<?php

class Conexion {

       function Conectar(){
            try{
                $servidor = "localhost";
                $user = "root";
                $pass = "";
                $db = "bdejemplos";
                $con = new PDO("mysql:host=$servidor;dbname=$db",$user,$pass);
                echo 'conectado';

            }  catch (Exception $e){
                echo 'Error '. $e->getMessage();
            }
           return $con;
    }
}

?>

***OpClientes.php***
<?php
include './Conexion.php';
//include_once '../entidades/Clientes.php';

class OpClientes {

    function NCodigo() {

        $con = new Conexion();
        $con->Conectar();
        //$cli = new Clientes();
        //$sql = "call bdejemplos.IdCliente(?)";
        $sql = "SELECT nom FROM `clientes where id = ?";
        $consulta = $con->prepare($sql);
        if ($consulta->execute(array('miguel'))) {
            while ($fila = $consulta->fetch()) {
                echo "$fila";
            }
        }
    }

}

$c = new OpClientes();
$c->NCodigo();

?>

Fatal error: Call to undefined method Conexion::prepare() in
 C:xampphtdocsejemplosModelosOpClientes.php on line 14