PHP - problema con conexion a base de datos postgre

pg_connect

Fatal error: Call to undefined function pg_connect() in C:\xampp\htdocs\tesis1\actualizacion.php on line 4

$user = "postgres";

$password = "000";

$dbname = "000";

$port = "5432";

$host = "localhost";

$cadenaconexion = "host=$host port=$port dbname=$dbname user=$user password=$password";

$cadenaconexion = "host=$host port=$port dbname=$dbname user=$user password=$password";

$conexion = pg_connect($conexion) or die("Error en la Conexión: ".pg_last_error());