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U. Glaeser

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FIGURE 17.7 DVS improvement for UI process.<br />

FIGURE 17.8 Voltage converter negative-feedback loop.<br />

measured frequency value, F MEAS. This value is subtracted from F DES to find the frequency error, F ERR.<br />

The loop filter implements a hybrid pulse-width/pulse-frequency modulation algorithm [9], which<br />

generates an M P or M N enable signal. The inductor, L DD, transfers charge to the capacitor, C DD, to generate<br />

a V DD, which is fed back to the ring oscillator to close the loop.<br />

The only external components required are a 4.7 µH inductor (L DD) placed next to the converter, 5.5 µF<br />

(C DD) of capacitance distributed near the chips’ V DD pins, and a 1 MHz reference clock. The ring oscillator<br />

is placed on the processor chip, and is designed to track the critical paths of the microprocessor over<br />

voltage. A beneficial side effect is that the ring oscillator will also track the critical paths over process and<br />

temperature variations. The rest of the loop is integrated onto the converter die.<br />

New Performance Metrics<br />

In addition to the supply ripple and conversion efficiency performance metrics of a standard voltage<br />

regulator, the DVS converter introduces two new performance metrics: transition time and transition<br />

energy. For a large voltage change (from VDD1 to VDD2), the transition time is:<br />

© 2002 by CRC Press LLC<br />

Crystal<br />

Oscillator<br />

V DD<br />

V DD<br />

f 1MHz<br />

RST<br />

Counter<br />

Max. Speed<br />

Idle<br />

Without Voltage Scheduler<br />

Increased Speed<br />

to Meet Deadlines<br />

Processor Clock<br />

f CLK<br />

F MEAS<br />

F DES<br />

Σ<br />

0101100<br />

Register<br />

t TRAN<br />

With Voltage Scheduler<br />

Ring Oscillator<br />

F ERR<br />

Loop Filter<br />

Low Speed & Idle<br />

P CTL<br />

N CTL<br />

I DD<br />

Processor<br />

FET Control<br />

& Drivers<br />

2CDD ≈<br />

------------ VDD2 – VDD1 IMAX V BAT<br />

M P<br />

M N<br />

LDD VDD C DD<br />

Power<br />

FETs Discretes<br />

Buck Converter<br />

(17.4)

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