interface my_interface1
 // Some signals
 modport tb_to_dut (
    // Signal directions specified
 )
endinterface

interface my_interface2
 // Some signals
 modport tb_to_dut (
    // Signal directions specified
 )
endinterface

interface my_combined_interface
  my_interface1 inf1
  my_interface2 inf2
endinterface

interface my_combined_interface
  my_interface1 inf1
  my_interface2 inf2

  modport tb_to_dut (
     inf1.tb_to_dut,
     inf2.tb_to_dut
  )
endinterface