In contemporary wireless handheld devices, the switching power supply is gradually replacing linear regulators to extend battery life. But it also makes noise source (Switching Power Supply), and noise-AC capacitor sensitive circuits exist in the product, which will lead to a disruption of the hidden danger. 



The traditional solution is to stay away from the noise source circuit noise sensitive circuitry. But for all the components are very tight integration of the modern handheld devices, this approach is no longer viable. Shielding methods used in the cost and size of the two, has been unworkable. Traditional switching power supply noise energy will be concentrated in a narrow band harmonics. However, if these harmonics in a sensitive happen with a frequency (for example, the receiver's IF-band) line, it may cause interference.

An existing programme

One has been successful on the technology used in DC / DC (DC / DC) converter system clock for the high-frequency jitter. The method and the method of the spread spectrum operation, allowed through a AC capacitor sequence of pseudo-random number (PRN) switching frequency modulation, to eliminate narrow-band harmonics. In essence, this is the noise will be "scattered" in the entire frequency range, but is no longer focusing on specific harmonics on. Spread-spectrum noise due to the peak amplitude of a lot of low, interference was significantly inhibited. Although the technology is discrete devices in the past success of the way, but with the progress of technology, spread spectrum technology can be integrated in the current update of the DC / DC converter, which can significantly save space. .

Spread spectrum operation with a single IC low noise programme

In order to understand how to achieve on-chip spread spectrum operation, we have to see Figure 1 shows the block diagram. Figure 1 in the duplex switched-capacitor charge pump for the input voltage buck with a stable output voltage. Regulators through an external resistor divider output voltage detection signal modulation and error under the charge pump output current way to achieve it. A two-phase non-overlapping clock for the excitation of these two charge pump. This charge pump two-phase parallel each other but to work. Clock in the first phase, from the current VIN switching through a pump, through an external floating capacitor to VOUT. Not only in the first phase will be sent to the current VOUT, this floating capacitor to recharge. Clock in the second phase, a variable capacitor from VOUT was grounded, will be the first phase of the clock through the stored charge pump switching transported to a VOUT. Pump AC capacitor 2 work in the same manner, but with the opposite charge pump phase 1. The duplex structure from a VIN to VOUT sustained charge transfer at the same time, can greatly reduce output and input noise.