Datasheet

© 2011 Microchip Technology Inc. DS25007B-page 21
MCP6V26/7/8
4.0 APPLICATIONS
The MCP6V26/7/8 family of auto-zeroed op amps are
manufactured using Microchip’s state-of-the-art CMOS
process. This family is designed for low cost, low power
and high precision applications. Its low supply voltage,
low quiescent current and wide bandwidth make the
MCP6V26/7/8 devices ideal for battery-powered appli-
cations.
4.1 Overview of Auto-Zeroing
Operation
Figure 4-1 shows a simplified diagram of the
MCP6V26/7/8 auto-zeroed op amps. This will be used
to explain how the DC voltage errors are reduced in this
architecture.
FIGURE 4-1: Simplified Auto-Zeroed Op Amp Functional Diagram.
4.1.1 BUILDING BLOCKS
The Null Amplifier and Main Amplifier are designed for
high gain and accuracy using a differential topology.
They have a main input pair (+ and - pins at their top
left) used for the signal. They have an auxiliary input
pair (+ and - pins at their bottom left) used for correcting
the offset voltages. Both input pairs are added together
internally. The capacitors at the auxiliary inputs (C
FW
and C
H
) hold the corrected values during normal
operation.
The Output Buffer is designed to drive external loads at
the V
OUT
pin. It also produces a single-ended output
voltage (V
REF
is an internal reference voltage).
All of these switches are make-before-break in order to
minimize glitch-induced errors. They are driven by two
clock phases (φ
1
and φ
2
) that select between normal
mode and auto-zeroing mode.
The clock is derived from an internal R-C oscillator
running at a rate of f
OSC1
= 850 kHz. The oscillator’s
output is divided down to the desired rate.
The internal POR ensures the part starts up in a known
good state. It also provides protection against power
supply brown-out events.
The Digital Control circuitry takes care of all of the
housekeeping details of the switching operation. It also
takes care of POR events.
V
IN
+
V
IN
–
Main
Output
V
OUT
V
REF
Amp.
Buffer
NC
Null
Amp.
Null
Input φ
1
Switches
Null
Correct
φ
2
Switches
Null
Output
Switches
C
H
C
FW
POR
Digital
Control
Oscillator
φ
1
φ
2