Signal expander
AssigneeRCA Corporation
InventorsTodd J. Christopher, Gopi N. Mehrotra
Life of this patent
Estimating the term…
Abstract
The envelope of an input signal to be expanded is detected and applied via an adaptive filter to the gain control input of a variable gain device which expands the input signal. The adaptive filter provides improved ripple reduction and transient response characteristics and comprises a low pass filter for producing a smoothed control signal and an analog gate for coupling the greater of the smoothed control signal or a further signal to the variable gain device, the further signal being equal to the filter input signal less two predetermined constants. The gate further includes plural current paths selectively enabled for different conditions of the low pass filter input and output signals for augmenting the supply of current to the filter.
Claims6
A signal expander, comprising, in combination:
- input means for receiving an input signal to be expanded;
- detector means responsive to said input signal for producing a first control signal having an amplitude which varies as a function of the envelope of said input signal;
- variable gain means having a first input terminal coupled to receive said input signal, a second input terminal for receiving an expansion control signal and an output terminal for providing an expanded output signal;
- and
- adaptive filter means responsive to said first control signal for producing said expansion control signal and supplying said expansion control signal to said second input terminal of said variable gain means, said adaptive filter means comprising:
- low pass filter means including a capacitor and a current source means, said curent source means being responsive to said first control signal produced by said detector means for supplying charging current to said capacitor proportional to a potential difference, V.sub.1 -V.sub.2, wherein V.sub.1 is a voltage proportional to said first control signal and V.sub.2 is a voltage stored in said capacitor as a result of the charging thereof and independent of the instantaneous value of said charging current;
- and
- analog gating means for coupling the greater of said second voltage, V.sub.2, or a third voltage, V.sub.3, to said second input terminal of said gain control means, the voltage V.sub.3 being equal to a potential difference V.sub.1 -K.sub.1 -K.sub.2 wherein K.sub.1 and K.sub.2 are each non-zero constants, said analog gating means including a first current path for augmenting the current supplied to said capacitor when the voltage V.sub.1 exceeds V.sub.2 +K.sub.1, said analog gating means also including a second current path for augmenting the current supplied to said capacitor when the voltage V.sub.1 exceeds V.sub.2 +K.sub.1 +K.sub.2.
Dependencies are inferred from the claim text.