Signal processing circuit, AGC circuit, and recording and playback device
Disclosed herein is a signal processing circuit including: a main path configured to transmit an input signal and output an actual signal; and a negative feedback path configured to feed back the actual signal to an input stage of the main path, wherein the main path includes a main path block that receives an input signal and outputs an actual signal, the negative feedback path includes a negative feedback block that generates a control signal and supplies the control signal to an input part of an input signal of the main path; a replica block that is supplied with a control signal of the negative feedback block to output a pseudo actual signal, and imitates the main path block; and a signal delay block that delays a pseudo actual signal of the replica block by a dead time of a loop.
1. A signal processing circuit comprising:
a main path configured to transmit an input signal and output an actual signal; and
a negative feedback path configured to feed back the actual signal to an input circuit of the main path, wherein
the main path includes
a main path circuit that receives the input signal and outputs the actual signal,
the negative feedback path includes
a negative feedback circuit that generates a control signal and supplies the control signal to an input side of the main path;
a replica circuit that is supplied with the control signal of the negative feedback circuit to output a pseudo actual signal, and imitates the main path circuit; and
a signal delay circuit that delays the pseudo actual signal of the replica circuit by a dead time of a loop,
a first local negative feedback loop including a dead time is so formed as to include
the negative feedback circuit,
the replica circuit, and
the signal delay circuit,
a second local negative feedback loop including no dead time is formed by the negative feedback circuit and the replica circuit, and
the first local negative feedback loop synthesizes a synthesized signal from an output signal of the signal delay circuit and the actual signal and inputs the synthesized signal to the negative feedback circuit.
2. The signal processing circuit according to claim 1 , wherein
transfer characteristics of the replica circuit and the signal delay circuit are adjusted depending on a transfer characteristic of a circuit coupled thereto.
3. The signal processing circuit according to claim 2 , wherein
a relationship represented by Expression 1 is satisfied if a transfer function of the main path circuit is A(s), a transfer function of the replica circuit is A′(s), a transfer function of the signal delay circuit is N(s), and a transfer function of an actual signal delay circuit is M(s).
A
′
(
s
)
=
A
(
0
)
M
(
0
)
N
(
s
)
=
A
(
s
)
M
(
s
)
A
(
0
)
M
(
0
)
(
Expression
1
)
4. The signal processing circuit according to claim 1 , wherein the negative feedback path includes:
a synthesizer that synthesizes an output signal of the signal delay circuit and the actual signal and outputs a synthesized signal in the first local negative feedback loop; and
a subtractor that subtracts a pseudo actual signal of the replica circuit in the second local negative feedback loop from the synthesized signal and inputs a signal resulting from the subtraction to the negative feedback circuit.
5. An automatic gain control circuit comprising:
a main path configured to adjust amplitude of an input signal and output an actual signal; and
a negative feedback path configured to feed back amplitude information of the actual signal to an amplitude adjustment stage in the main path, wherein
the main path includes
a variable gain unit that varies amplitude of an input signal depending on a control signal,
the negative feedback path includes
an amplitude detector that detects amplitude of an actual signal output from the main path; and
a controller that generates the control signal from amplitude information by the amplitude detector and target amplitude and outputs the control signal to the variable gain unit,
the controller includes
a negative feedback circuit that generates a control signal and supplies the control signal to an input of the main path;
a replica circuit that is supplied with the control signal of the negative feedback circuit to output a pseudo amplitude signal, and imitates the main path; and
a signal delay circuit that delays a pseudo amplitude signal of the replica circuit by a dead time of a loop,
a first local negative feedback loop including a dead time is so formed as to include
the negative feedback circuit,
the replica circuit, and
the signal delay circuit,
a second local negative feedback loop including no dead time is formed by the negative feedback circuit and the replica block circuit, and
the first local negative feedback loop synthesizes a synthesized signal from an output signal of the signal delay circuit and an amplitude signal of an actual signal and inputs the synthesized signal to the negative feedback block.
6. The automatic gain control circuit according to claim 5 , wherein
transfer characteristics of the replica circuit and the signal delay circuit are adjusted depending on a transfer characteristic of a circuit coupled thereto.
7. The automatic gain control circuit according to claim 6 , wherein
a relationship represented by Expression 2 is satisfied if a transfer function of the main path is A(s), a transfer function of the replica circuit is A′(s), a transfer function of the signal delay circuit is N(s), and a transfer function of an actual signal delay circuit is M(s).
A
′
(
s
)
=
A
(
0
)
M
(
0
)
N
(
s
)
=
A
(
s
)
M
(
s
)
A
(
0
)
M
(
0
)
(
Expression
2
)
8. The automatic gain control circuit according to claim 5 , wherein
the controller includes:
a first subtractor that subtracts detected amplitude by the amplitude detector from the target amplitude;
a synthesizer that synthesizes an output signal of the signal delay circuit and an output signal of the first subtractor and outputs a synthesized signal in the first local negative feedback loop; and
a second subtractor that subtracts a pseudo actual signal of the replica circuit in the second local negative feedback loop from the synthesized signal and inputs a signal resulting from the subtraction to the negative feedback circuit.
9. The automatic gain control circuit according to claim 5 , wherein
the variable gain unit includes
a multiplier that multiplies an input signal and the control signal, and
the controller has a function to compensate nonlinearity of the multiplier.
10. A recording and playback device comprising:
a pickup element configured to pick up information of a recording medium; and
an automatic gain control circuit configured to adjust a signal level picked up by the pickup element, wherein
the automatic gain control circuit includes
a main path that adjusts amplitude of an input signal and outputs an actual signal; and
a negative feedback path that feeds back amplitude information of the actual signal to an amplitude adjustment stage in the main path,
the main path includes
a variable gain unit that varies amplitude of an input signal depending on a control signal,
the negative feedback path includes
an amplitude detector that detects amplitude of an actual signal output from the main path; and
a controller that generates the control signal from amplitude information by the amplitude detector and target amplitude and outputs the control signal to the variable gain unit,
the controller includes
a negative feedback circuit that generates a control signal and supplies the control signal to an input of the main path;
a replica circuit that is supplied with the control signal of the negative feedback circuit to output a pseudo amplitude signal, and imitates the main path; and
a signal delay circuit that delays a pseudo amplitude signal of the replica circuit by a dead time of a loop,
a first local negative feedback loop including a dead time is so formed as to include
the negative feedback circuit,
the replica circuit, and
the signal delay circuit,
a second local negative feedback loop including no dead time is formed by the negative feedback circuit and the replica circuit, and
the first local negative feedback loop synthesizes a synthesized signal from an output signal of the signal delay circuit and an amplitude signal of an actual signal and inputs the synthesized signal to the negative feedback block.