How I can to open the calendar extender when click in the textbox

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VB

I used the the calendar extender ajax toolkit ...
I wanna when click in the textbox the calendar open
....
How i can do this

What I have tried:

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server" />
               <asp:TextBox ID="TextBitrh" runat="server" Width="120px"></asp:TextBox>
               <asp:ImageButton ID="ImageButton1" runat="server" Height="25px"
                   ImageUrl="~/images (2).jpg" Width="25px" />
               <asp:CalendarExtender ID="CalendarExtender1" runat="server" Format="dd/MM/yyyy"
                   PopupButtonID="ImageButton1" PopupPosition="BottomRight"
                   TargetControlID="TextBitrh">
               </asp:CalendarExtender>