10.7 MHZ oscillator for SA636 IC - Need help

Good night.
I am using the SA636 IC (**broken link removed**) to modulate/demodulate an fsk signal in wich the central frequency is 10.7MHZ. I need to use a 10.7MHZ oscillator in the mixer. I don't know wich type of oscillator (colpitts or hartley). Can someone help me? The pins to the oscillator are 3 (oscillator out) and 4 (oscillator in), but i don't know the connections that i have to make.
In the application circuit in the datasheet they don't specify the oscillator, they just mention a frequency!

Thanks for any help.

Best regards.

Sorry for my English.

Castanheira

I can understand your confusion. That is truly one of the worst data sheets I have ever seen published!

If you have a 10.700 MHz FSK modulated signal, and want to receive it with that chip, you do not want to use the oscillator at all. Using the Fig 2 pinouts, You would hook up your antenna to PIN 18, where PIN 19 is coupled to ground with a capacitor. You would buy a 10.7 MHz ceramic bandpass filter, and place it between pins 14 & 16, with pins 17, 12 and 13 capacitive coupled to ground. You probably want to hook a resistor to ground on pin 2, to keep the "oscillator" from randomly oscillating. You need to put a resonant circuit at 10.7 MHz between pins 10 and 11 for the FSK demodulator to work properly, as shown in figure 15.

The chip, although you can't tell from the data sheet, is really a 150 MHz to 1000 MHz FSK receiver. To use it at 10.7 MHz, you have to bypass the downconversion stage at the input.

Thank you for your answer, again

Yes, for the demodulation I don't need to use the downconversion mixer because i already have an fsk signal modulated with a central frequency of 10.7 MHz.
But now, as i am using this chip for my application, my thesis professor said to use the mixer, not as a down conversion mixer, but as an upconversion mixer.
The band base frequencies are generated using the pwm of a microcontroller and i use the mixer to make the upconversion of the modulated signal.
Now i don't realy now the connections that i have to make in pins 3 and 4 to make a 11.2896MHZ oscillator for the mixer. With this frequency the "1" frequency will be about 10.8MHZ and "0" frequency will be 10.6 MHZ.
One more question, between the pins 11 and 10 i have to connect the ressonant circuit, but in the datasheet they use an if Frequency of 9.8 MHZ. What changes do i have to make in order to change that? In the varicap?

Sorry for bothering you and thank you for your time.

Best regards

Castanheira

That mixer is designed as an downcoverter. You have to feed the input to RFin, and take the output from Mixer out. It is not at all clear that you could use the mixer as an upconverter, as the input stanges may not work at a low frequency, and the mixer out pins may not work at a high frequency. You could get one and test it.

Or you could find a chip specifically design as an FSK transmitter for your intended frequency band.

biff44 said:

That mixer is designed as an downcoverter. You have to feed the input to RFin, and take the output from Mixer out. It is not at all clear that you could use the mixer as an upconverter, as the input stanges may not work at a low frequency, and the mixer out pins may not work at a high frequency. You could get one and test it.

Or you could find a chip specifically design as an FSK transmitter for your intended frequency band.

Click to expand...

I think that for the frequencies that i am using there are no chips to make the modulation. I have already ordered some sa636 to try the mixer, and check if i can use it as an upconverter. For the oscillator i still have some doubts. Can i use the same schematic of the oscillator in the sa606 scheme? **broken link removed** Fig.16.
What changes do i have to make in the oscillator for 11.2896MHZ?

Thanks for your reply.

Castanheira

what is your wireless frequency? And what is your data rate?

What do you mean by wireless frequency? My data rate is what i can get. First we will try to achieve 100kbps!
The type of communication that i am using is BAN (Body area network). I don't use an antenna, i use an electrode with 2/3 cm above the ground plane. This type of communication does not have such a high range like wireless. I don't know if i answered your question!

Thanks

Lets slow down for a second and iron out the basics.

