Microchip Technology MCP6V01RD-TCPL Data Sheet
MCP6V01/2/3
DS22058C-page 22
© 2008 Microchip Technology Inc.
4.1.2
AUTO-ZEROING ACTION
shows the connections between amplifiers
during the Normal Mode of operation (
φ
1
). The hold
capacitor (C
H
) corrects the Null Amplifier’s input offset.
Since the Null Amplifier has very high gain, it
dominates the signal seen by the Main Amplifier. This
greatly reduces the impact of the Main Amplifier’s input
dominates the signal seen by the Main Amplifier. This
greatly reduces the impact of the Main Amplifier’s input
offset voltage on overall performance. Essentially, the
Null Amplifier and Main Amplifier behave as a regular
op amp with very high gain (A
Null Amplifier and Main Amplifier behave as a regular
op amp with very high gain (A
OL
) and very low offset
voltage (V
OS
).
FIGURE 4-2:
Normal Mode of Operation (
φ
1
); Equivalent Amplifier Diagram.
shows the connections between amplifiers
during the Auto-zeroing Mode of operation (
φ
2
). The
signal goes directly through the Main Amplifier, and the
flywheel capacitor (C
flywheel capacitor (C
FW
) maintains a constant correc-
tion on the Main Amplifier’s offset.
The Null Amplifier uses its own high open loop gain to
drive the voltage across C
The Null Amplifier uses its own high open loop gain to
drive the voltage across C
H
to the point where its input
offset voltage is almost zero. Because the principal
input is connected to V
input is connected to V
IN
+, the auto-zeroing action
corrects the offset at the current common mode input
voltage (V
voltage (V
CM
) and supply voltage (V
DD
). This makes
the DC CMRR and PSRR very high also.
Since these corrections happen every 100 µs, or so,
we also minimize slow errors, including offset drift with
temperature (
we also minimize slow errors, including offset drift with
temperature (
ΔV
OS
/
ΔT
A
), 1/f noise, and input offset
aging.
FIGURE 4-3:
Auto-zeroing Mode of Operation (
φ
2
); Equivalent Diagram.
4.1.3
INTERMODULATION DISTORTION
(IMD)
(IMD)
The MCP6V01/2/3 op amps will show intermodulation
distortion (IMD), products when an AC signal is
present.
The signal and clock can be decomposed into sine
wave tones (Fourier series components). These tones
interact with the auto-zeroing circuitry’s non-linear
distortion (IMD), products when an AC signal is
present.
The signal and clock can be decomposed into sine
wave tones (Fourier series components). These tones
interact with the auto-zeroing circuitry’s non-linear
response to produce IMD tones at sum and difference
frequencies. IMD distortion tones are generated about
all of the square wave clock’s harmonics.
Clock randomization spreads the IMD tones across the
frequency spectrum, but cannot eliminate them. The
spread energy is low and is not correlated with the sig-
nal of interest, so it is not of concern for most precision
applications. See
frequencies. IMD distortion tones are generated about
all of the square wave clock’s harmonics.
Clock randomization spreads the IMD tones across the
frequency spectrum, but cannot eliminate them. The
spread energy is low and is not correlated with the sig-
nal of interest, so it is not of concern for most precision
applications. See
.
V
IN
+
V
IN
–
Main
Output
V
OUT
V
REF
Amp.
Buffer
NC
Null
Amp.
C
H
C
FW
V
IN
+
V
IN
–
Main
Output
V
OUT
V
REF
Amp.
Buffer
NC
Null
Amp.
C
H
C
FW