Tags » Power Amplifier

Evolution of a concept…

I’ve been playing with the (somewhat) unusual combination of a class A amp and a switching PSU before (here). The previous version worked quite well, but even as I was building it I though that there might be scope for optimisation and for making it smaller – which to be honest was my goal all along. 329 more words

Audio

Power Bryston 14B SST

http://www.hifiwigwam.com/showthread.php?124583-For-Sale-Bryston-14B-SST-Power-Amplifier-Pre-owned

http://www.audioemotion.co.uk/bryston-14b-sst-power-amplifier—pre-owned-8643-p.asp

Description: Solid-state, dual-mono power amplifier with balanced and unbalanced inputs. Specified output power (at 2kHz): 600Wpc into 8 ohms (27.8dBW), 900W into 4 ohms (26.5dBW). 87 more words

Power Amplifier

Project files: Amplifier PSUs

Digging in the back catalogue a bit again here.…and found some of my power supply boards that I haven’t published yet :)

What is it? 579 more words

Audio

How to Tune Load Optimization With Simulation

前一個Power Amplifier Design & Measurement章節有提到,所有的放大器都有最佳的負載阻抗,這個阻抗是有實虛部 (如R+j*X),這最佳負載阻抗是取輸出功率等高線(Output Power Contours)及功率放大器效率PAE(PA Efficiency),的取最佳平衡的性能的阻抗區的位置,通常是選在這兩大等高線的”重合區域”,其一般這兩個等高線不會完全疊合在一起,只有部分疊合在一起,所以必須有些取捨。

Ref[1] EXAMPLE: Swept_Load_Pull_Measurements_Complete by NI AWR

NOTE:怎麼取得最佳的負載阻抗,可以利用Load Pull System去量測到,請參考下列參考網址。
STEP Electronics Ltd.史泰佳科技股份有限公司
1.Hybrid Active Load Pull… 176 more words

RF

Power Amplifier Design & Measurement

早期的無線產品由於SoC, System on chip化有一些極限,所以通常會將功率放大器放在IC外部,新型的SoC都已經將功率放大器給包進IC內,不過還是有些Out-door的產品,會外掛功率放大器,這個章節說明一下,功率放大器如何調整及量測。

下面為RICHWAVE的IC,型號RTC6665,應用於2.4 GHz 802.11b/g,可以在OFDM(64QAM, 54Mbps)有18 dBm輸出,小訊號可放大26 dB,屬於小功率放大。(一般網通界稱的大功率放大器,小訊號放大要大於30dB)

NOTE:這裡提到的小訊號為S參數,大訊號為實際上調變訊號。

Ref[1] Product No:RTC6665 by RichWave

由應用電路可以看出,這顆放大器是MMIC形式,外部元件相當少,其每個外部元件的功用皆寫在圖片上

接下來看功率放大器內部電路,內部很簡單,主要是一個電晶體(transistor),及偏壓電路,可以看到這顆是採用AB類放大器,所以會犧牲一些負訊號,置於切掉多少負訊號,就要看偏壓電路如何設計,這需要一些性能及訊號完整的平衡設計。

接下來看一下這顆規格書,紅色框選的是小訊號可以量測驗證的參數,特別需要去量測1dB的增益飽和點,由於真實世界的功率放大器不可能輸入多少,而無限制的持續放大增益,一定會有輸入飽和的問題,1dB的增益飽和點就是去定義輸入訊號達多少,輸出會有飽和的現象。

什麼是1dB的增益飽和點,就是輸入能量從低打到高,輸出的功率因為飽和,而輸出功率降了1dB的那個點,所以這參數的圖X軸為輸入功率,Y軸是輸出功率。
1.量測他的放大功率輸出為 19.6dB
2.外部輸出衰減-10dB

測試方法為,持續增加輸入功率,看輸出功率少1dB,以這顆放來器來說,輸入達-1.8dBm時,輸出功率少了1dB,即找到1dB的增益飽和點。
所以P1dB=19.6+10dB-1.8dBm=27.8dBm… 106 more words

RF

An unusual clone…

Well, it isn’t actually that unusual when you look at it, but to most audiophiles these days cloning a Harman/Kardon amplifier doesn’t make a lot of sense – they’re nothing special. 336 more words

Audio

Project files: LM1875 Gainclone

What is it?
The project files for my mini gain clone with the LM1875 IC as described here. The download file includes both the amplifier board and the matching PSU-board. 400 more words

Audio