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DC NANOVOLT AMPLIFIER MODEL A10
The EM A10 is a low level amplifier module for sensitive measurements, data collection and systems, where
signals below 1 nanovolt may be measured. It is ideal for the input unit for precision voltage measuring
systems, requiring voltage sensitivity for measuring low noise and low impedance sources. The noise level
of the A10 is equivalent to a perfect resistor of 20 ohms. When used with a digital voltmeter, steady one
nanovolt digits may be displayed, with a response time constant of less than a second. The input voltage
stability of the A10 is very high, with the drift around a nanovolt per degree C. The input connectors are
made from pure copper. The input impedance is very high, and is time dependent, determined by the
internal loop gain of the amplifier. The very high DC gain of greater than five million million means that high
overall gain may be used, controlled precisely by feedback resistors, thus ensuring a good degree of
linearity with the accuracy defined by the feedback resistors used. Despite the gain, the A10 is stable with
100% feedback. This allows a filter capacitor to be used across the feedback resistor to control the rise time
and noise from the measurement circuit. The loop gain is reduced from the DC figure of five million million
at the rate of 30 dB per frequency decade to unity at 20 KHz. This determines the response time of the
amplifier, which will vary according to the set gain. The A10 can deliver 2 milli-amps of current from its output
and so the set gain will determine the level of output signal at low values of gain less than 1,500. The internal
'low' feedback resistor is 1 ohm, and so if a gain of unity is set by connecting the output to the feedback
terminal directly, the maximum output voltage will be 2 millivolts. The internal feedback resistor needs to be
this low, because the noise generated by this resistor is in series with the input noise, and any higher
resistance would cause a significant increase in the total A10 noise. The power consumption is very low,
making the A10 suitable for battery powered applications. The minimum supply voltage is plus and minus
5.5 volts and the quiescent current consumption is 1.5 milli-amps. Care is required over the choice of power
supply, if batteries are not to be used, to ensure that the very low noise of the A10 is not degraded by series
mode or common mode noise being allowed to interfere with small signals. The A10 has very high rejection
of common mode noise, but at nanovolt levels great care must be taken. The A10 is small enough to mount
on a p.c. board if required, and the case is made of heavy gauge Mumetal to give an extra degree of
magnetic and electrostatic screening. The voltage and current offset controls are accessible with a small
insulated trimming tool through the two holes in the front. Care must be taken with these adjustments.
DC NANOVOLT AMPLIFIER MODEL A10
Noise Output Level
Equivalent noise resistance is typically 20 ohms. The A10 will provide an output up to +/- 3V D.C.
Noise voltage depends on bandwidth, e.g. rise at 2mA load, including the current taken by the
time constant 1 second gives a peak to peak feedback resistor.
noise voltage of 1 nanovolt. There is no 1/f com-
ponent. Connectors
The input connectors are 3mm studs and nuts in
Offset Voltage pure copper. All other connectors are M3 brass
Adjustable to zero. T.C. 1nV per deg C slow studs and nuts.
change or 5nV per deg C differential.
Power Supply
Offset Current Minimum +/- 5.5V at 1.5mA quiescent. Maximum
Adjustable to zero. T.C. typically 5pA per deg C +/- 12V. Nominal supply +/- 6V
Gain and Bandwidth Dimensions and Weight
Greater than 5e13 at DC reducing to unity at Length 120mm. Width 70mm. Height 35mm. +
20KHz. Amplifier gain is set using an external 6mm for terminals. Weight 490gm.
feedback resistor.
The fixed internal feedback component is 1 ohm Fixing
+/- 1% 5 ppm, so for a gain of 10,000, the feed- 4 Holes required 3mm diameter. 114mm X 54mm.
back element must be 9999 ohms.
Input Resistance Note: Feedback Components
Greater than 1 Gohm, with gain set to 1 million or There is an internal feedback resistor from the
less, subject to time following an input step func- 'Feedback' terminal to the input 'Lo' of 1 ohm +/-
tion. 1% 5 ppm/degree C. The gain is set by connect-
ing an external resistor from 'Output' to
Source Resistance 'Feedback' . The value of this resistor is Rfb =
The A10 closely follows the source Johnson noise (gain required - 1) ohms. i.e. Gain = 10,000, Rfb
characteristic from source resistance of 20 ohms = 9999 ohms. As the internal feedback resistor
up to about 5K ohms. With source resistances has a tolerance of 1%, the external feedback
below 20 ohms the noise is substantially constant resistor needs to be adjusted by +/- 1%. The gain
down to zero ohms. stability will be 5ppm per degree C plus the stabil-
ity of the applied feedback resistor.
Input Level
The A10 will operate with input voltages up to +/- There is a 10pF capacitor connected from
2mV. 'Output' to 'Feedback'
This Data Sheet is dated 2/11/2006 and is subject to change without prior notification