LONDON, England (CNN) -- The debate about using technology to help referees has been re-ignited following a number of controversial decisions in the Champions League semi-final between Chelsea and Barcelona.



The Hawk-Eye system is already widely used in tennis and has transformed the game.



Sepp Blatter, president of FIFA, the game's governing body, has consistently opposed the use of in-game video replays, but goal-line technology, to determine if the ball has crossed the goal line, has received more support.



The Hawk-Eye system is extensively used in tennis, using cameras to calculate the trajectory of the ball.



The system then uses the trajectory data to determine exactly where the ball has hit the ground, making it invaluable for marginal line calls.



Using similar technology, Hawk-Eye Innovations, based in England, has developed a football system to determine if a goal has been scored.



It again uses cameras to track the ball and computers to calculate its position. If the system detects that the ball has crossed the goal line a central computer transmits a signal to the referee via either a watch or earpiece.



The system was tested at Premier League football club Fulham in 2006 and then at Reading's training ground in 2007. It was backed by the British Football Association and funded by the Premier League.



Another goal-line technology, a microchipped football, was developed by Adidas and German firm Cairos Technologies. A microchip built into the football detects a magnetic field generated by underground cables in the penalty area. Like the Hawk-Eye system it uses a computer to send a signal to the referee's watch when a goal is scored.



The system was tested at the World Under-17 Championships in 2005 and the 2007 World Club Championship in Tokyo.



The International Football Association Board (IFAB), which decides the laws of the game, discusses new rules at an annual general meeting consisting of four representatives from FIFA and one each from England, Northern Ireland, Scotland and Wales.



Explaining the IFAB's decision, Blatter said the microchipped ball had failed in one of the seven World Club Championship matches because of interference to the signal sent to the referee and that it would be difficult to implement the chip technology in the many types of football used around the world.



He added that it was not possible to ensure that the Hawk-Eye system worked in a crowded goalmouth, where players might block the cameras' view of the ball.



"FIFA are of the opinion that the systems are very costly, would not add anything to the game and would harm the position of the referee," the UK's Press Association reported at the time.



Do you think goal-line technology should be used? Share your thoughts in the Sound Off box below.



But Hawk-Eye managing director Paul Hawkins told CNN that he believes FIFA has decided that it doesn't want technology in football.



"I saw FIFA last week and told them that we can provide a system if they want it, but it's very clear they don't want the system," he said.



Hawkins said his company cannot develop the technology any further without more testing in real stadiums, but that kind of testing requires FIFA's consent.



The idea that football's governing bodies are opposed to more technology in football has been supported by statements from the sport's governing bodies.



In March 2009, Blatter said in a statement: "The IFAB believes that football is a game for human beings and, as such, we should improve the standard of refereeing - and not turn to technology."



Michel Platini, President of UEFA, European Football's governing body, has expressed similar views.



Instead of pursuing goal-line technology, the IFAB chose to trial the idea of having two extra match officials, one behind each goal.



A FIFA spokesman told CNN that while the use of goal-line technology hasn't been ruled out forever, even after recent refereeing controversies, the IFAB's current position is to continue to experiment with extra officials.



The IFAB
What is FIFA opposed to? What is the name of the system that microchipped footballs? What is debate over? Who is opposed to video replays but has considered goal-line technology?
the use of in-game video replays, The Hawk-Eye about using technology to help referees Sepp Blatter, president of FIFA,
question: What is FIFA opposed to?, answer: the use of in-game video replays, | question: What is the name of the system that microchipped footballs?, answer: The Hawk-Eye | question: What is debate over?, answer: about using technology to help referees | question: Who is opposed to video replays but has considered goal-line technology?, answer: Sepp Blatter, president of FIFA,