PCM coder and decoder circuit having digital balancing network
AssigneesHitachi, Ltd., Hitachi Micro Computer Eng. Ltd.
InventorsKazuo Yamakido, Takahiko Kozaki, Shigeo Nishita, Kenichi Ohwada
Life of this patent
Estimating the term…
Abstract
A PCM coder and decoder circuit for use in a subscriber line interface circuit of a telephone communication system has a digital balancing network for removing any echo signal. The digital balancing network is formed by series-connecting a first balancing circuit having characteristics corresponding to the fixed characteristics of a coder, decoder, etc. and a second balancing circuit having characteristics corresponding to variable characteristics of an external circuit including two-wire transmission line which is connected to the coder and decoder circuit. Thus, a replica of an echo signal is precisely produced, and the circuit configuration is simplified.
Claims3
In a PCM coder and decoder circuit having a D/A converter adapted to convert an input PCM signal into an analogue signal, and A/D converter adapted to convert an input analogue signal into a PCM signal, and a digital balancing network provided between the input terminal of said D/A converter and the output terminal of said A/D converter,
- the improvement which comprises:
- said digital balancing network being formed by cascade-connecting first and second balancing circuits, said first balancing circuit having predetermined non-variable characteristics approximated to transfer characteristics viewed from said digital balancing network toward said D/A converter and said A/D converter when the output terminal of said D/A converter and the input terminal of said A/D converter are shorted, and said second balancing circuit having characteristics approximated to the characteristics of a signal which is produced when a circuit having an impedance component is connected between the output terminal of said D/A converter and the input terminal of said A/D converter by a portion of the output of said D/A converter which undesirably enters said A/D converter through said circuit having an impedance component.
Dependencies are inferred from the claim text.