in the
available range, let's say, 45 to 860 MHz, wouldn't it need tuning
circuit? (something like tank circuit?)
Or it is like the whole frequency range 45 to 860 MHz is downconverted
by mixing with Local Oscillator frequency, converting it into the
range in which the desired channel is sticking around the preferred IF
frequency (PLL?) and the rest are filtered out by using Band Pass
Filter? (referring to the block diagram of MC44S803)

And what is the High side/low side injection?
Now I am tracing the circuit design of the tuner to understand more
about it so that I could make my question more clearer for specific
answers.

Sorry for my ignorance in RF field. But I am quite eager to dig into
more details about it gradually until I understand the whole scheme of
tuning algorithm.(especially the popular hardware/software interface
scheme for tuning control)

Regards.
 
F

Frank Raffaeli

I have read the article.

According to the article, I learned about single conversion and double
conversion scheme.
But there is something I was not sure about.
While Selecting the desired channel among the frequencies in the
available range, let's say, 45 to 860 MHz, wouldn't it need tuning
circuit? (something like tank circuit?)
Or it is like the whole frequency range 45 to 860 MHz is downconverted
by mixing with Local Oscillator frequency, converting it into the
range in which the desired channel is sticking around the preferred IF
frequency (PLL?) and the rest are filtered out by using Band Pass
Filter? (referring to the block diagram of MC44S803)

And what is the High side/low side injection?
Now I am tracing the circuit design of the tuner to understand more
about it so that I could make my question more clearer for specific
answers.

Sorry for my ignorance in RF field. But I am quite eager to dig into
more details about it gradually until I understand the whole scheme of
tuning algorithm.(especially the popular hardware/software interface
scheme for tuning control)

Regards.

High side injection, which is more common in single-conversion down-
converters for TV, means that the local oscillator frequency = RF +
IF. This is now also the favored design practice in digital and hybrid
TV designs, using IF's of 44 or 36 MHz.

The amount of tuning in the front-end (before the mixer) varies by
design. In low-cost systems that use all-digital front-ends (e.g.
xceive), there is a band pre-selector. In tracking tuners like LG/
Innotek there is a varactor-tuned circuit before the mixer.

Frank
 
V

vasile

Sometimes there is no 33V and a charce pump ciruit could be used
to make 33 from say 5V.

The noise at the charge pump output is essential.
A few years back designing a DBVT board I've learned that.
MAX5025 is a good choice:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3138

The osc frequency is deviced by the pre-scaler and compared to some reference..
The divider is often programmable so you can set the division rate for example via
i2c I do not know this chip you mention).
The opamp would amplify the 0-5V of a DA converter to 0-33V.

No you don't need that. Modern circuits have constant 33V on varicaps
through a resistor.
Driving low the current through an open collector will allow 0 to 33v
reglage.

- Hide quoted text -
 
J

Jan Panteltje

The noise at the charge pump output is essential.
A few years back designing a DBVT board I've learned that.
MAX5025 is a good choice:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3138



No you don't need that. Modern circuits have constant 33V on varicaps
through a resistor.
Driving low the current through an open collector will allow 0 to 33v
reglage.

That will work, but in case 'opamp' with associated components you can have
more exact gain I think.
Anyways DA converter is a wide description here, a XOR phase comparator with
lowpass is also in a way an DA converter, but I think that was obvious.
Then perhaps there is a loop filter to be implemented, where the opamp high open
loop gain may help.

I must say that I have looked at some of these chips, and a lot has been integrated
making the tuner construction much simpler, say cheaper.
I had problems to identify the things that were left...once I designed my own
tuner.
How far will integration go? hard to integrate 60 Mhz (ch 3,4 etc VHF), but
UHF all in one chip? possible? (I mean no more inductors)?
 
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