Nanosurf easyPLL User manual

1
UHV Preamplifier
Reference Manual
easyPLL

1
Table of Contents
easyPLL UHV-Pre-Amplifier for Tuning Fork 2
Theory ............................................................................................... 2
Wiring of the pre-amplifier ................................................................ 4
Technical specifications ................................................................... 5
Version 1.1
BT 00536

2
easyPLL UHV-Pre-Amplifier for Tuning Fork
Theory
For high resolution AFM measurements a sensor with high mechanical
stiffness (high spring constant) is of geat interest. A quartz tuning fork
with integrated tip not only offers this feature but simplifies things as
simple electronics can then be used to detect the oscillation. The quarz
tuning fork is built into an oscillation circuit as the resonance determin-
ing element and is operated at its resonance frequency. When scanning
across the sample the variations in the resonance frequency are used to
control the distance between tip and sample.
To integrate the quartz tuning fork into the electrical oscillator, two in-
terfacing elements are needed: a transducer, used to convert the electri-
cal excitation signal into mechanical oscillations and a converter, used to
convert the forks response into a electrical signal.
A piezo electrical actuator is used as a transducer for the excitation sig-
nal. It is must be attached as close as possible to the basis of the fork and
mechanically oscillates the quartz tuning fork at the excitation frequency.
The movement of the fork’s prongs is measured by electrodes situated on
the prongs and converted into an electrical signal using a highly sensi-
tive pre-amplifier.
In 1
Out
R
In 2 Piezo actuator
Carrier
Tuning
Fork
Sample
To minimize noise these two transducer elements have to be attached as
close as possible to the tuning fork. This means the pre-amplifier must
be constructed so that it is Ultra High Vacuum (UHV) compatible.

3
The rest of the excitation circuit can be set up outside the UHV and can
be set up in two different ways. On one hand as a self-oscillator with
subsequent frequency measurements and on the other hand as a PLL
tracking oscillator. Both methods can be ideally implemented using the
easyPLL FM Sensor Controller and the easyPLL Digital FM Detector.
Z-
Feedback
Scan Control
easyPLL Digital FM DetectoreasyPLL FM Sensor Controller
Oscillator Detector
Phase
shift
X
Amplitude
control
RMS
DC
+
-
Piezo
actuator
Set point
Quartz Tuning Fork
f
in
Error
signal
PC
Parallel
port
Low Pass
Low Pass
on/off
Voltage
Controlled
Digital
Oscillator
(VCDO)
+
+
XFrequency
deviation
fref
PI-Control
f
ref
Control
Lock Range
Polarity
Gain
Offset
Output
UHV Pre-Amplifier
self oscillator
Z-
Feedback
Scan Control
easyPLL Digital FM DetectoreasyPLL FM Sensor Controller
Oscillator Detector
X
Amplitude
control
RMS
DC
+
-
Piezo
actuator
Set point
Quartz Tuning Fork
f
in
Error
signal
PC
Parallel
port
Low Pass
Low Pass
on/off
Voltage
Controlled
Digital
Oscillator
(VCDO)
+
+
XFrequency
deviation
fref
PI-Control
f
ref
Control
Lock Range
Polarity
Gain
Offset
Output
UHV Pre-Amplifier
Phase
shift
PLL tracking oscillator

4
Wiring of the pre-amplifier
This section describes version 3.01 of the UHV preamplifier.
The pre-amplifier should be mounted in the UHV chamber as close to
the quartz tuning fork as possible.
Use of 2 × 100 W resistors for Vs buffering and 10 kWresistor for tip
bias buffering recommended (should be placed outside the vacuum cham-
ber).
When mounting ensure that only UHV compatible materials are used!
CAUTION: ESD sensitive device! Ensure that you are well grounded
when mounting the per-amplifier so as to avoid electrostatic discharge
which could destroy the pre-amplifier!
7 signals have to be fed into the UHV chamber:
- +15V power supply
- -15V power supply
- reference ground of the amplifier
- signal out of the amplifier
- tip bias
- piezo electrode 1
- piezo electrode 2
2 signals are connected to the electrodes of the quartz tuning fork:
- current input A of the amplifier
- current input B of the amplifier

