Continued from Toshiba Halves Current Consumption of BLE SoC (1)

As for the signal reception architecture suited for low current consumption, in general, two times higher oscillating frequency is used to perform frequency conversion at one time. This method prevents the interference from mobile phone signals but consumes a large current.

In view of this, Toshiba employed a method that uses the same (1x) oscillating frequency and conducts frequency conversion two times. However, this method makes the frequency organization complicated and increases the susceptibility to interference.

This time, Toshiba solved the problem of the susceptibility by using an optimal frequency plan (a combination of the number of frequency divisions and the frequency of the VCO (voltage controlled oscillator) embedded in the PLL) that prevents the interference from mobile phone signals.

Frequency conversion is performed twice with the new method (right). (image courtesy of Toshiba)

In regard to the power supply system with a high conversion efficiency, a DC-DC converter and an LDO are generally combined. However, the power consumption of the LDO is large. Therefore, Toshiba employed a method that uses only a DC-DC converter without an LDO.

The elimination of an LDO increases the influence of the switching noise of the DC-DC converter. This time, Toshiba fixed the switching frequency of the DC-DC converter by using a PLL so that it is not within the desired frequency band of BLE.

As for the low-current-consumption RF circuit, one VCO is generally shared by the transmission and reception systems. This time, however, each of the transmission and reception systems has a VOC. As a result, the necessary frequency variable range was narrowed, lowering current consumption. Also, Toshiba applied a switching amplifier to circuits such as the circuit of a power amplifier, further lowering current consumption.

A VCO is used for each of the transmission and reception systems. (image courtesy of Toshiba)

With those low-current-consumption technologies, Toshiba realized a practical wireless performance (reception sensitivity: -93dBm, transmission output: 0dBm) and a 50% lower current consumption (3.2mA at the time of receiving signals and 3.5mA at the time of transmitting signals) at the same time.