Methods and devices are provided for circuits. One device includes an adjustment circuit having an adjustable resistor for modifying a resistance value of a resistive device, the adjustment circuit connected to an adjustment terminal of the resistive device. The resistance value of the adjustable resistor changes, when a voltage or charge on the adjustment terminal of the adjustable resistor is changed. The adjustable resistor is a phase change element with an adjusting terminal to which different voltage values are applied for adjusting a conversion device threshold value.