5
-Vs
+Vs
GND
tip
bias
Vout
Pre Amplifier
A
B
158
tip contacted to
terminal A though
tuning fork electrode
10k
100
100
V 3.01
Technical specifications
Power supply:
Voltage: ± 15V ±10%
Quiescent current: < ± 3mA
Sensitivity: ~1mV/Å
Noise: 150 fm/Hz½
(when used with E158 qPlus sensor)
Max. tip bias: ±10 V
Storage temperature: - 65°C to +150°C
Operation temperature: - 40°C to +85°C
Feedback Resistor: 30 MOhm

6
P arameter M in T yp M ax U ni ts
INPUT OFFSET VOLTAGE
1
Initial Offset 0.3 2 / 1 / 1 mV
T
MIN
to T
MAX
3/2/ 2 mV
vs. Temp 7 20/20/
20 µV/°C
vs. Supply
76 95 dB
T
MIN
to T
MAX
76/76/ 76 dB
Long-Term Stability 15 µV/Month
INPUT BIAS CURRENT
2
V
CM
= 0 V 15 50 pA
V
CM
= 0 V @ T
MAX
1.1/3.2/51 nA
V
CM
= ±10 V 20 100 pA
INPUT OFFSET CURRENT
V
CM
= 0 V 10 25 pA
V
CM
= 0 V @ T
MAX
0.6/1.6/26 nA
FREQUENCY RESPONSE
Small Signal Bandwidth 3.0 4.0 MHz
Full Power Response 200 kHz
Slew Rate
16 20 V/µs
Settling Time to 0.01% 1.0 1.2 µs
Total Harmonic Distortion 0.0003 %
INPUT IMPEDANCE
Differential 3 ×10
12
5.5 ΩpF
Common Mode 3 ×10
12
5.5 ΩpF
INPUT VOLTAGE RANGE
Differential
3
±20 V
Common-Mode Voltage
4
+14.5, -11.5
T
MIN
to T
MAX
-V
S
+ 4 +V
S
- 2 V
Common-Mode
Rejection Ratio
V
CM
= ±10 V 76 88 dB
T
MIN
to T
MAX
76/76/ 76 84 dB
V
CM
= ±11 V 70 84 dB
T
MIN
to T
MAX
70/70/ 70 80 dB
INPUT VOLTAGE NOISE 2 µV p-p
45 nV/√Hz
22 nV/√Hz
18 nV/√Hz
16 nV/√Hz
INPUT CURRENT NOISE 0.01 pA/√Hz
OPEN-LOOP GAIN
150 400 V/mV
100/100/
100 V/mV
OUTPUT CHARACTERISTICS
Voltage
+13,- 12.5 +13.9, -13.3 V
±12/±12/±
12 +13.8, -13.1 V
Current 25 mA
POWER SUPPLY
Rated Performance ±15 V
Operating Range ±
4.5 ± 18 V
Quiescent Current 2.5
3. 4 mA
NOTES
1
Input Offset Voltage specifications are guaranteed after 5 minutes of operation at T
A
= +25°C.
2
Bias Current specifications are guaranteed maximum at either input after 5 minutes of operation at
A
= +25°C. For higher temperatures, the current doubles every 10°C.
3
Defined as voltage between inputs, such that neither exceeds ±10 V from ground.
4
Typically exceeding -14.1 V negative common-mode voltage on either input results in an output phase reversal.
Specifications subject to change without notice.
T

Nanosurf AG
Grammetstrasse 14
CH-4410 Liestal
E-Mail
inf[email protected]
World Wide Web
www.nanosurf.com
Nanosurf AG, 2002
Version 1.1 BT0053
Printed in Switzerland
©