Fully integrated ALL- CMOS AM transmitter with automatic antenna tuning

Abstract

A monolithic AM transmitter is disclosed. An external antenna forms part of a resonance network so that the antenna resonance point is automatically tuned to the transmit frequency. This provides flexibility with no added cost to the transmitter.

1. A transmitter comprising:
 an oscillator forming part of a phase-lock loop (PLL), the oscillator in combination with the phase-lock loop generating a transmit frequency of the transmitter in response to a frequency reference, the oscillator including a resonant network;  
 a modulator, a portion of said oscillator and said modulator being formed on a single monolithic chip, wherein part of the resonant network is formed on the monolithic chip, the resonant network of the oscillator being completed by an antenna formed external to the single monolithic chip, a resonance frequency of said resonant network being automatically tuned by the phase-lock loop to the transmit frequency, and wherein the oscillator includes a differential structure of varactor diodes for tuning a resonance point of the antenna to the frequency of the oscillator; and  
 a varactor charge pump formed on the single monolithic chip to provide a bias charge for varactor diodes in the differential structure of varactor diodes.  
 
     
     
       2. The transmitter of  claim 1 , wherein the phase-lock-loop further includes a phase detector, the phase detector being formed on the single monolithic chip. 
     
     
       3. The transmitter of  claim 2 , wherein the phase-lock-loop further includes a loop filter coupled between the phase detector and the oscillator, the loop filter being formed on the single monolithic chip. 
     
     
       4. The transmitter of  claim 3 , wherein the loop filter is a gm-c type filter. 
     
     
       5. The transmitter of  claim 3 , further including
 a track and hold circuit coupled between the loop filter and the oscillator, the track and hold circuit being formed on the single monolithic chip, the track and hold circuit holding the phase-lock-loop state prior to disabling the oscillator in the event of a ‘space’ transmission.  
 
     
     
       6. The transmitter of  claim 1 , wherein the phase-lock-loop further includes a prescaler and a divide-by-M circuit coupled between the oscillator and the phase detector, the divide-by-M circuit and the prescaler formed on the single monolithic chip. 
     
     
       7. The transmitter of  claim 1 , wherein the oscillator includes a voltage controlled oscillator. 
     
     
       8. The transmitter of  claim 1 , further including a reference oscillator formed on the single monolithic chip, the reference oscillator supplying a single reference frequency to the phase detector. 
     
     
       9. The transmitter of  claim 8 , wherein the reference oscillator is of the Colpitts variety and is coupled to receive a signal from a timing device external to the single monolithic chip. 
     
     
       10. The transmitter of  claim 1 , further including a charge pump formed on the single monolithic chip for operating the single monolithic chip at low input power voltage levels, the charge pump supplying a voltage to the oscillator. 
     
     
       11. The transmitter of  claim 1 , further including a bandgap reference circuit formed on the single monolithic chip, the bandgap reference circuit generating reference voltages that are temperature and supply voltage stable. 
     
     
       12. The transmitter of  claim 1 , further including a data encoder formed on the single monolithic chip, the data encoder coupled between a data input pad and the oscillator. 
     
     
       13. A transmitter comprising:
 an oscillator forming part of a phase-lock loop (PLL), the oscillator in combination with the phase-lock loop generating a transmit frequency of the transmitter in response to a frequency reference, the oscillator including a resonant network;  
 a modulator, a portion of said oscillator and said modulator being formed on a single monolithic chip, wherein part of the resonant network is formed on the monolithic chip, the resonant network of the oscillator being completed by an antenna formed external to the single monolithic chip, a resonance frequency of said resonant network being automatically tuned by the phase-look loop to the transmit frequency,  
 wherein the phase-lock-loop further includes a phase detector and a loop filter, the loop filter being coupled between the phase detector and the oscillator, the phase detector and the loop filter being formed on the single monolithic chip; and  
 a track and hold circuit coupled between the loop filter and the oscillator, the track and hold circuit being formed on the single monolithic chip, the track and hold circuit holding the phase-lock-loop state prior to disabling the oscillator in the event of a ‘space’ transmission.  
 
     
     
       14. The transmitter of  claim 13 , wherein the loop filter is a gm-c type filter. 
     
     
       15. The transmitter of  claim 13 , wherein the phase-lock-loop further includes a prescaler and a divide-by-M circuit coupled between the oscillator and the phase detector, the divide-by-M circuit and the prescaler formed on the single monolithic chip. 
     
     
       16. The transmitter of  claim 13 , wherein the oscillator includes a voltage controlled oscillator. 
     
     
       17. The transmitter of  claim 13 , wherein the oscillator includes a differential structure of varactor diodes for tuning a resonance point of the antenna to the frequency of the oscillator. 
     