I assume you are transmitting data wirelessly from one location to another. For that you need a transmitter at one position, a receiver at another position, and the data magically flows through the air between the two. Yes/No?

To send data with such a system, you have the transmitter set up to use a carrier frequency, and you modulate the data onto that carrier. The carrier frequency might, for example, be 100 MHz, and you modulate you 100 kbps data onto that carrier by making the frequency deviate +/- a little. For example a "1" would be 100.05 MHz, and a "0" might be 99.95 MHz. In this case I would say:
Wireless carrier frequency:100 MHz
Frequency Deviation: 50 KHz
Data Rate: 100 kbps

So for your case, what is the carrier frequency, deviation, and data rate you would like to use?

biff44 said:

Lets slow down for a second and iron out the basics.

I assume you are transmitting data wirelessly from one location to another. For that you need a transmitter at one position, a receiver at another position, and the data magically flows through the air between the two. Yes/No?

To send data with such a system, you have the transmitter set up to use a carrier frequency, and you modulate the data onto that carrier. The carrier frequency might, for example, be 100 MHz, and you modulate you 100 kbps data onto that carrier by making the frequency deviate +/- a little. For example a "1" would be 100.05 MHz, and a "0" might be 99.95 MHz. In this case I would say:
Wireless carrier frequency:100 MHz
Frequency Deviation: 50 KHz
Data Rate: 100 kbps

So for your case, what is the carrier frequency, deviation, and data rate you would like to use?

Click to expand...

Yes, I am transmitting data wirelessly from one location in the human body (my wrist for example) to another part of my body. This project is to use body sensors network that every sensor/transceiver can comunicate with the others!
Now i am doing this just for two transceivers one transmitting and one receiving.
The carrier i am using is 10.7Mhz wich is the frequency that the chanel (human body) "presents" best response (noise, attenuation...).
My frequency deviation is 100khz - "1" - 10.8MHZ and "0"-10.6MHZ.
For the modulation i wanted to use two oscillators with these two frequencies, but in order to spare space in the PCB the modulation is going to be made with the microcontroller (f1=689.6Khz and f0=489.6Khz) and than upconverted using the mixer with fosc=11.2896MHz.
The data rate is about 100khz.

Sorry for the English. If you don't understand something just say.

It might just work the way you think. The frequencies are low enough. You want to put your 600 KHz IF into the RF IN. And you want to take your RF output from the IF Out pin.

For initial testing you can just jam an 11 mhz signal into the oscillator pin. After it seems to be working fine as a transmitter, you can try putting a crystal resonator at the oscillator pin, and playing around with some shunt capacitors you might be able to get it to self oscillate for you.

biff44 said:

It might just work the way you think. The frequencies are low enough. You want to put your 600 KHz IF into the RF IN. And you want to take your RF output from the IF Out pin.

For initial testing you can just jam an 11 mhz signal into the oscillator pin. After it seems to be working fine as a transmitter, you can try putting a crystal resonator at the oscillator pin, and playing around with some shunt capacitors you might be able to get it to self oscillate for you.

Click to expand...

Next week I will try the sa636 circuit as receiver and as transmitter and then I see if i can get the results that i am expecting.

Thank tou very much for your help.

Best regards.

Castanheira

Colpitt oscillator.

Use 10.7 MHz xtal spec'd at given load capacitance. Feedback caps are placed between B-C (larger value) pin 3&4, and from emitter, pin 3, to ground.

Assume crystal load spec capacitance is 20 pF, assume Cbe is 5 pF and Ce to ground is 2 pF. Cbe(pin 3 to 4) should be about 82 pF, C from emitter(pin3) to ground is about 27 pF. Crystal is connected at base (pin 4) to ground. Series combination of 82 pF + 5 pF and 27 pF + 2 pF should be close to 20 pF crystal load capacitance requirement. 87 pf in series with 29 pF = 21.75 pF. Feedback ratio of caps should be about 3 or 4 to 1.

Vcc (pin 5) needs a bypass cap to ground. 0.01 uF would do.