如何使用Codeigniter连接sql server数据库？

Help will be appreciated.
I am stuck and I am facing an error of Invalid DB driver Error. I had done research from my end. I had installed the driver of sqlsvr and add the extensions in php.ini file. I believe the driver is okay with the PHP version.

extension=php_pdo_sqlsrv_71_ts.dll and extension=php_sqlsrv_71_ts.dll in php.ini file. Then I try to make a connection with Codeigniter Database.

$active_group = 'default'; $query_builder = TRUE;

$db['default'] = array(
    'dsn'   => '',
    'hostname' => 'DESKTOP-Q52QI3K',
    'username' => 'noman',
    'password' => 'noman',
    'database' => 'TestDB',
    'dbdriver' => 'sqlsvr',
    'dbprefix' => '',
    'pconnect' => TRUE,
    'db_debug' => TRUE,
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

I have this database on my local SQL server management tool. I am still facing the Invalid DB driver error.

After lot of research, I found an alternate solution. I would like to share it, in future may be it will help someone.

$serverName = "IP_Address";
$connectionInfo = array( "Database"=>"DBName", "UID"=>"Username", "PWD"=>"Password");
$conn = sqlsrv_connect( $serverName, $connectionInfo );
if( $conn === false ) {
    die( print_r( sqlsrv_errors(), true));
}else{
     echo "connected";
}

I use the custom php connection with sql database.