Patent DE 10 2016 119 927

Standardised communication protocols between different electronic chips are a basic requirement for the design of modern electronic systems. Established protocols, which are supported by most commercial chips, are often associated with relatively high energy requirements during communication. A new circuit concept can reduce the energy requirement and thus extend the operating time of battery-operated systems or extend the applicability of the protocols to alternative supply concepts such as energy harvesting.

Signal transmission between electronic system components is often handled via a serial signal bus. Various communication protocols are used, such as SMBus, ^I2C, 1-wire or SPI. Many of these protocols require pull-up resistors that create a defined high level on the signal bus, which can be pulled to low level for signalling. The continuous current flow via the pull-up resistors contributes significantly to energy consumption when such signal buses are used in ultra-low-power and battery-operated systems (e.g. RFID sensor transponders).

The idea behind the invention is a novel circuit concept in which pull-up resistors are dispensed with and the charging energy for a level change is provided very energy-efficiently by a pull-up emulator. The pull-up emulator circuit 01, includes

• State memory (latch with input 02, output 03), which is connected to a charging line 04,
• Set switch S2, which in the closed state switches on a high level to the charging line 04 and the state memory connected to it by applying a supply voltage _Vsupply ; when open, it disconnects 04 from _Vsupply so that a high-impedance state prevails at node 05,
• Probe switch S1, which in the closed state switches the charging line 04 and the state memory connected to it to a bus node PU that can be connected to the signal bus,
• Control circuit Ctrl, clocked by an oscillator OSC.

Within a predetermined operating cycle, the control circuit sets the set switch

• the set switch S2 to the closed state in order to set the state memory to high level,
• the probe switch S1 to the closed state,
• after a predetermined overlap time, set switch S2 to the open state,
• the probe switch S1 to the open state.

The overlap time is dimensioned such that the charging energy provided during the closed state of switches S1 and S2 is sufficient to switch the bus capacity of the signal bus connected to bus node PU from the low level to the high level, provided that the signal bus is idle.

Advantages of the invention

• The charging energy for a level change on a signal bus is provided very energy-efficiently by the pull-up emulator.
• The circuit is generally suitable for different bus systems and any signal frequencies.
• No adaptations are required for conventional system components connected to the bus. The circuit can therefore be easily integrated into conventional bus systems.