| 摘要 |
<p>An amplification circuit has an amplifier with at least a first amplification device, and a switchable attenuation circuit with one or more switches and a plurality of attenuation devices operable to provide different levels of attenuation to a signal input to said amplifier depending on the status of the switches (fig.1). An embodiment comprises a switchable amplifier 300 and a switched attenuator 100. The attenuator 100 comprises a switched capacitive attenuation ladder SW1-SW2, CA1-CA2 and CB1-CB2. For medium to large inputs, switch 900 is closed and transistor 600b bypassed and gain is controlled by closing SW1 or SW2. For low signals, SW1 and SW2 are open and the input is isolated from transistor 600a. An un-interrupted switch-free path then connects the low level signal to transistor 600b which together with transistor 600a acts as a cascode amplifier. By providing a separate switch free path for small signals, the problem of (resistive) switch noise is overcome, while still providing selectable attenuation for larger input signals. A differential version of the circuit is disclosed (fig.5).</p> |
