| 摘要 |
<p>The switched capacitor voltage converter 102, which may be used to provide a high voltage to bias a MEMS microphone, causes dips in the reference voltage VBG in each cycle because charge is taken from this node to recharge the input capacitors CCP and CCPB. The control circuit 201 of the reference voltage generator acts to restore the reference voltage, but this action is accompanied by a transient in the voltage VPG at the gate of the transistor 202. The current IXA in the transistor 202 may be mirrored in transistor 301 to provide a bias current IXB to a source follower preamplifier (103, figure 3) for the MEMS microphone output signal. To prevent the transient in the node VPG causing a transient in the preamplifier bias current IXB, the switch 601 is opened for a short time interval whenever either of the capacitors CCP or CCPB is connected to the reference voltage VBG. The capacitor CC2 reduces the duration of the transient.</p> |
