This presentation is a part of course on Analog CMOS design. It discusses the Bandwidth enhancing technique using RF amplifiers. Discussion is on shunt-peak amplifier, shunt-series peaking, shunt and double-series peaking.

1. Zeros as Bandwidth Enhancer

2. Contents
• Bandwidth
• Why to increase Bandwidth
• Techniques of bandwidth enhancing
1. Shunt Peaked Amplifier
2. Shunt Series Peaked Amplifier
3. Shunt & Double Series Peaked Amplifier

3. Bandwidth
• Its a measure of the width of a range of frequencies
• Bandwidth is the difference between the upper and lower
frequencies in a continuous set of frequencies.
• It is typically measured in Hertz

4. Why to Increase Bandwidth?
• The main reason for bandwidth enhancement is to increase the
Operating Region of the device.
• In MOS transistors, bandwidth can be extended by increasing the load
impedance.
• There are many techniques of enhancing the bandwidth like Series-
Shunt Peaking amplifiers, Frequency Doublers etc.
One of the way to achieve this is to add a zero in the transfer function
of output impedance of the amplifier by using circuitry like shunt-
series peaking.

5. • Gain of CS Amplifier α Load
Impedance
• As frequency increases; Impedance of
Capacitor decreases
• If an Inductance is connected in series
with Capacitive Load, then
Impedance of load increases with
increase in frequency
• Addition of an Inductance => Addition
of zero in the Load Impedance
Shunt Peaked Amplifier

6. Shunt Peaked Amplifier(contd..)
shunt peaked amplifier Model of shunt peaked amplifier

7. Output Impedance:
• The output impedance of RLC network is given by:

8. • As frequency increases:
1. The term in numerator increases, The magnitude Z(s) increases
• As frequency decreases
2. The term will also increase magnitude of Z(s)
• => As Z(s) increases, the Bandwidth increases.

9. Issue with the above approach: Choice of L
For a given value of R & C, there is no single optimum value of L that
we can choose.

10. Solution
• Choose a term arbitrary term ‘m’ given by:

11. • By choosing a value of ‘m ‘ that leads to desired behavior of the
circuit, we can possibly maximize the bandwidth
• Taking
We can extend Bandwidth to 1.85 times as larger than
uncompensated circuit.

12. Condition m = (R^2)C/L Normalized Bandwidth
Maximum Bandwidth 1.41 1.85
Maximum flat frequency response 2.41 1.72
No shunt peaking Infinite 1

13. Similar Techniques
• Shunt-Series Peaking
• Shunt and Double Series Shunt Peaking

14. Shunt-Series Peaking
Series shunt peaking
• Much better Bandwidth Extension
method
• The Bandwidth Boost is by complex
poles ; introduced in the Load
Transfer function.
• L1 is chosen as earlier
• L2 can be chosen as:

15. Shunt and Double Series Peaking
• Introduction of L3 delays the diversion
of current into rest of the network=>
the transistor drives only its output
capacitance for some time
• Rise time increases=>Bandwidth
increases
• Bandwidth & Delay trade-off
Double-Series shunt peaking

16. Thank You