     
       18. The transmitter of  claim 17 , further including
 a varactor charge pump formed on the single monolithic chip to provide a bias charge for varactor diodes in the differential structure of varactor diodes.  
 
     
     
       19. The transmitter of  claim 13 , further including a reference oscillator formed on the single monolithic chip, the reference oscillator supplying a single reference frequency to the phase detector. 
     
     
       20. The transmitter of  claim 19 , wherein the reference oscillator is of the Colpitts variety and is coupled to receive a signal from a timing device external to the single monolithic chip. 
     
     
       21. The transmitter of  claim 13 , further including a charge pump formed on the single monolithic chip for operating the single monolithic chip at low input power voltage levels, the charge pump supplying a voltage to the oscillator. 
     
     
       22. The transmitter of  claim 13 , further including a bandgap reference circuit formed on the single monolithic chip, the bandgap reference circuit generating reference voltages that are temperature and supply voltage stable. 
     
     
       23. The transmitter of  claim 13 , further including a data encoder formed on the single monolithic chip, the data encoder coupled between a data input pad and the oscillator. 
     
     
       24. A transmitter comprising:
   an oscillator forming part of a phase - lock loop  ( PLL ) , the oscillator generating a transmit frequency of the transmitter based on a reference frequency;        a modulator, a portion of the oscillator and the modulator being formed on a single monolithic chip;        a resonant network connected to the oscillator, the resonant network including an antenna external to the monolithic chip and a controllable variable capacitance formed on the monolithic chip, a resonance frequency of said resonant network being tuned to the transmit frequency; and        a controller for receiving a first signal generated internal to the monolithic chip, the first signal being related to a detected phase in a transmit signal, and, in response, controlling the variable capacitance to vary the capacitance of the variable capacitance so that the resonance frequency of the resonant network is the frequency of the oscillator.     
     
     
       25. The transmitter of  claim 24  wherein the phase- lock - loop further includes a phase detector, the phase detector being formed on the monolithic chip.   
     
     
       26. The transmitter of  claim 25  wherein the phase- lock - loop further includes a loop filter coupled between the phase detector and the oscillator, the loop filter being formed on the single monolithic chip.   
     
     
       27. The transmitter of  claim 26  wherein the loop filter is a gm- c type filter.   
     
     
       28. The transmitter of  claim 24  further comprising a phase detector, the first signal being based on an output of the phase detector. 
     
     
       29. The transmitter of  claim 28  wherein the controller controls the variable capacitance to achieve a certain output of the phase detector. 
     
     
       30. The transmitter of  claim 24  wherein the resonant network forms part of the oscillator. 
     
     
       31. The transmitter of  claim 24  wherein the resonant network forms part of the oscillator, and wherein a frequency of the oscillator is controlled, at least in part, by controlling the variable capacitance. 
     
     
       32. The transmitter of  claim 24  wherein the oscillator includes a voltage controlled oscillator. 
     
     
       33. The transmitter of  claim 24  further including a reference oscillator formed on the monolithic chip, the reference oscillator supplying a single reference frequency to the phase detector. 
     
     
       34. The transmitter of  claim 33  wherein the reference oscillator is coupled to receive a signal from a timing device external to the monolithic chip. 
     
     
       35. The transmitter of  claim 24  wherein the variable capacitance comprises a controllable p- n junction.   
     
     
       36. The transmitter of  claim 24  wherein the variable capacitance comprises at least one varactor diode. 
     
     
       37. The transmitter of  claim 24  further including a data encoder formed on the single monolithic chip, the data encoder coupled between a data input pad and the oscillator. 
     
     
       38. The transmitter of  claim 24  wherein the modulator is an AM modulator. 
     
     
       39. The transmitter of  claim 24  wherein the modulator is an FM modulator. 
     
     
       40. A method of operating a transmitter comprising:
   generating a transmit frequency of the transmitter by an oscillator forming part of a phase - lock loop  ( PLL ) , an oscillator frequency being based on a reference frequency, the oscillator being formed on a monolithic chip;        modulating the oscillator frequency;        the transmitter including a resonant network connected to the oscillator, the resonant network including an antenna external to the monolithic chip and a controllable variable capacitance formed on the monolithic chip, a resonance frequency of said resonant network being tuned to the transmit frequency; and        receiving, by a controller, a first signal generated internal to the monolithic chip, the first signal being related to a detected phase in a transmit signal, the controller controlling the variable capacitance to vary the capacitance of the variable capacitance so that the resonance frequency of the resonant network is the frequency of the oscillator.