A typical LCD has the advantages of portability, low power consumption, and low radiation.  LCDs have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like.  Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions. 
A conventional LCD typically includes a liquid crystal panel, a backlight module illuminating the LCD panel, and a backlight modulation circuit modulating illumination of the backlight module. 
FIG.  5 shows a backlight modulation circuit 1 in an LCD, comprising a signal processing section 120, a signal modulation section 130, and a backlight modulation section 140. 
The signal processing section 120 includes an input terminal 121 configured to receive an external command.  The signal processing section 120 converts the external command to a backlight modulation signal, and outputs the backlight modulation signal to the signal modulation section 130.  After receiving the backlight modulation signal, the signal modulation section 130 modulates a backlight driving signal controlling the illumination of the backlight module, via a pulse width modulation (PWM) or pulse frequency modulation (PFM) method according to the backlight modulation signal.  A modulated backlight driving signal is output to the backlight modulation section 140.  Accordingly, the backlight modulation section 140 modulates the illumination of the backlight module, thereby achieving an appropriate illumination level for the LCD. 
The backlight modulation circuit 1, having only one signal processing channel, can only process one kind of backlight modulation signal at a time, typically a coarse modulation signal or a fine modulation signal.  Thus regulating of the illumination of the backlight module by the backlight modulation circuit 1 can only be achieved in one of a large, broad range or a small, precise range at any one time.  That is, if illumination of an LCD employing the backlight modulation circuit 1 is to be modulated in both a large range and a precise range, the backlight modulation circuit 1 must modulate the illumination twice via two separate modulation commands.  This is inefficient and time-consuming. 
It is thus desired to provide a new backlight modulation circuit and a backlight modulation method which can overcome the limitations described.